Nitrate Leaching under Furrow Irrigation as Affected by Crop Sequence and Tillage

The potential for NO 3 ‐N leaching after alfalfa ( Medicago sativa L.) in irrigated crop production depends on cropping sequence and tillage practices. A 2‐yr field experiment in south‐central Idaho compared the NO 3 ‐N leached following alfalfa of a conventional tillage bean‐bean ( Phaseolus vulgaris L.) rotation with a silage corn ( Zea mays L.)‐winter wheat ( Triticum aestivum L.) rotation in a conventional tillage or no‐till system. Nitrate leaching was determined by: (i) sampling the soil solution below the root zone (1.2 and 1.5 m) using ceramic‐tipped samplers and calculating the N movement from the water balance, and (ii) measuring the change in soil NO 3 ‐N at 1.35 to 4.5 m from soil samples taken in the fall and spring to 4.5 m. During the second growing season, average soil solution NO 3 ‐N concentrations (below the root zone) were 28, 4, and 10 mg L −1 for the bean‐bean, corn‐wheat no‐till, and corn‐wheat tilled treatments, respectively. The soil NO 3 ‐N in 1.35 to 3.3 m at the end of the study was 80 kg N ha −1 higher for the bean‐bean treatment than for the corn‐wheat treatments. The NO 3 ‐N that moved below 1.35 m during the 2 yr was 53 kg ha −1 higher for the bean‐bean than for the corn‐wheat treatments. The soil NO 3 ‐N in the 1.35 to 3.3 m depth after 2 yr was 21 kg ha −1 higher for the corn‐wheat under conventional tillage than under the no‐till system.