Hidden nutrient leaks in agricultural soils: the case of grain residues and losses.

Abstract More accurate nutrient balances are a key tool for keeping soils healthy and land use sustainable. In Argentina, though, they evolved towards a "black box" simplified concept with two main components: input of nutrients through mineral fertilization and output via grain harvest. However, this simplification underestimates nutrients' extraction through grazing, biomass harvesting, residues, and losses during grains' storage and transport. The study proposes an extended nutrient balance equation, and estimates the proportion of N, P, K and S extracted from soils in these unaccounted factors for 12 grain crops in the period 2009-2019. Compared with previous studies, estimated extraction rates are at least 46% higher for N; 25% for P and 176% for K for the five main crops. Grain production figures showed to be good indicators of extracted nutrients in oilseeds but not in cereals, mainly due to an increased proportion destined for cattle in feed-lots. The amounts of potentially recyclable nutrients contained in secondary storage losses and residues represent 8% of the total N and 43% of the total K2O applied per year for all crops in Argentina. A circular economy approach to grain cleaning and storage operations could show ways to recover and recycle these residues and losses, and constitute a promising strategy for developing more resilient and productive soils.