Effect of different land covers on nitrate-nitrogen leaching and nitrogen uptake in Iowa

Abstract

Nitrate-nitrogen (NO3-N) loading from subsurface drainage is an environmental concern in the Midwest. The majority of NO3-N loading occurs in April, May and June when the crops are not planted or just establishing. In this study, NO3-N leaching was monitored under alternative land covers and in a corn-soybean rotation. Land cover treatments in a 2-year field experiment included: 1) corn-soybean rotation initiated with corn in 2006 and fallow in late fall and early spring (fallow-Corn-fallow-Soybean, fCfS); 2) corn-soybean rotation initiated with soybean in 2006 and fallow in late fall and early spring (fallow-Soybean-fallow-Corn, fSfC); 3) corn-soybean rotation initiated with corn in 2006 with rye cover crop (rye-Corn-rye-Soybean, rCrS); 4) corn-soybean rotation initiated with soybean in 2006 with rye cover crop ( rye-Soybean-rye-Corn, rSrC); 5) Corn with established kura clover as a living mulch (kura-Kura-kura-Corn, kKkC); and 6) Pasture as a perennial grass treatment (PP). Subsurface drainage volume and NO3-N concentration were monitored. Suction lysimeters were installed to extract the soil water solution for NO3-N analysis. Biomass of spring cover crops was sampled to analyze nitrogen (N) content. The objectives of this study were: 1) to determine NO3-N loss through subsurface drainage as affected by different land covers; 2) to investigate the NO3-N concentrations in the soil water under different land covers and 3) to quantify the nitrogen uptake by different cover crops in the spring. The results from the two-year study indicated that the annual average NO3-N loss for fCfS and fSfC treatments was 37.5 kg N ha-1 and that the rCrS and rSrC treatments reduced NO3-N leaching by 3.8 kg N ha-1 during April, May and June. kKkC and PP treatments resulted in 39.7% and 59.9% annual NO3-N leaching reduction, respectively, when compared to the average NO3-N loss of fCfS and fSfC treatments. Rye followed by soybean reduced the NO3-N concentration in the soil solution significantly (56.4%) at the 30- and 60-cm depths, and PP treatment showed the lowest NO3-N concentration at those two depths. The average nitrogen uptake by rye was 33.3 kg N ha-1 at growth termination, and the average N uptake was 59.9 kg N ha-1 for kura clover and 33.2 kg N ha-1 for pasture in early June. This study suggested that winter rye cover crop, kura clover as a living mulch and perennial pasture land covers have positive effects on NO3-N loss reduction under the weather condition encountered during this study period in Iowa.