South Africa Wine Technical Yearbook 2025

DECEMBER

SHUTTERSTOCK

Soil texture’s influence on soil biological health indicators – implications for vineyard management By Dr Roeline van Schalkwyk & Prof Ailsa Hardie-Pieters

Carbon and nitrogen cycling indicators Carbon (C) and nitrogen (N) cycling is the engine of soil fertility, driven by microbial processes. Key indicators measure the organic pools of these nutrients that fuel microbial life and are, in turn, made available to the vine. � Soil organic C (SOC): This is a key indicator of soil health as it serves as the energy source (food) for soil fauna. Fine-textured soils, with their high specific surface area, can store more SOC through the formation of protective organo-mineral complexes. Conversely, the larger pores in coarse-textured soils facilitate faster decomposition. • Permanganate oxidisable carbon (POXC): Historically, the POXC test has been interpreted as a measure of the ‘labile’ or ‘active’ soil carbon fraction – a readily available microbial food source. However, recent research compellingly shows this interpretation is incorrect.

Introduction In modern viticulture, assessing soil health is becoming a practical management tool, providing critical data for optimising inputs and enhancing vineyard sustainability. However, interpreting soil health analyses can be complex. The physical properties of a soil, especially its texture, have a profound effect on the biological potential and function. While soil management practices are crucial, soil texture dictates their effectiveness. Understanding how texture affects soil biological indicators is essential for correctly interpreting soil health test results and developing effective, site-specific strategies. This article reviews the interaction between soil texture and key soil health biological indicators.

77

TECHNICAL YEARBOOK 2025