Effects of Tillage Type and Nitrogen Rate on Corn Hybrids in Western Nebraska.

Understanding interactions between different tillage types and N application rates is essential in selecting best management practices that optimize utilization of water and nutrient resources. Field studies were conducted at North Platte, NE in 2011 and 2012 and Gothenburg, NE in 2012 to determine the effects of conventional-, strip- and no-till practices and nitrogen (N) rates (0, 84, 164, 252 kg/ha) on crop yield of corn hybrids recommended for semiarid climate of western Nebraska. The interactions between tillage type and nitrogen rate were analyzed with qualitative (tillage type) vs quantitative (N rate) polynomial regression equations. The most parsimonious statistical model (optimal set of regression parameters) was selected using backward selection. Results showed that increase in N rate did not affect response of crop yield under different tillage types; with adding each kg of N yield linearly increased by 0.02 t/ha and quadraticaly decreased by -0.00003 t/ha. Negligibly small estimate of quadratic term indicates that crop yield would reach a plateau if N rates >252 kg/ha were used in this in this experiment. Among three tillage types, conventional tillage yielded 0.5 t/ha more than strip- and 1.1 t/ha more no-till, regardless of N rate (differences in intercepts). We suspect that such yield differences in tillage types and most likely the consequence of: (1) large year/location variation; (2) earlier and more uniform crop emergence, better early season growth and crop canopy establishment; and (3) high irrigation rates, which did not allow for water stress that would favor growing conditions under no-till practices. To come up with tillage recommendations in western NE, long term experiments that would account for large year to year variation and quantify the difference between conventional-, strip- and no-till under irrigated and rain-red conditions need to be conducted.