EFFECT OF PLANTING DATE ON TIME AND RATE OF NITROGEN ACCUMULATION BY MAIZE (ZEA-MAYS L)

Effects of environment on time and rate of nutrient accumulation by crops affects fertilizer nutrient use efficiency. The effect of planting date on rate, time and amount of nitrogen (N) accumulated by maize from a Hamerly cl soil (Aeric Calciaquoll) was examined with and without supplemental irrigation. Maize was planted on three dates spaced at 2‐to 3‐week, intervals; the earliest planting date was 1 May in 1984 and 1985. N accumulation was examined as uni‐ and diphasic tanh[k(time)] functions and solved for total N accumulation at harvest, time of maximum N accumulation rate and the time coefficient of N accumulation. A diphasic function, which indicates two periods of intense N accumulation, provided the closest agreement with observed N accumulation. As planting was delayed, time required to reach maximum N accumulation rates, τ (uniphasic) or τ1 and τ2 (diphasic), decreased from an average of nearly 75 to 42 days (uniphasic) and from nearly 65 to 35 days and 100 to 75 days after planting for τ1 and τ2, respectively. Maximum N accumulation rates increase from about 59 to 75 mg N plant−1 day−1 (uniphasic) or 35 to 65 mg N plant−1 day−1 and 20 to 70 mg N plant−1 day−1 for the first and second maxima in the diphasic model, respectively. Average maximum total N accumulation ranged from 2.85 g N plant−1 for early plantings to 1.5 g N plant−1 for plantings made on 25 June. The time coefficient, k (uniphasic) or k1 (diphasic), tended to increase from average values of about 0.04 to > 0.09 day−1 for k and from about 0.04 to > 0.105 day−1 for k1. The second time coefficient, k2, of the diphasic function varied widely between about 0.075 to > 0.12 day−1 and showed complex relationships with planting date. Periods of N accumulation shortened and intensity of N accumulation increased as the time coefficient increased. Copyright © 1990, Wiley Blackwell. All rights reserved