Effect of Rising Dose of NPK Fertilizers on Weeds of Grain Sorghum (Sorghum bicolor) on a Calcareous Loamy Chernozem Soil

摘要

The effect of different NPK levels (poor, satisfactory, excessive and toxic) and combinations of these on the soil cover percentage of natural weed flora of grain sorghum (Sorghum bicolor) was studied on a loamy chernozem soil with lime deposit. The Nlevels were 0 (poor), 100 (satisfactory), 200 (excessive) and 300 (toxic) kg ha~(-1) year~(-1); P and K fertilizing was done with 0 (poor), 500 (satisfactory), 1000 (excessive), 1500 (toxic) kg ha~(-1) P_2O_5 and K_2O refilling doses. Later only sustaining of PK levels were targeted, reapplication was repeated every 5-10 years. P and K fertilizer and half of the N fertilizer was spread in autumn before ploughing the plots, the other half of N was spread in spring in the form of 25-28% calcium ammoniumnitrate, 18% superphosphate and 40-60% potassium chloride. The mineral fertilization experiment series was initiated in autumn 1973. Different crops were produced on these plots annually. Grain sorghum was sown in 1992. This long-term experiment series consisted of 4N x 4P x 4K= 64 treatments, or nutritional levels, in two replications, giving a total of 128 plots. The plot size was 6 x 6 = 36 m~2 in mixed factorial design. Weed surveys were done in 4 m2 quadrats in two replications and contained not only weed flora but crop cover, too. The number of weed species, the weed and crop soil cover were highly dependent upon the doses and ratio of different fertilizers.