FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 6

ROCK PHOSPHATE Soft rock phosphate products with P concentrations varying between 14 and 16% are available. Soft rock phosphate is mined from sedimentary formations (Apatite-calcium- phosphate) and contains P in varying concentrations (between 3% and 16%). It also contains Ca (30 – 40%) and it is therefore specifically suited for use on soils with low pH values, where the Ca-oxide helps to raise the soil pH. These products are suitable for P rectifications during soil preparation and are allowed in most organic systems. However, producers should take the defining factors into account, when they must decide on the P source to be used. MULCHES AND COVER CROPS Even though mulches are not part of the fertilisation programme, it nevertheless forms part of the general soil care programme that must be maintained annually. If fresh organic material with a high C:N ratio is used as mulch at the start of the season, the N fertilisation should be increased by approximately 10% in order to compensate for the N that is used in the microbiological degradation process of the organic material. The advantages of mulches are not handled here, but the following aspect must, however, be highlighted. Mulches increase the organic content of the soil and, in conjunction with this, the microbial activity in the topsoil. This leads to the increased development of a network fine roots in this zone. These roots play an important role in the assimilation of nutrients but are exposed to large fluctuations in moisture and temperature. The protection and maintenance of these roots through correct irrigation scheduling, specifically during the last part of the season – including post-harvest – is important in order to ensure continuous nutrient uptake. Mulches play an indirect role in the fertilisation programme, on account of contributing to the general improvement of soil health, in the following ways: • Elevation of the organic content of the soil – this stimulates microbial activity and raises the soil’s capability to hold on to water and nutrients. • Protection of the soil surface – better water infiltration, less fluctuation of soil temperature. • Provision of plant nutrients – slow release of nutrients through the mineralisation of the organic material, and N by means of the N binders like medics, clover and serradella. • Elevation of the biodiversity of the system – this happens through crop rotation and combinations of different cover crops. In order to unlock the advantages of cover crops, correct management is important in terms of seedbed preparation, fertilisation and crop rotation.

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