Response Of Rice To Nitrogen Source And Zinc Fertilization In An Irrigated Ecology In Ghana

Abstract

Nutrient management is important to achieve optimum growth and yield of rice. Nitrogen and zinc deficiencies are widespread in most rice cultivating soils and is very important to address these deficiencies to promote high paddy yield. Nitrogen and zinc fertilizers are used to address these deficiencies in rice growth and yield, and the nitrogen source is very important to achieving yield targets. The source of nitrogen fertilizer may influence its zinc uptake due to its unique chemical changes on the soil. Pot and field experiments were conducted at the University of Ghana Soil and Irrigation Research Centre, Kpong (SIREC) under irrigated conditions to examine the effect of nitrogen sources and zinc application rate on the growth, yield and grain zinc content of rice. For the pot experiment a 2 x 6 factorial experiment was laid out in a completely randomised design, with 3 replicates. Two N sources, area and sulphate of ammonia (SoA) at 120 kgN/ha served as the main plots and Zinc rates at, 0 kg ha-1, 5 kg ha-1, 10 kg ha-1, 15 kg ha-1, 20 kg ha-1, 25 kg ha-1, served as subplots with three replicates. The pots were flooded to represent irrigated conditions. Results from the pot experiment showed that interaction between the rate of zinc application and N source did not influence growth and yield parameters of rice. Secondly SoA was a better N fertilizer source than urea in promoting growth and grain yield. SoA application produced higher number of tillers, productive tillers, above ground biomass and percentage filled grains than urea. The grain yield induced by SoA was 13 % higher than urea. Growth and yield components like above ground biomass, plant height, tiller number at maturity, effective tillers, panicle length,100-grain weight and grain yield did not respond to Zinc application. For the field experiment, it was a randomised complete block design, laid out in a split plot design with 3 replicated. it was made of 4 sources of N as main plot and 4 Zinc rates as subplots. The level of N sources included 100 % N from chemical fertilizer (CF100), 75 % N from chemical fertilizer + 25 % N from Poultry manure (CF75PM25), 50 % N from chemical fertilizer + 50 % N from poultry manure (CF50PM50 ) and a control, No nitrogen application (No). The chemical fertilizer was applied in the form of urea. The levels of zinc were 0 kg Zn/ha.(Zn0), 5 kg Zn/ha (Zn5), 10 kg Zn/ha(Zn10) and 15 kg Zn/ha(Zn15). Results obtained from the pot experiment showed there was a significant interaction between N source and zinc rate for number of tillers/m2 and number of panicles/m2. Besides those two parameters interaction between N source and zinc rate did not show any effect on the other growth parameters, grain yield and zinc content in the rice. The relative contribution of N from urea and PM influenced the growth and yield of rice. The grain yield of CF75 PM25 treatment that replaced 25% of the recommended rate of inorganic fertilizers (urea) with PM was at par with the grain yield of urea 100% (CF100). However, (CF100) urea, performed better than (CF50 PM50), when the urea and PM contributed equal parts of N in a ratio of 50: 50. The CF75 PM25 treatment produced the highest grain yield and was not statistically different from Urea 100% (CF100). The results showed that grain yield and number of productive tillers of rice responded to zinc application. Zinc application at 5 kg Zn /ha recorded the highest grain yield. Zinc fertilizer application did not influence zinc concentration in the grains. Application of 5 kg Zn/ha increased zinc concentration in the straw by 13%. Increasing the rate of application (>5kg Zn/ha) did not result in any further increase in the zinc concentration in the straw.