FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

FERTILISATION GUIDELINES FOR THE TABLE GRAPE I NDUSTRY

KOBUS CONRAD I E • P I ETER RAATH DAWI D SAAYMAN • BENN I E D I EDER I CKS • KOBUS LOUW

FERTILISATION GUIDELINES FOR THE TABLE GRAPE I NDUSTRY KOBUS CONRAD I E • P I ETER RAATH DAWI D SAAYMAN • BENN I E D I EDER I CKS • KOBUS LOUW

FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY South African Table Grape Industry (SATI) 1st Floor 63 Main Road Suider-Paarl

Paarl 7464 www.satgi.co.za

© All rights reserved. No part of this book may be reproduced in any way, mechanical or electronic, including laser or tape recordings and photocopying, without the written permission of the publisher, except for reasonable citations for research and review purposes. Disclaimer: While reasonable care has been taken to ensure the accuracy of the information in this book, the author and publisher accept no responsibility for any consequences that may result from any error and / or omission. COMPILED FOR THE SOUTH AFRICAN TABLE GRAPE INDUSTRY By P.J.E. Louw April 2020

First edition 2020 978-0-620-89489-0 (e-book) Set in Berthhold Akzidenz Grotesk 9pt/11.5 DESIGN AND LAYOUT by Avant-Garde South Africa, www.theavant.co.za PRINTING by Shumani Mills Communications, Tygerberg

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KOBUS CONRADIE kobusconradie3@gmail.com

PIETER RAATH pjraath@sun.ac.za

DAWID SAAYMAN Dawid.saayman77@gmail.com

BENNIE DIEDERICKS bennie@resalt.co.za

KOBUS LOUW kobus@sapex.co.za

FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY | 3

RESEARCH & DEVELOPMENT FRAMEWORK

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VISION South Africa is the preferred country of origin for table grapes and will provide every table grape producer with as wide a choice as possible of profitable markets.

MISSION SATI delivers service excellence to create a progressive, equitable and sustainable South African table grape industry.

TOOLS Market Access & Development Information, Systems & Communication Transformation & Training Research & Technical

VALUES Science-based Agility and Flexibility Transparency Outcome-driven

DRIVERS Market Access:

“Market Preparedness” “Market Accessibility”

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VRGRAPHICS.CO.ZA_6691_0218633165

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CREATING A PROGRESSIVE, EQUITABLE AND SUSTAINABLE TABLE GRAPE INDUSTRY

63 Main Street | Paarl 7646 Western Cape | South Africa

Tel: +27 21 863 0366 | Fax: + 27 21 863 0339 Email: info@satgi.co.za | Website: www.satgi.co.za

Crop protection, like any other industry, needs smart people. Companies tuned in to their workforce understand that people want to succeed and be good at what they do. Education is just as valued as practical experience to achieve the professional success and status which employees strive to achieve. Villa is committed to provide a new generation of skilled people in agriculture and for our industry to be equipped with the latest knowledge, scientific facts and experience in the field of crop protection. The company therefore contributed funding for the establishment of a Chair in Crop Health at Stellenbosch University. This venture endeavours to focus on research driven by the needs of the agricultural industry, the education and financial support of students and the provision of further skills training for employees in the agronomic sector. The Chair in Crop Health is a first for South African agriculture. This is a major collaborative effort, and will see the integration of industry needs, industry partners and industry grower bodies with the work that our researchers and postgraduate students do. VILLA EDUCATES ON CROP PROTECTION BEST PRACTICES

The education leg of this endeavour strives not only to augment formal qualifications, but also to ensure continuous training options for agriculturalists and others already working in the local industry. The envisaged accredited short courses to be presented through the Chair in Crop Health will build on short courses, certificate and diploma courses previously developed by the Villa Academy. Lecturers from Stellenbosch University will be supported by others previously contracted by Villa Academy, as well as international colleagues from leading universities overseas. The curriculum will be characterised by strong emphasis on the problem-based method of learning in which students collaborate in groups to solve real-world examples of problems.

The crop chemicals business is rapidly evolving, and it has become highly technical. Villa is passionate about educating the people we work with in our industry to ensure that we have well equipped, well trained people in the agricultural business. We also actively participate and endorse publications of books such as this one to grow the knowledge of our industry even further. We’ve been through a decade of experiential and self-training, which just isn’t good enough for the environment we operate in. Knowledge is key! The local crop protection industry is worth around R9 billion rand at wholesale level and Villa is one of the leading suppliers of crop protection solutions to distributors in South Africa. The foundations of Villa

were already laid in 1989. It has since grown into a formidable force in crop protection solutions in South Africa. In its first commercial venture in Africa, the Fortune 250 global agribusiness and food company Land O’Lakes in 2015 acquired majority ownership of Villa Crop Protection. Land O’ Lakes, with its headquarters in America.

