Growth analysis of dry matter accumulation and N uptake of forage maize cultivars affected by N supply

The productivity of eight forage maize cultivars (Zea mays L.) in response to N was investigated in a 3-year held experiment located in Northern Germa ny. Nitrogen fertilizer applications were zero, 50 and 150 kg N/ha given ea ch year shortly after sowing. Each cultivar was grown on the same plot, beg inning in 1993, following the ploughing up of a 2-year old grass sward, to which slurry had been added. Plants were sampled regularly for dry matter ( DM) production and N uptake. A non-linear regression equation was used to c ompare the data. Growth analysis and N uptake characteristics (maximum crop growth rate, duration of maximum crop growth rate, period until maximum cr op growth rate, maximum N uptake rate, duration of maximum N uptake rate, p eriod until maximum N uptake rate) which derived from the function were use d to compare the cultivars. The cultivars DM yield and N uptake were highest in 1993 and declined in th e next two years partly due to a decrease in soil N mineralization followin g the ploughing of the grass sward and partly due to the drier weather cond itions during the summers of 1994 and 1995. Duration of the maximum crop gr owth rate was greater during the cool year of 1993. In contrast, maximum cr op growth rate was at its highest in the dry vegetation period of 1995. A s ignificant N x cultivar interaction for growth analysis characteristics (P < 0.05) was found in 1995. Cultivars with a high maximum crop growth rate ( above the average value of the eight cultivars tested) and a short duration of maximum crop growth rate (below the average) accumulated more DM than t hose genotypes which showed an inverse relationship. Increasing N yield was determined by increased maximum N uptake rather than by a greater duration of maximum N uptake. A significant N x genotype inte raction for N uptake parameters (P < 0.05) was found in 1994 and 1995. With some exceptions, cultivars with a high maximum N uptake rate (above averag e) accumulated more N per unit area compared to those genotypes which had l ow uptake rates. The exceptions had a longer duration of uptake, which coul d not, however, compensate for the lower rate. Maximum N uptake rate occurr ed earlier and duration of maximum N uptake rate increased compared to the start and duration of maximum crop growth rate. Especially in 1995, the amo unt of N taken up before the day of maximum crop growth rate accounted for 71 % of total N uptake. The N uptake rate and the amount of accumulated N u ntil the day of maximum crop growth rate were highly correlated with DM yie ld. This result indicates the availability of genotypic Variability in crop gro wth and N uptake rate to assist the improvement of DM yield by selection.