A simplified test of cornstalk nitrate for better N management

Abstract

The end-of-season test for cornstalk nitrate gives site-specific information about crop N sufficiency and N excess. It is a very valuable decision tool for increasing the sustainability of N fertilizer practices. However, little information is available about the possibility of simplifying this tissue test and the extent to which results of the test are influenced by deviations from recommended sampling procedures. This information would be very valuable to promote the acceptance and use of the test by maize growers. Here we analyzed stalk nitrate concentrations from stalks collected in several experimental maize plots receiving different rates of N fertilizer ranging from deficient (zero nitrogen) to excess (350 kg N ha−1). Our results show that nitrate concentrations of 2.5-cm segments of stalk with and without nodes showed no significant differences, and no special care during stalk sampling must be taken. In addition, although NO3-N concentrations in pith tissue are, on average, 29% higher than in the rind, the relative amounts of nitrate in pith (18%) and rind (82%) revealed little need for efforts to ensure that the ratios of pith and rind were not altered during sampling or analysis. Nitrate concentrations tended to decrease by 4% for each cm of deviation above the height normally sampled. Overall, the results presented indicate the robustness of the test to small deviations during sampling procedures and that a minimum of 10 stalk segments are necessary to adequately assess N sufficiency. Finally, it is feasible to decrease the length of the sampled stalk to segments of 4 cm if they are centered about 25 cm from the ground, to avoid large deviation due to the stem nitrate gradient observed. Our findings can help to promote and simplify the cornstalk nitrate test, improving N management and decreasing the negative environmental impact of excessive fertilizer applications.