CONTENTS

1 INTRODUCTION ( Kobus Louw) _ _______________________________________________ 10 2 COLLECTION OF SOIL AND LEAF SAMPLES ( Pieter Raath) ______________________ 13 • SOIL SAMPLING __________________________________________________________ 13 – Sampling for soil preparation _________________________________________________ 13 – Sampling in existing vineyards _ _______________________________________________ 14 – Stony soil _ ____________________________________________________________ 14 – Handling of the samples _ ___________________________________________________ 15 • LEAF SAMPLING __________________________________________________________ 15 – Time of sampling _________________________________________________________ 15 – Leaf blade or petiole _ _____________________________________________________ 15 – Sampling protocol _ _______________________________________________________ 16 3 INTERPRETATION OF SOIL ANALYSIS REPORTS FOR VINEYARDS ( Pieter Raath) _ _ 19 • INTRODUCTION _ _________________________________________________________ 19 • TEXTURE _ ______________________________________________________________ 19 • SOIL ACIDITY OR ALKALINITY (pH) ___________________________________________ 20 • PLANT-AVAILABLE NUTRIENTS _______________________________________________ 20 • RESISTANCE _____________________________________________________________ 21 • PHOSPHORUS _ __________________________________________________________ 21 • POTASSIUM _ ____________________________________________________________ 23 • CALCIUM EN MAGNESIUM _ ________________________________________________ 24 • MICRO-ELEMENTS (BORON, MANGANESE, ZINC, COPPER) ________________________ 25 • BASIC CATION SATURATION RATIO (BCSR) AND SUFFICIENCY LEVEL OF AVAILABLE NUTRIENTS (SLAN) – COMPARISON OF THE CONCEPTS ___________________ 27 4 CHEMICAL CORRECTION OF SOILS DURING SOIL PREPARATION ( Dawid Saayman & Pieter Raath) _ ________________________________________________ 29 • NEGATIVE SOIL PROPERTIES ________________________________________________ 29 • CORRECTION OF SOIL ACIDITY ______________________________________________ 30 • LIMING MATERIALS _______________________________________________________ 32 • APPLICATION OF LIME _____________________________________________________ 33 • GYPSUM APPLICATIONS _ __________________________________________________ 33 • CORRECTION OF PHOSPHATE CONTENT _ ______________________________________ 34 • SUMMARY _ _____________________________________________________________ 35 5 MAINTENANCE FERTILISATION ( Pieter Raath, Kobus Conradie & Dawid Saayman ) _ ________37 • INTRODUCTION _ _________________________________________________________ 37 • NUTRIENTS REQUIRED BY GRAPEVINES _______________________________________ 38 – Quantities that are absorbed annually ____________________________________________ 38 – Distribution of elements between different organs ____________________________________ 38 – Seasonal uptake patterns ____________________________________________________ 39 • MACRO-ELEMENTS _ ______________________________________________________ 40 – Nitrogen (N) ____________________________________________________________ 40 – FERTILISATION PROGRAMME FOR NITROGEN ____________________________________ 43 – Fertilisation scheduling __________________________________________________ 43

8 | CONTENTS

CONTENTS

– Fertilisation according to production _ ________________________________________ 44 – Fertilisation according to soil analyses ________________________________________ 46 – Fertilisation according to vigour ____________________________________________ 47 – Fertilisation according to leaf analyses _ ______________________________________ 49 – Phosphorus (P) __________________________________________________________ 49 – Potassium (K) ___________________________________________________________ 52 – Calcium (Ca) _ __________________________________________________________ 58 – Magnesium (Mg) _ ________________________________________________________ 60 – Sulphur (S) _ ___________________________________________________________ 63 • MICRO- OR TRACE-ELEMENTS _ _____________________________________________ 65 – Iron (Fe) _ _____________________________________________________________ 65 – Manganese (Mn) _ ________________________________________________________ 67 – Zinc (Zn) ______________________________________________________________ 70 – Copper (Cu) ____________________________________________________________ 72 – Boron (B) ______________________________________________________________ 74 – Molybdenum (Mo) _ _______________________________________________________ 77 – Chlorine (Cl) _ __________________________________________________________ 77 • SUMMARY _ _____________________________________________________________ 79 6 PRACTICAL GUIDELINES FOR IMPLEMENTATION OF A FERTILISATION PROGRAMME ( Bennie Diedericks) ___________________________________________________________ 81 • INTRODUCTION _ _________________________________________________________ 81 • IMPLEMENTATION OF FERTILISATION PROGRAMME _ ____________________________ 82 • FERTILISATION PRODUCTS _ ________________________________________________ 85 • IMPACT OF FERTILISERS ON SOIL _ __________________________________________ 87 – Soil acidification _ _______________________________________________________ 87 – Increase in salt load ______________________________________________________ 88 – Soil biology ____________________________________________________________ 88 • ORGANIC FERTILISERS _ ___________________________________________________ 89 • MICRO-FINE LIME AND GYPSUM _ ___________________________________________ 90 • ROCK PHOSPHATE _ _______________________________________________________ 91 • MULCHES AND COVER CROPS _______________________________________________ 91 • FOLIAR NUTRITION _ ______________________________________________________ 92 • SUMMARY _ _____________________________________________________________ 93 7 THE RELATIONSHIP BETWEEN FERTILISATION, THE NUTRITIONAL STATUS OF A VINEYARD AND GRAPE QUALITY ( Pieter Raath & Kobus Conradie) _ ____________ 95 • NITROGEN _ _____________________________________________________________ 96 • PHOSPHOROUS _ _________________________________________________________ 98 • POTASSIUM _ ____________________________________________________________ 98 • CALCIUM _ ______________________________________________________________ 99 • MAGNESIUM ___________________________________________________________ 101 • SUMMARY _ ____________________________________________________________ 103 8 FERTILISATION OF ROOTSTOCK MOTHER BLOCKS AND NURSERIES ( Dawid Saayman) ____________________________________________________________ 105 • ROOTSTOCK MOTHER BLOCKS ______________________________________________ 105 • NURSERIES _ ___________________________________________________________ 106 9 REFERENCES ___________________________________________________________ 109

FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY | 9

1 INTRODUCTION

KOBUS LOUW

A manual providing guidelines for grape- vine fertilisation was published in 1994 (Conradie, 1994). This manual provided a solid basis for industry over the years, but after 20 years new local and international information has become available and must be made shared. So, the need to review the existing guidelines and to update it by incorporating new research results or per- spectives came about. In 2016, Winetech released a new set of fertiliser guidelines with a special wine focus. These guidelines are very similar to what was published by Conradie (1994) but incorporated substantial new information and was supported by the experience of a unique pool of expertise from South Africa. There was also a need to adapt and renew the guidelines for the table grape industry. The South African Table Grape Industry (SATI) approached the group of experts who were involved in the development of the guidelines for the wine industry, and requested that they adapt they guidelines into a new manual with a specific focus on table grape production, with its unique requirements. They were also requested to include new research results.

10 | INTRODUCTION

INTRODUCTION

South Africa is blessed with soil scientists and viticulturalists who have worked in the industry for a long time, each with a strong scientific background. Pieter Raath, Kobus Conradie, Dawid Saayman and Bennie Diedericks collaborated on the new set of guidelines. Scientific principles, which have been established over several years, as well as practical experience are unique- ly compiled in this manual to empower any advisor or table grape farmer.

The South African table grape industry faces many challenges. There are new producing countries, like Peru, who di- rectly compete with us in the market, and for this reason, the quality of our product is non-negotiable. This manual makes it possible for the table grape farmer to manage the fertiliser programme in a scientific, yet practical way to produce premium quality grapes that can be of- fered to the market with Pride.

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12 | COLLECTION OF SOIL AND LEAF SAMPLES

CHAPTER 2

2 COLLECTION OF SOIL AND LEAF SAMPLES SO I L SAMPLI NG The purpose of soil sampling and soil analysis is: • to predict the probability of a profitable reaction to application of fertiliser; • to evaluate and improve soil fertility; • to recommend practices for fertiliser and lime applications, and • to detect and correct imbalances in nutrient concentrations. Soil analysis is essential before soil preparation, to ensure that physical and chemical defects can be corrected during preparation. Regular analysis is required in existing vineyards to ensure that optimal conditions for growth are maintained. The most important benefit of soil analysis in existing vineyards is that changes in soil fertility can be observed and corrective measures may be applied, before nutritional problems that may harm grapevine performance, can develop. Sampling for soil preparation Profile pits are necessary to evaluate the physical/morphological characteristics and to determine the borders of management units. For smaller commercial areas, sampling should be done on at least a 50 m x 50 m grid. If the initial soil examination reveals that large soil differences occur between points, more pits should be dug to determine where the soil transitions are. Before commencement of sampling, the site should be divided into its various cultivation units. These units are areas which will be managed similarly because of soil form, soil depth and the incidence of coarse fragments. Separate samples are collected from each of these cultivation/management units and samples from the different sampling points within the same unit may be mixed in order to obtain representative samples for that management unit. The depth/thickness of the different horizons/layers, as well as an estimation of the coarse fraction must P I ETER RAATH

FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY | 13

also be noted. For soil preparation of vineyards, it is desirable to collect samples from the topsoil and subsoil separately. It is also often desirable to sample underlying clay material separately, since salts can move upwards to the overlying soil layers during dry periods. Sample labels must include the depth of sampling. A sample of 1 kg is enough. Sampling in existing vineyards The first samples ought to be taken shortly after soil preparation to establish whether optimal soil conditions have been created. Samples must be taken per management unit. To ensure that samples are representative of the management unit, they must constitute sub-samples taken from different places from within the unit. In instances where soil has been ridged, samples should only be taken from the ridge.  For maintenance fertilisation, soil samples must be taken at least every three years. However, in very sandy or stony soils, where extensive leaching of nutrients occurs, samples must be taken every two years. These samples are taken in the vine row. Because soil composition can vary drastically over short distances, long-term soil trends are best determined when samples are collected at more or less the same place each time. This is achieved by marking vines where samples are taken. Areas of the vineyard that are growing poorly should be sampled separately. Cultivation actions will often disturb the transition between soil layers, samples should therefore always be collected at the same fixed depths, in order to compile a historical record. These results can then be correlated with fertiliser applications. If the person who is responsible for the recommendations does not have records of previous analyses, more than one soil layer should be sampled. Because lime and phosphate fertilisers do not react immediately, samples should preferably be collected at depths of 0 – 150 mm and 150 – 450/500 mm. Taking into account that few roots are found at deeper soil levels, it is not necessary to sample more deeply. If the soil is shallower than 450 – 500 mm, sampling should be limited to above the restricting layer, because the presence of underlying clay in the sample, may lead to meaningless results. Stony Soil If the soil is very stony and the stones are so large that they cannot be sampled, an estimate of the incidence of stones must be made, i.e. indicate the volume occupied by stones. This information can have a significant effect on the fertiliser recommendation and must accompany the soil samples to the laboratory. A stone correction is used in the estimation of gypsum, lime, potassium and phosphate fertiliser requirements.

