INTERACTIONS OF TRAFFIC AND TILLAGE APPLIED TO COTTON ON N-MOVEMENT BELOW THE ROOT-ZONE OF A SUBSEQUENT WHEAT CROP

Although research has demonstrated the negative impact of traffic-indu ced soil compaction on crop productivity, knowledge is lacking regardi ng the interactive effects of equipment traffic and tillage systems, e specially in regards to N management in conservation-tilled multiple-c ropping systems. The objective of this study was to examine the intera ction of traffic and tillage systems applied to cotton (Gossypium hirs utum L.) on N utilization and movement below the root zone of subseque nt double-cropped wheat (Triticum aestivum L.). A field study was init iated in 1987 on a thermic Typic Hapludult soil complex, utilizing a w ide-frame tractive vehicle (WFTV) that allows for 6.1-m wide, untraffi cked research plots to double-crop cotton with wheat. The experimental design was a split-plot with three replications. Main plots were: (1) conventional traffic (simulated with tractor); (2) no traffic (WFTV o nly). Subplots were tillage systems for cotton: (1) complete surface t illage without subsoiling (surface); (2) complete surface tillage and annual in-row subsoiling to 40-cm depth (subsoil); (3) complete surfac e tillage with once-only complete disruption of the tillage pan by sub soiling to a 50-cm depth on 25-cm centers in 1987 (complete); (4) stri p-till where cotton was planted with in-row subsoiling into wheat resi due. All tillage treatments were applied to the cotton and residual ef fects were observed in the wheat. In 1990-1991, fertilizer application s were made to wheat as N-15-labeled NH4NO3, and soil solution samples were collected (90-cm depth). While previous cotton tillage had no si gnificant effect on wheat yields, traffic reduced wheat yields from 34 27 to 2981 kg ha(-1) in 1990. With no traffic, total fertilizer N reco very in the plant-soil system was increased by 20 and 10% in 1990 and 1998, respectively. The strip-till tillage treatment increased total f ertilizer N recovery in wheat by 20% compared with other tillage syste ms in 1990. Surface tillage without subsoiling for cotton increased NO 3-N concentration below the root zone of wheat (90-cm depth) in both y ears. The data indicate that the tillage/traffic management system use d for production of one crop in a double-cropping system was a major f actor in reducing N losses and increasing fertilizer N recovery in the plant-soil system of the succeeding crop.