| Crop residues and biofertilizers are primary sources of nutrients for organic crop production.
However, soils treated with large amounts of nutrient-enriched manure have elevated
phosphorus (P) levels in regions of intensive animal agriculture. Surpluses occurred in these
amended soils, resulting in large pools of exchangeable inorganic P (Pi) and enzyme-labile
organic P (Po) that averaging 30.9 and 68.2 mg kg-1, respectively. Organic acids
produced during crop residue decomposition can promote the complexation of
counter-ions and decouple and release unbound Pi from metal and alkali metal
phosphates. Animal manure and cover crop residues also contain large amounts of
soluble organic matter, and likely generate similar ligands. However, a high degree of
heterogeneity in P spatial distribution in such amended fields, arising from variances in
substrate physical forms ranging from slurries to dried solids, composition, and diverse
application methods and equipment. Distinct clusters of Pi and Po were observed, where
accumulation of the latter forms was associated with high soil microbial biomass C and
reduced phosphomonoesterases’ activity. Accurate estimates of plant requirements and
lability of soil P pools, and real-time plant and soil P sensing systems are critical
considerations to optimally manage manure-derived nutrients in crop production
systems. An in situ X-ray fluorescence-based approach to sensing canopy and soil
XRFS-P was developed to improve the yield-soil P relationship for optimal nutrient
recommendations in addition to allowing in-the-field verification of foliar P status. |