Alternate irrigation and fertilization to reduce leaching of nitrates

A combination of alternate row furrow irrigation (ARFI) and alternate fertilizer application was tested in a two years study to evaluate whether this management strategy would reduce the leaching of nitrates. The study was carried out in a 6.25 ha corn field (Cozad-Hord fine silty, Typic Haplustolls) at the WCREC in North Platte, NE. The nitrogen (N) rates studied were uniform application at the recommended rate (R) and a reduction of 25% of R. Increased fertilizer use by isolating N from irrigation water and reduced NO3-N leaching was expected under ARFI. There were no differences in yield between ARFI and every row furrow irrigation (ERFI) in 1997 and 1998. The R rate produced 0.2 Mg ha–1 corn grain yield in 1997 but in 1998, both N rates yielded the same. Spatial variability of soil organic matter (SOM) and water drainage explained grain corn yield variation. The NH4-N disappearance was faster under ERFI than ARFI, but included the effect of double N concentration applied in ARFI. Chlorophyll meter readings (SPAD 502) were 5 and 2.8% higher under ERFI than ARFI in 1997 and 1998 respectively, but yield was not affected. A conservative tracer (KBr) was applied before the first irrigation to imitate the NO3-N movement. Br recovery values under ARFI were twofold of ERFI. The ARFI relative Br– peak movement during the growing season was 0.15 m and 0.60 m under ERFI. After harvest Br– moved to 0.60 m in ARFI and 1.22 m in ERFI. Differences in Br– movement between water inflow and outflow positions in the furrow were from 0.15 m to 0.60 m under ERFI. Differences in Br – movement between replications suggested preferential flow in the west side of the field. Rendered images corroborated the features of the conventional graphics and described the Br– distribution. Br– and residual NO3-N images shared the same spatial distribution. No correlation was found between soil Br– and NO3-N samples collected during the growing season