Incorporation of post–harvest or green manure crop residues influences soil P mobilization and P nutrition of wheat

[Truncated] Crop residues are valuable source of organic matter and reservoirs of plant nutrients. Efficient recycling of nutrients from crop residues depends on soil and crop residue management, contributing to sustainability in cropping systems. With the supply of P fertilizer raising questions about a potential future crisis in crop production, recycling P through crop residues is an important component of P nutrient management in agriculture. Crop residues could replace or at least minimize the inorganic P fertilizer requirement in crop production depending on the nature of soil, crop residues, cropping systems and management practices. However, understanding the soil P dynamics as influenced by a crop residue amendment would underpin strategies to improve P recycling by effective crop residue management. Hence, the major focus in this study was to (i) characterize the P pools in soil after incorporation of crop residues varying in P quality and quantity; and (ii) determine the effect of soil incorporation of post-harvest (dry) or green manure crop residues on wheat P nutrition.
Green manuring, a practice of incorporating crop vegetative biomass as fresh, could provide better P nutrition to the subsequently-grown crops because fresh residues contain more readily-available P than dry residues. Also, fresh crop residues are considered of better quality because drying the residues leads to loss of nutrients (eg. dissolved P) and alters the P fractions in crop residues. A soil incubation study was conducted to (i) compare P release from green manure or dry crop residues (70 DAS) high in P content but varying in quality; and (ii) characterize the temporal variation in soil P pools with decomposing crop residues. Incubation of fresh crop residues resulted in an increase in pH, microbial respiration rate and P availability in soil. Phosphorus was more available from fresh than dry residues, especially early in the incubation period. Soil incorporation of crop residues as fresh (i.e. green manuring) improved biological cycling of soil P in comparison with dry residues. Hence, green manure crops could increase P availability to the subsequently-grown crops, thus enhancing productivity and soil fertility.