14 | COLLECTION OF SOIL AND LEAF SAMPLES

CHAPTER 2

Handling of the samples The composite sample is placed in a clean plastic bag and the bag is labelled with a name and the sample identity. If several composite samples were taken, each one must be labelled differently, and a record must be kept of the areas where each individual sample was taken. Only one form needs to be completed for each group of samples. The more complete the information provided, the better the recommen- dations will be. LEAF SAMPLI NG Leaf analysis can serve as a diagnostic tool for table grapes, but in practice it has the shortcoming that it is often affected by factors such as scion and rootstock combination, cultivation practices, cultivation area, seasonal climate, diseases and soil type. A general norm that makes provision for all conditions is, therefore, inevitably has a very wide range. Consequently, leaf analysis cannot be used as the only norm for establishing a fertilisation programme but should be supplementary to soil analysis. Leaf analysis can also be useful in case studies where leaves are sampled from “sick” vines, in addition to being sampled from adjacent, unaffected vines. The leaves from the healthy/better vines then serve as direct control, so that the time of sampling and all other variables are less critical or not applicable. No norm is used, but rather the relative differences between the two samples. The purpose of leaf analysis can therefore be summarised as follows: • It assists in evaluating the capacity of a soil to supply nutritional elements, and consequently serves as an aid to determine fertiliser calculations; • It indicates the effectiveness of fertiliser treatments on the nutritional status of grapevines; and • In instances where nutritional deficiencies are suspected, diagnosis can be done correctly. Time of sampling Leaf samples should be collected annually at the same physiological growth stage. In this regard fruit set or veraison can be used. Fruit set is understood to be the period extending from the end of flowering up to the pea berry stage (berries with a diameter of approximately 5 mm). At the time of veraison older leaves are often very dilapidated, but for certain elements like potassium (K), veraison remains a good time to sample. Leaf blade or petiole For vineyards in which the nutritional status varies, the petiole normally indicates larger differences than the leaf blade. The composition of the petiole also differs to a greater extent within the same vineyard compared to the leaf blade. Furthermore, the boron status is reflected better by the leaf blade than by the petiole. It is thus recommended

FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY | 15

that the petiole is sampled for analysis, but in certain cases it will be necessary to analyse the leaf blade as well. Norms for the elemental contents of leaf blades and petioles are indicated in Chapter 5. Sampling protocol The way in which vines are sampled for analysis has a major effect on the results obtained. As shown in Figure 1, leaves opposite the bunch are sampled at fruit set, or if this has been removed, the leaf between the third and the fifth node on a bearing shoot must be sampled. At veraison leaves must be sampled between the fifth and the eighth node from the growing point. Thirty leaf blades or petioles, immediately separated at sampling, are sufficient. Either one can be analysed although, as already discussed, petiole analyses are generally regarded as more accurate. The phenological stage (e.g. fruit set or veraison) of sampling must be indicated. Leaves should not be sampled during the hottest part of the day, since it can affect leaf composition. It is preferable to collect samples in the morning. Samples must be placed in a clean plastic or paper bag and should be kept cool until delivered to the laboratory. The samples must not be frozen under any circumstances.

Sampling at fruit set

Sampling at veraison

FIGURE 1: Positions where leaves should be sampled for analysis. SKETCHES FROM DAVENPORT & HORNECK (2011).

16 | COLLECTION OF SOIL AND LEAF SAMPLES

CHAPTER 2

If leaf analyses show that nutritional levels are beyond the norms (see Chapter 5), the fertilisation programme should be adjusted. However, leaf analyses must always be evaluated together with soil analyses and the physical appearance of the vineyard. A poorly growing vineyard with high nutrient levels may have experienced a critical water deficiency during an important growth stage.

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18 | INTERPRETATION OF SOIL ANALYSIS REPORTS FOR VINEYARDS

CHAPTER 3

3 INTERPRETATION OF SOIL ANALYSIS REPORTS FOR VINEYARDS

P I ETER RAATH & KOBUS CONRAD I E

I NTRODUCTI ON Soil sampling for analysis is regularly done by viticulturists and producers. Interpretation of the chemical results is often complicated on account of the variety of extraction methods and ways in which results are expressed (Van Schoor et al ., 2000). In this chapter the well-recognized analytical methods and the ways in which analytical results are expressed, as well as the interpretation thereof, are discussed. Other typical analytical methods are also discussed and compared with the accepted South African norms. The analytical methods that will be discussed, are by no means fully comprehensive, but are the ones that are the most studied and best understood in South African for cultivation of grapevines. In South Africa, soil analysis reports typically contain the following information and analytical results: TEXTURE Soil texture dictates the water holding capacity of a soil and the extent to which cations are bound to the soil’s negatively charged clay particles. The rate at which nutrients are leached from the root zone is therefore largely dictated by soil texture. Furthermore, potassium (K) and phosphorus (P) norms are affected by soil texture, making it essential to differentiate between sandy, loamy and clayey soils.

