Effects of nitrogen fertilization and irrigation rate on grain yield, nitrate accumulation and nitrogen balance on sandy farmland in the marginal oasis in the middle of Heihe River basin EFFECT OF NITROGEN RATES ON NO3--N ACCUMULATION AND NITROGEN USE EFFICIENCY UNDER MAIZE AND WHEAT INTERCROPPED SYSTEM Effects of nitrogen fertilization on protein components contents and processing quality of different wheat genotypes Effects of Nitrogen Rate on Assimilate Transportation to Underground at Different Maize Growing Stages