Nutrient management strategies for sustainable crop production in acid soils: the role of research using isotopes

Malaysian agriculture thrives on 6.3 million hectares of land, mainly on highly leached acidic soils. These soils are inherently infertile due to nutrient deficiencies, especially of N, P, K, Ca and Mg, and / or heavy metal toxicities, mainly AL and Mn. Correcting these constraints with proper soil management measures can yield productive and sustainable farming systems. Improved management procedures in these systems must emphasize greater reliance on organic nutrient sources and the judicious use of inorganic fertilizers. This is especially for N, and P, as overcoming deficiency in these nutrients usually generates the greatest improvements in crop yields. Although there is fairly good understanding of the management of inorganic N and P fertilizers for crop production in acid soils, much less information is available on the management of organic forms of these nutrients, while data on interactions of the two forms is very much limited. Understanding the underlying processes in these strategies using conventional methods is most often difficult, but isotopes have been found to be useful in unraveling the mechanisms associated with nutrient availability, fertilizer use efficiency, losses and residual effects, as well as the role of legumes in farming systems. Also isotopes are important for monitoring soil moisture movement and availability, and in identifying varietal differences in nutrients use efficiency. Radioactive isotopes such as 32P, 33P, 35S and 3H have been used in studies on fertilizer use efficiency, nutrient management, root activity and water availability, whilst stable isotopes (15N, 13C) can provide valuable information on functions of ecosystems, organic matter dynamics and other N and C transformations.

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