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The “finger method” can be used to assist in classifying the soil’s texture as either sandy, loamy or clayey. Alternatively, texture can be determined in the laboratory. Unfortunately, not all laboratories routinely report soil texture. Most laboratories will only report texture upon request. A full textural analysis can be carried out, to specify the exact percentages of sand, silt and clay. SO I L AC I D ITY OR ALKALI N ITY The pH of soil is determined in either potassium chloride (KCl) or water. Most laboratories in South Africa use the KCl method (pH KCl ), while most European and American laboratories determine a pH in water and report it as such (pH water ). Even though the difference between the two methods is not constant, soil pH KCl is roughly one pH unit lower than pH water . The reason for this is that the K + ions in the solution displace the H + on the clay lattices (the exchangeable H + ), which is then measured together with the active H + ions in the soil solution. A solution with a pH KCl below 5.5 (pH water < 6.5) is regarded as suboptimal for grapevines. The lower the pH, the more acidic the soil, e.g. there is a higher concentration of active hydrogen ions (H + ). The more acidic the soil, the higher the solubility of aluminium (Al 3+ ); until it reaches a toxic concentration that negatively affects root growth. Grapevines under perform in acidic soils due to poor root functioning, leading to reduced water and nutrient uptake as well as the possibility of pathogen and nematode infection. The optimal soil pH (pH KCl ) for grapevines varies between 5.5 and 6.5. For soils with lower pH values, lime should be applied to correct the situation. Various methods for determining the lime requirement have been developed. The Eksteen method has proven to be reliable for South African soil conditions and for vineyards (Eksteen, 1969). Calculation of the lime requirement is fully discussed in Chapter 4. Apart from root growth being increasingly impeded in acid soils, both P and molybdenum (Mo) become gradually less available for uptake. Acid soils are often also highly leached and depleted of nutrients like nitrogen (N), potassium (K), calcium (Ca) and magnesium (Mg). Where pH levels are higher than the above-mentioned optimal pH range, both P and the other micro-nutrients (except Mo) become less available for plant uptake. This is attributed to immobilisation when P reacts with Ca, and micro-nutrients with hydroxides and carbonates. To prevent nutrient deficiencies in soils with high pH values, regular P fertilisation and annual foliar applications of micro-nutrients is required. PLANT-AVAI LABLE NUTR I ENTS In South Africa plant-available nutrients are normally extracted by means one of two extraction agents – mostly ammonium acetate (NH 4 Ac), but some laboratories also use Mehlich III. Although laboratories will often refer to “exchangeable” nutrients in their reports, their figures normally indicate “plant-available” or “extractable” nutrients, which include “soluble” as well as “exchangeable” nutrients. In practical terms this means that the nutrients that could be leached out with water (soluble), are determined together

20 | INTERPRETATION OF SOIL ANALYSIS REPORTS FOR VINEYARDS

CHAPTER 3

with those that are retained on the clay lattice (exchangeable). As indicated later, it is especially important to keep the above-mentioned in mind for saline soils. RES I STANCE A saturated paste extract of the soil is prepared using distilled water, and its resistance (ability to allow an electrical current to flow through it) is measured. The unit in which resistance is expressed is “ohm” and is reciprocal to electrical conductivity (mS m –1 ). Salts, e.g. potassium, sodium and chloride, conduct electricity and therefore reduce the resistance of the soil solution. The lower the resistance measurement, the larger the quantity of salt in the soil, i.e. the soil is more saline. A resistance below 300 ohm indicates that excessive quantities of salts are present in the soil. At this level vine performance is negatively affected. The lower the resistance, the larger the negative impact on the vine will be. If the resistance is 200 ohm and less, the soil is classified as saline. Different salt fractions are encountered in soils. Both the soluble sodium percentage and the exchangeable sodium percentage (ESP), i.e. the percentage that Na constitutes as a fraction of the total amount of exchangeable cations (S-value), and the specific resistance serve as criteria for classifying the type of soil salinity. If the resistance of a saturated soil extract drops below 300 ohms (or conductivity of a saturated soil extract exceeds 400 mS m –1 ), with the ESP lower than 15%, the soil is classified as saline. Soil with an ESP > 15%, while containing free gypsum or lime, is classified as a “saline-sodic soil”. In both cases the salts may simply be washed out, using good quality irrigation water – provided that free gypsum is present, otherwise the soil colloids will disperse, making the soil impermeable for water. Where gypsum is not present in soils with ESP > 15%, the water that will be used for leaching should be saturated with gypsum before it comes into contact with the soil, or the gypsum requirement must be determined, for application of gypsum to the soil. PHOSPHORUS In soil analysis reports, phosphorus (P) is usually indicated in mg kg –1 . The optimal plant- available concentration depends on soil texture and soil pH. It is therefore important that laboratories also report the soil texture. Depending on the extraction method that was used, the norms for optimal P concentration will differ, because the extraction agents differ in pH and aggressiveness with which the P is extracted. A comparable list of norms is supplied in Table 1, indicating the applicable values for the most commonly used extraction agents. Because the amount of P extracted with Bray I, Bray II and Mehlich III, reduces as the soil pH increases, distinction needs to be made between the norms used for soils with different pH values. Furthermore, the P that is required to raise the concentration to the minimum required level might not necessarily be reflected when the soil is extracted at high pH. For soil with a pH regime that is regarded as optimal for grapevine production (e.g. pH KCl 5.5 to 6.0), Bray II and Mehlich III extraction provides similar values and most accurately reflects the available concentration of P in the soil.

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Bray I extractions are consistently lower and for vineyard soils the accuracy thereof, regarding P availability, has not yet been confirmed.

TABLE 1: Minimum soil phosphorus concentrations required for grapevines grown in different soil pH regimes, as applicable for different extractants # .

