Effect of weather, forecrop and intensity of nitrogen fertilization on maize grain yield and its structure

The results of polyfactorial field trials in Borovce locality obtained in years 1998-2002 were evaluated from the point of view of the influence of weather conditions in the years, different crop rotation (spring barley and winter wheat) and fertilization intensity on maize (Zea mays L.) grain yield and its yield components (number of spikes per square meter, grain weight on spike and one-thousand grain weight - TGW). The trials are situated in the water protected area at Borovce near Piestany (western part of the Slovak Republic) in a maize production zone (altitude 167 m) on a medium heavy textured soil (Haplic chernosem in a loam), where average annual temperature is 9.2 deg C (during vegetation period 15.5 deg C) and average annual precipitation is 593 mm (during vegetation period 401 mm). The experiment had two crop rotations - biological and cereal. Six treatments of different fertilization intensity were used in both crop rotations: M - farmyard manuring (40 t/ha, two-times in rotation); PK - mineral fertilization using PK-fertilizers; NPK - mineral fertilization using NPK-fertilizes; PK+S+10N - mineral fertilization using PK-fertilizers + straw incorporation + 10 kg nitrogen per ton straw; NPK+S+10N - mineral fertilization using NPK-fertilizers + straw incorporation + 10 kg nitrogen per ton straw; NPK+M - mineral fertilization using NPK-fertilizers + farmyard manure (40 t/ha, two-times in rotation. All the treatments were treated once in 6 years with ground limestone in a dose 3 tone per hectare. From the point of view of grain yields results that the analysed years were greater source of variability of the grain yield than fertilization intensity. The highest grain yields (11.18 t/ha) were reached in the year 1999 and the smallest one (6.14 t/ha, 54.9 %) was reached in the year 1998. Spring barley in biological crop rotation showed the tendency of the better forecrop (8.96) than the winter wheat one in cereals crop rotation (8.68 t/ha, 96.8%). Variability of the grain yield of maize was also affected by fertilization intensity. Weather conditions in the years modified the effect of fertilization and forecrop (significant interaction among years x fertilization and among years x forecrop). The lowest yield was at PK-treatments without nitrogen. The highest yields of maize for grain were obtained using M-treatment, and/or NPK+M. On plot with M was observed tendency of higher yield than on plots PK (not significantly). On plot NPK+M were noted higher yields than on the others variants (PK + straw application, and/or NPK + straw application) with exception farmyard manure. There was significant dependence between grain yield and total precipitation for June and August. Regarding TGW-value and grain weight on spike the effect of forecrop and fertilization was modified by weather conditions. Forecrop and fertilization intensity affected the number of spikes per area. Grain weight on spike was affected by forecrop and by interaction forecrop x fertilization and forecrop x weather. TGW-value was affected by weather, forecrop and by interaction weather x forecrop and weather x fertilisation. Between grain yield and grain weight on spike and TGW-value was found significant dependence. Between TGW-value and total precipitation for June and August was noted significant dependence, too.