The mobility and transformation of soil nitrogen and the relationships between soil and plant nitrogen and yield at different times following application of various nitrogen fertilizers to sweet corn

摘要

The concentration of NH4-N, NO3-N and their sum (mineral N) were monitored 12 times in n1 or 2 weekly intervals in the soil under a sweet corn crop. The samples were taken on the nfertilizer band and to depths of 200, 400 and 600 mm. The NO3-N concentration of the sap nexpressed from the midrib of the leaf opposite and immediately above the primary cob (sap nNOS-N) and that of midrib dry matter (midrib N03-N) were determined weekly. nUnder the low rainfall and optimized irrigation of this trial the concentration of mineral N nin soil to the depth of 400 mm or more was a good predictor of yield response to application nof N at 10 of the 12 sampling times. The concentration of either NH4-N or N03-N in the soil nto any depth and the concentration of mineral N in the surface 200 mm correlated with the nyield at only a few times of sampling. The concentration of mineral N in the top 200 mm of nsoil 1 or 2 weeks after top-dressing of N was highly correlated to yield. nThe concentration of sap NOS-N and midrib NO3-N decreased continuously until harvest. nBoth these concentrations were significantly correlated with the rates of basal and top-dressed nN in most sampling times. These were also strongly correlated to yield 1 or 2 weeks after N ntop-dressing. nAmmonium sulfate, ammonium nitrate and urea gave similar responses in sap NOS-N and nmidrib NOS-N and in soil nitrogen after 5 weeks when nitrification of fertilizer NH4-N was ncomplete. These observations indicated that soil mineral N, sap NO3-N and midrib NOS-N nall offer potential as techniques to predict the yield response of sweet corn to N application. nThe sap NO3-N test was simpler, quicker, cheaper and more consistent than other tests. rotations, and (b) the use of mixtures to select medics suitable for such rotations.