SIGNIFICANCE OF NUTRIENTS UPTAKE MECHANISMS IN CROPPING SYSTEMS

摘要

Sustainable crop production will obviously require enhanced flows of nutrients to crops, which in turn comprises higher amounts of nutrient reserves in soils and higher nutrient uptake and utilization by crops. Productivity of current cropping systems and protection of environmental quality cannot be sustained for long if practices such as excessive or under application of nutrients and inefficient utilization of crop residues and wastes are continued. To achieve this goal, it is necessary to quantify measurable sustainability indicators such as: levels of available nutrients, organic compounds (carbon, N, and P etc.), soil microflora and fauna, nutrients lost through runoff and leaching, and the rates of change in those variables as affected by specific nutrient management practices in cropping systems. It is not difficult to obtain those indicators with present technology. However, it is difficult to correctly evaluate the contributions of those indicators to the productivities of crops. Crops plants have recently revealed to acquire plant nutrients with different mechanisms. Soils high in Fe-P may be suitable for pigeonpea with special mechanism to utilize Fe-P. However, for crops without such a mechanism like sorghum and maize, soils high in Fe-P is undesirable. Likewise, AM population density in soil has significant meaning for mycorrhizal corps, but is meaningless for non-mycorrhizal crops. Such ndicators and their responses are likely to vary with each cropping system due to a multitude of interactions among soils and crops in diverse climates. Design and development of comprehensive nutrient management plans for various cropping systems will also require not only knowledge on plant nutrition mechanisms, but also require an integrated knowledge to understand processes occurring in various cropping systems. Research initiatives for sustainable nutrient management at the level of the cropping system must be conceived, therefore, on the basis of a holistic understanding of interactions among production, environmental, and biological components.