Abstract
Worldwide, arable soils have been degraded through erosion and exhaustive cultivation, and substantial proportions of fertilizer nutrients are not taken up by crops. A central challenge in agriculture is to understand how soils and resident microbial communities can be managed to deliver nutrients to crops more efficiently with minimal losses to the environment. Throughout much of the twentieth century, intensive farming has caused substantial loss of organic matter and soil biological function. Today, more farmers recognize the importance of protecting soils and restoring organic matter through reduced tillage, diversified crop rotation, cover cropping, and increased organic amendments. Such management practices are expected to foster soil conditions more similar to those of undisturbed, native plant-soil systems by restoring soil biophysical integrity and re-establishing plant-microbe interactions that retain and recycle nutrients. Soil conditions which could contribute to desirable shifts in microbial metabolic processes include lower redox potentials, more diverse biogeochemical gradients, higher concentrations of labile carbon, and enrichment of carbon dioxide (CO2) and hydrogen gas (H2) in soil pores. This paper reviews recent literature on generalized and specific microbial processes that could become more operational once soils are no longer subjected to intensive tillage and organic matter depletion. These processes include heterotrophic assimilation of CO2; utilization of H2 as electron donor or reactant; and more diversified nitrogen uptake and dissimilation pathways. Despite knowledge of these processes occurring in laboratory studies, they have received little attention for their potential to affect nutrient and energy flows in soils. This paper explores how soil microbial processes could contribute to in situ nutrient retention, recycling, and crop uptake in agricultural soils managed for improved biological function.
Highlights
Native soil ecosystems have been converted for agricultural use since the dawn of human civilization
This paper explores how soil microbial processes could contribute to in situ nutrient retention, recycling, and crop uptake in agricultural soils managed for improved biological function
Some bacteria reduce NO3− to NH4+ (Figure 2) in a process known as dissimilatory nitrate reduction to ammonium (DNRA)
Summary
Native soil ecosystems have been converted for agricultural use since the dawn of human civilization. Modern agriculture is dominated by large-scale, continuously mono-cropped fields that have incurred significant losses of soil and organic matter and require increasing amounts of fertilizers [2,3]. Continuous agriculture precludes most plant residues from being returned to the soil, and repeated tillage further depletes soil organic matter through physical disruption and oxidation [9]. Crop rotations and cover cropping introduce a wider variety of organic compounds through greater root densities. Such management practices could foster adaptive microbial diversity in soils for better nutrient reutilization and fewer losses to the environment [13]. This paper highlights beneficial microbial metabolisms that could become more operational once soils are no longer subjected to intensive tillage and organic matter depletion.
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