Extractant Olsen Citric acid Mehlich III

Soil pH KCl

Soil texture class

Bray I

Bray II

mg kg –1

Sandy Loamy Clayey Sandy Loamy Clayey Sandy Loamy Clayey Sandy Loamy Clayey

– – –

25 30 35 25 30 35 25 30 35 25 30 35

25 30 35 20 25 30 20 25 30 18 21 25

20 25 30 15 20 25 10 12 15 10 12 15

20 25 30 20 25 30 20 25 30 15 18 21

< 5.0

12 14 16 10 12 15 10 12 15

5.0 – 6.0

6.0 – 7.0

> 7.0

Sandy (0 – 6% clay) / Loamy (6 – 15% clay) / Clayey (>15% clay) # Data on the relative extractability of P with different extractants was supplied by C.P. Beyers, Nitrophoska. Olsen: 0.5M NaHCO 3 Citric acid: 0.05M citric acid (C 6 H 8 O 7 ) Mehlich III: 0.2M acetic acid (CH 3 COOH) + 0.25M NH 4 NO 3 + 0.015M NH 4 F + 0.13M HNO 3 + 0.001M EDTA

Bray I: 0.025M HCl + 0.3M NH 4 F Bray II: 0.1M HCl + 0.3M NH 4 F

22 | INTERPRETATION OF SOIL ANALYSIS REPORTS FOR VINEYARDS

CHAPTER 3

A simplified approach is mostly followed by laboratories serving the table grape industry, namely when the soil pH KCl < 7.0, either a citric acid, Bray I, Bray II or Mehlich III extraction is conducted and above-mentioned norms are used (Table 1). For soil with a pH KCl ≥ 7.0, an Olsen extraction is often done, and the norms in Table 1 are still used. The logic is that an Olsen extraction is less aggressive and is done at a higher pH, theoretically reflecting the lower rate of P release in the root zone better at higher soil pH conditions. For the Olsen extraction technique, however, it has been shown that only 5 – 7% of citric acid extractable P is extracted. This means that the total P in the soil can become excessively high (e.g. if extracted with Bray I or Bray II), while the Olsen P remains below the norm. It is therefore suggested that Bray I extractions are to be done on soils with pH KCl > 7.0, and the Bray I norms in Table 1 are used to calculate P requirements. If analysis is done with one of the other extractants, the provided norms can be used with reasonable reliability – but the use of Olsen extractions should preferably be avoided. Depending on the clay content of the soil, the P content should be augmented to the specific norm, as indicated in Table 1. For soil preparation the average P content is determined to a soil depth of 600 mm. To increase the P content by 1 mg kg –1 for 300 mm depth, 4.5 kg P should be applied, therefore 9 kg P per ha for 600 mm depth. On soils with high pH values (pH KCl > 7) it may be an option to adjust the recommended figure downwards and to increase the annual maintenance fertilisation volumes. For production vineyards the P content is calculated to a soil depth of 300 mm only, e.g. 4.5 kg P per ha must be applied for every 1 mg kg –1 with which the concentration must be increased. In the case of soils with high pH values, where P is easily fixed, the calculated, annual fertiliser requirement must be split over three installments and applied throughout the season. During harvest 0.7 kg P is removed for each ton of grapes produced and maintenance fertilisation should be calculated accordingly, except where soil analyses indicate that the P content is optimal or above the norm. It is important to avoid excessive applications of P, since this may restrict potassium uptake (Conradie and Saayman, 1989). Phosphate contents of more than 50 mg kg –1 in sandy soils, 60 mg kg –1 in loamy soils and 70 mg kg –1 in clayey soils, can be problematic at all pH values. The stone and gravel volume should therefore always be used in the calculation of the P requirement, to prevent over fertilisation with P. POTASS I UM As far as the grapevine’s potassium (K) nutrition is concerned, soil texture also plays an important role in the interpretation of soil analyses. Firstly, K is leached very quickly out of sandy soil, and secondly, clay minerals can play an important role in K fixing. Potassium applications are not recommended on sandy soils during soil preparation – leaching can easily occur on such soils. A broad norm that may be used for K nutrition on sandy soils, is an annual maintenance application of 3 kg K per ton of grapes produced.

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As already stated, in South Africa plant-available K is generally extracted by means of ammonium acetate (NH 4 Ac), but some laboratories also use Mehlich III. Similar results are obtained for the two extraction agents, with Mehlich III values being approximately 0.9 x NH 4 Ac (Sawyer & Mallarino, 1999; Nathan et al ., 2005). On heavier soils (loamy & clayey soils), the general norms, as indicated in Table 2, may be used as guidelines for maximum K values (Conradie 1994). These norms are linked to the differences in clay mineralogical types occurring in the various regions. In some cases, it can be K contents which constitute 4% of the total exchangeable cations, but preferential use of the 4% norm, as sometimes suggested, is discouraged.

TABLE 2: Maximum and excessive norms for potassium concentration in soil, as determined using ammonium acetate, to ensure optimal grapevine performance without affecting wine quality (Conradie, 1994).

Region

Coastal Breede River Olifants River Karoo Orange River

Maximum norm

70

80

100

100

120

mg kg –1

Excessive concentration

105

120

150

150

180

Adjustment of K levels during soil preparation is only required for heavier soils, where deficiencies are expected. The mean K concentrations is then determined to a soil depth of 600 mm, and for values below the above-mentioned norms, K fertilisation should be applied. In the case of producing vineyards, the K content is determined to a soil depth of 300 mm only. The requirement per hectare is 4.5 kg of K to increase the K content in the soil by 1 mg kg –1 over 300 mm depth. During soil preparation (to a soil depth of 600 mm), 9 kg K per ha should therefore be applied for each 1 mg kg –1 increase required. Since excessive K contents in the soil may cause problems with the uptake of magnesium (Mg) and storage ability, over fertilisation should be avoided. CALC I UM AND MAGNES I UM Both calcium (Ca) and magnesium (Mg) are essential nutrients, required for optimal grapevine performance. Generally, these nutrients are abundant in soils with pH values within the optimal range, making fertilisation of these nutrients unnecessary. Through properly calculated lime requirements and the right choice of lime type, sufficient Ca and Mg to satisfy the nutritional requirements of the grapevine, is applied to the soil (Eksteen, 1969). Nevertheless, some sandy soils with excessive volumes of stone might be deficient in Ca and Mg, even though the soil pH is optimal. Likewise, when the wrong type of lime (e.g. calcitic lime) is used for a Mg deficient soil, applications of Mg might be required.

