TILLAGE AND NITROGEN PLACEMENT EFFECTS ON NUTRIENT-UPTAKE BY POTATO

Deep tillage of compacted soils can improve potato (Solanum tuberosum L.) tuber yield and quality if no other production factors are limitin g. We hypothesized that within-row subsoiling and N placement would af fect tuber yields and availability of plant nutrients. Potato (cv. Rus set Burbank) was grown after winter wheat (Triticum aestivum L.) in 19 89 and after dry bean (Phaseolus vulgaris L.) in 1990 on a furrow irri gated Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calc iorthid). Fall tillage treatments (disking, chiseling, and mold-board plowing) were split with zone subsoiling after planting. Nitrogen was broadcast before planting or banded beside the seed piece at planting across all tillage combinations. We estimated plant nutrient status an d uptake each year with whole-plant and petiole samplings during tuber growth. Final tuber yield and quality were determined in early Octobe r. Fall tillage did not influence nutrient concentration and uptake, t uber yield, or quality. Zone subsoiling increased average plant dry we ights 9%, total tuber yields 10% (4 Mg ha(-1)), and quality, and incre ased P uptake an average of 11.6% (1.8 kg P ha(-1)) without appreciabl y changing whole-plant or petiole P concentrations. Banding N increase d average plant dry weight 6.4%, total tuber yield 9%, and N uptake 28 % compared with broadcast N. Petiole NO3-N, P, K, and Zn concentration s were higher where N was banded. There were no consistent zone subsoi ling x N placement interactions. Higher nutrient applications may be r equired with zone subsoiling or to compensate for soil compaction prob lems.