Can we reduce phosphorus runoff from agricultural fields by stimulating soil biota?

When fertilizer phosphorus (P) is applied to soils, the P can run off fields and cause harmful algal blooms. Due to its chemistry, much of the added P that does not run off can bind to soil particles and become inaccessible to plants. In natural systems, microbial and faunal decomposers can increase soil P accessibility to plants. We tested the hypothesis that this may also be true in agricultural systems, which could increase P application efficiency and reduce runoff potential. We stimulated soil fauna with sodium (Na ) and microbes with carbon (C) by adding corn (Zea mays L.) stover and Na solution to plots in conventionally managed corn fields in northwestern Ohio. Stover addition increased microbial biomass by 65 ± 12% and respiration by 400-700%. Application of stover with Na increased soil detritivore fauna abundance by 51 ± 20% and likely did not affect the other invertebrate guilds. However, soil biological activity was low compared with natural systems in all treatments and was not correlated with instantaneous measures of P accessibility, though cumulative P accessibility over the course of the growing season was correlated with microbial phosphatase activity (slope = 1.01, p < .01) and respiration (slope = 0.42, p = .02). Therefore, in agricultural systems, treatments to stimulate decomposers already in those systems may be ineffective at increasing soil P accessibility in the short term, but in the long term, higher microbial activities can be associated with higher soil P accessibility.