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CHAPTER 3

Plant-available Ca and Mg can also be extracted by means of NH 4 Ac or Mehlich III. Similar results are obtained for the two extractants for soil with pH KCl < 6.0 (Nathan et al ., 2005). The following general norms may be used as guidelines for minimum Ca and Mg concentrations. The Ca:Mg ratio should preferably not exceed a value of 6.

TABLE 3: Minimum norms for calcium and magnesium concentration in soil, as determined using ammonium acetate, to ensure optimal grapevine performance.

Sandy soil

Clayey soil

Nutrient

mg kg –1

cmol (+) kg –1

mg kg –1

cmol (+) kg –1

Calcium

360

1.80 0.30

500 120

2.50 1.00

Magnesium

40

MI CRO-E LEMENTS (BORON, MANGANESE, ZI NC, COPPER) Soil analysis reports for vineyards usually indicate zinc (Zn), manganese (Mn), boron (B) and copper (Cu) contents as mg kg –1 . Zinc, Mn and Cu are extracted with EDTA, HCl or DTPA, while B is extracted with hot water. As soil pH increases the extraction efficiency of HCl reduces dramatically, making it unsuitable for use on soils with a pH KCl > 5.0. Even at a pH of 5 and lower it does not extract Mn adequately (Table 4). Extraction levels with DTPA appear to be similar to that of EDTA.

TABLE 4: Comparison of EDTA and HCl as extractants for micro-nutrients in soils of different pH values (Lambrechts, unpublished).

Cu (mg kg –1 )

Zn (mg kg –1 )

Mn (mg kg –1 )

Soil pH KCl

EDTA

HCl

EDTA

HCl

EDTA

HCl

5.0 6.0

0.36 0.28 0.21

0.45 0.17 0.07

0.64 0.51 0.41

0.80 0.23 0.07

67

17

34

5

7.0

17

1.4

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The grapevine requires small quantities of micro-nutrients and the availability thereof is directly dependent on the pH of the soil solution. Where the pH is high, manganese (Mn) and zinc (Zn) are inaccessible to the plant since these elements do not remain in the solution. Sometimes these elements may therefore be present in the soil, without being accessible to the plant. Consequently, soil analysis is not always a reliable means of determining the availability of micro-elements. To ascertain whether the metals are excessive or insufficient, leaf analyses should be done. For soils with low pH, boron (B) and (Zn) deficiencies may be expected. On the other hand, Mn can be so soluble in low pH soils that it may become toxic to the vine. Lime applications will solve these problems, by making B and Zn more available to the plant and Mn less soluble (Van Schoor, 2001). In Table 5 the norms for optimal micro-nutrient concentrations in soil are provided. In cases where the concentrations of the nutrients in the soil are below these norms, deficiencies may occur. In such cases the vineyard should be monitored visually for deficiency symptoms. If there is still any doubt, leaf analyses should be done. In the past, Cu deficiencies very rarely occurred in vineyards, due to the use of fungicides that contained Cu. With the decline in use of these products, attention should also be given to this micro-nutrient.

TABLE 5: Minimum micro-nutrient concentrations in soils with pH KCl values of 5.0 to 6.5 (mg kg –1 ). B Mn Zn Cu 0.3 2.0 0.5 0.5

If deficiencies of micro-nutrients do occur, foliar application of nutrients is a simple solution. Table 6 may be used as a guideline to determine if the micro-nutrient status is optimal.

TABLE 6: Micro-nutrient concentrations in petioles, sampled at fruit set and veraison, for assessment of the nutritional status of vineyards. (mg kg –1 ).

Fruit set

Veraison

High to excessive tot excess

High to excessive tot excess

Deficient Sufficient

Deficient Sufficient

Micro-

nutrient

Fe *NB 30 – 180

*NA

< 25 30 – 200

*NB *NB *NB

Cu < 3 5 – 10

25 – 50

< 2.5 3 – 20

Zn < 15 20 – 150 Mn < 20 30 – 60 B < 25 30 – 70 Mo *NB 0.2-0.4

*NA

< 15 20 – 150 < 20 30 – 200 < 25 30 – 90 *NA 0.2 – 0.5

>300 >100

> 1500

> 150

*NA

*NA

*NA – not available.

