ABSTRACT
The study examined the effects of different rates of nitrogen (N) achieved by various combinations of urea and poultry manure, on growth, yield and efficiencies of nutrient uptake and use of maize. Field experiments laid out in a randomized complete block design with split-plot factorial arrangement were carried out in fertile and N-depleted soils in the early- and late-cropping seasons of 2014 and 2015 in Benin City, situated in the Nigerian rainforest ecology. The main plots consisted of different rates of N achieved by combining poultry and urea (0.00, 20.01, 40.01, 60.01, 80.00, 100.00, and 120.00 kg N ha-1. The sub-plot treatments were maize varieties: Samaz 20 and Samaz 26 (low N-tolerant), TZESR-W and Local Check (high N-requiring).
Application of the different fertilizer combinations (20.01 - 120.00 kg N ha-1) enhanced phenological development, vegetative and ear growth in maize compared to unfertilized maize. Grain yield and components of grain yield markedly reduced in unfertilized maize. Higher chlorophyll content, higher nitrogen uptake efficiency and higher nutrient use efficiency fertilized maize contributed to a higher assimilate production for enhanced performance. In both late- and early-cropping seasons, N-depleted soils required more N than fertile soils (60.01 – 80.00 versus 20.01 – 40.01 kg N ha-1) to promote good vegetative growth, ear development, grain formation, grain yield and stover yield. Each phenological character of maize occurred earlier in late-cropping seasons except ASI which was prolonged, an indication of stress conditions which adversely reduced ear and grain yields, and harvest index of maize. Whereas the efficiency of nutrient uptake was higher in late-season maize, the efficiency of the use of the nutrients was more pronounced in early-season maize.
The attainment of 50% tasselling, 50% anthesis and 50% silking took more days (6-11days) and wider ASI (0.3-1.5 days) in the high N-requiring TZSER-W and Local Check varieties in both fertile and N-depleted soils in each cropping season. TZESR-W and Local Check had high vegetative growth and low grain yield while Samaz 20 and Samaz 26 had high grain yield. The high grain yield of Samaz 20 and Samaz 26 was due to their high HI. The higher nutrient uptake efficiency of the high N-requiring varieties reflected their greater demand for N in soils but the low N-tolerant varieties used this more efficiently. Significant interactions occurred between fertilizer rate and maize variety for some growth and yield characters, and these were prevalent in N-depleted soils in the late-growing seasons, indicating a more nutrient and moisture stressed environment.
