Paper Title
QUANTIFICATION OF NUTRIENT FLOWS AND BALANCE IN CROP FIELD IMPROVES AGRICULTURAL SUSTAINABILITY WITH LOWER ENVIRONMENTAL FOOTPRINT

Abstract
Lack of a holistic understanding of the rate and fate of nutrient flows in agroecosystems is a constraint to sustainable soil fertility management limiting the achievement of food security. Nitrogen (N), phosphorus (P), potassium (K) and sulfur (S) losses from and gains to the field were measured for two consecutive years in a maize field in Floodplain soils. The experiment consisted of:(i) two levels of residue (NR, no residue vs. CR, 30 cm residue) and (ii) four levels of fertilizer (control [CL]; farmers’ practice [FP]; recommended dose [RD; 225, 60, 80 and 30 kg N, P, K and S ha-1]; and 125% of RD [125RD]). Nutrient leaching was a significant pathway accounting for 3-4, 6-8, 7-8 and 1.5-2% of total N, P, K and S fertilizer. Volatilization, denitrification and leaching caused 27-37, 5-7 and 4-5% loss of the applied N. Volatilization was 7.5% higher in RD with CR than in RD without CR. The N, P, K and S addition through irrigation and rainfall ranged 2.9-5.1, 2.4-4.2, 3.2-5.7 and 2.6-5.1 kg ha-1, respectively. CR integration with fertilizer rates significantly improved soil nutrient balances which exhibited significant positive relationships with the total nutrient contents in soils. The positive nutrient balance enhanced nutrient buildup in soils while the negative indicated nutrient mining. Addition of CR with RD resulted in a positive balance for P and S by 22 kg P ha-1 and 13 kg S ha-1. A 25% increase in N and K and 25% reduction in P and S coupled with 30 cm CR incorporation reduced excessive P and S application while reducing the negative N and K balances. Estimation of a holistic input-output balance suggests whether the fertilizer rate is inadequate or surplus or if it maintains soil fertility for sustainable crop production and environmental footprint.