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BAS I C CATI ON SATURATI ON RATI O (BCSR) AND SUFFI C I ENCY LEVE L OF AVAI LABLE NUTR I ENTS (SLAN) – COMPAR I SON OF THE CONCEPTS As a guideline according to which soil analyses are interpreted, and fertilisers are applied, the basic cation saturation ratio (BCSR) concept (better known as the Albrecht system), is sometimes used. It assumes that plants will only grow optimally if there is a balanced ratio of cations (Ca 2+ , Mg 2+ and K + ) for every soil, according to its cation exchange capacity (CEC). Fertilisation is therefore done according to the soil’s needs, and not the need of the plant. In a review article, Kopittke & Menzies (2007) traced the BCSR concept back to the late 1800s and found that since the origin thereof, research data has been incapable of proving the existence of any “ideal” basic cation saturation ratio. Instead, they found that promotion of the BCSR concept resulted in inefficient use of resources and fertilisers. Research by various scientists has shown that the SLAN (sufficiency level of available nutrients) concept, where a minimum concentration of available nutrients in the soil is required for optimal plant nutrition, also applies to vines. Even though the “ideal” soil for grapevines can vary dramatically from region to region and between different soil types, its composition is based on a minimum level of nutrients that is required in the soil to supply the vine with the nutrients it requires. Nutrient element balancing is used in some cases to evaluate soil. This technique uses, for example, a Ca:Mg ratio of approximately 6 to indicate whether calcitic or dolomitic lime should be used. For vineyard soils the ideal saturation percentage of exchangeable cations is: Ca 80%, Mg 15% and K 4%, leading to a Ca:Mg:K ratio of about 20:3.75:1. In practice, however, it is not necessary to aspire to this “ideal” ratio for grapevines. Producers are therefore motivated rather to follow the SLAN concept, by making use of the minimum norms as provided in this manual. This will prevent over fertilisation and is an easier, scientifically more justifiable approach, applicable for all soil types.

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28 | CHEMICAL CORRECTION OF SOILS DURING SOIL PREPARATION

CHAPTER 4

4 CHEMICAL CORRECTION OF SOILS DURING SOIL PREPARATION

DAWI D SAAYMAN & P I ETER RAATH

NEGATIVE SO I L PROPERTI ES Soils upon which table grapes are generally cultivated in South Africa, are divergent as far as physical and chemical properties are concerned. In the coastal region (Paarl vicinity) the parent material consists of very old and highly weathered shale and granite, resulting in soils with a poor nutritional status, and a low exchangeable capacity, while acidity increases with soil depth. Even though these soils are generally well-drained, they are nevertheless compact. Together with the soil acidity this is restrictive to root development in the deeper layers. Vineyards next to the Berg River and in the Saron areas are generally situated on younger alluvial material, while acidity may also be relevant. In the inland areas, stony, alluvial soils, as well as soils characterised by hardpans occur within the profiles. Furthermore, heavy duplex soils occur in some areas, e.g. where salinity is present in the subsoil, implying that the soil can only be utilised by means of ridges. Along the Olifants and Orange River the alluvial soils are characterised by layering and at higher altitudes by varying degrees of lime accumulation and hardening. Along the lower course of the Orange River large areas of the so called “ghom” material are already utilised. The latter was initially physically weathered, brittle “gneiss”, but due to the actions of soil preparation it has been turned into “soil”. The soils on which table grapes are grown in Limpopo vary according to the parent material

FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY | 29

– sedimentary material, weathered granite or dolomite, which have given rise to deep, fertile yellow to red soils. Almost without exception, these soils require physical rectification, with South Africa being unique in this regard, on account of drastic deep cultivation actions being used. At the same time, this also offers an opportunity for rectification of any possible chemical deficiencies, through the addition of suitable ameliorants in the right quantities. Except for the Orange River, most of these soils are characterised by low phosphorus (P) contents, and in many cases (except for the Lower Orange River area) also by excessive soil acidity. In exceptional cases soil acidity may be the result of hydrogen (H + ) ions, derived from high organic matter content of the specific soils, typical for those with fynbos origin. These H-ions are not detrimental, but may disturb the accessibility of specific nutrients, and the general nutrition of non-acid loving plants, like the grapevine. More serious limiting soil acidity is caused by the loss of basic cations, due to advanced weathering of clay minerals and leaching, with the vacated positions then being taken by the omnipresent H-ions, thus disintegrating the clay mineral on which it is adsorbed, giving rise to the release of aluminium (Al) ions. These Al-ions generate more H-ions, resulting in a further reduction of soil pH. At high concentrations aluminium is also toxic to root growth and functioning, thus disturbing general nutrition. CORRECTI ON OF SO I L AC I D ITY Since lime moves very slowly in most soils, soil preparation is the only opportunity for adequate application. In contrast to P (to be discussed), the ultimate aim of lime application is to rectify soil pH, as homogeneously as possible to a depth of at least 1 000 mm, thus making it possible for roots to utilise a large soil volume unhindered, to buffer the grapevine against climatic shocks. The coarse fraction of the soil must be considered, in order to prevent excessive lime applications. The pH does not give an indication of the lime requirement. Rather, lime requirement is dictated by the exchange capacity of the soil and the extent up to which it is occupied by hydrogen – and aluminium ions. For table grapes, the well proven Eksteen-method (Eksteen, 1969) is proposed for calculation of lime requirements. This method utilises the general exponential relationship between soil pH and the H saturation level of the soil, as represented by the so-called R-value , i.e. the Ca+Mg/H relationship. For vineyards the desirable pH of 5.5, measured in KCl, is targeted (Conradie, 1983), which corresponds an R-value of 10. The following formula may be used to calculate the lime requirement of of a soil, down to a depth of 150 mm:

Lime requirement (ton ha –1 /150 mm) = [(H x 10) – (Ca + Mg)] x 4/11 where H, Ca and Mg are imported as cmol kg –1

Experience has however shown that for soils with high magnesium (Mg) content, this formula under calculates the lime requirement because in comparison to Ca, the Mg

30 | CHEMICAL CORRECTION OF SOILS DURING SOIL PREPARATION