Abstract
Low soil fertility is recognized as the major constraint to food production and food security in Ghana. An important practice that restores some level of fertility is long fallow, however this is no longer practiced due to increased pressure on land for other purposes. This has resulted in decline in crop yields in areas (forest-savannah transition zone or Sub-humid Ghana) which are known to be one of the major food baskets for the country. The soils are generally poor and require mineral fertilizer to increase crop productivity. In order to increase food production and crop productivity, the use of mineral fertilizer is required other than the expansion of arable land. The aim of this paper is to assess the influence of Phosphorus and Nitrogen fertilizers on the yield of two maize varieties and nutrient use efficiency in the forest-savannah transition zone of Ghana. Experimental data from two maize varieties (Zea mays L.) grown under four concentrations of nitrogen (N) and three concentrations of phosphorus (P) in the 2008 major and minor seasons at two sites in Ejura, Ghana, were used to assess the influence of P and N on the yield, nutrient uptake and use efficiency in the forest-savannah transition zone of Ghana. Analysis of variance showed a statistically significant effect of N and P on grain yield, total biomass, grain N uptake and apparent N recovery. Increasing N concentration significantly increased grain yield, grain N uptake and total dry matter production irrespective of application of P fertilizer. The application of P fertilizer increased N use efficiency with grain yield ranging from 918 (control) to 4953 kg ha−1 (N4P2) and 824 (control) to 4267 kg ha−1 (N4P2) for Obatanpa and Dorke maize, respectively. The two cultivars were significantly different from each other with higher grain yield produced by Obatanpa than Dorke. The application of inorganic P fertilizer increased the efficient utilization of inorganic N fertilizer by the plants in grain yield and total biomass production. Hence, P nutrition of soils is critical for the efficient use of inorganic N fertilizer in the area. Inorganic fertilizer use in the study area was agronomically efficient, though generally more efficient at the Ejura farm site (Experiment 1 and 3) than the Agricultural College site (Experiment 2 and 4). Owing to the spatial variability in soil nutrients in the study area, site-specific fertilizer testing is needed to increase nutrient use efficiency and crop productivity. To improve the rate of fertilizer adoption and use by farmers, the government should subsidize the cost of fertilizer to make it affordable for farmers to purchase to increase crop productivity.
Highlights
Low soil fertility is recognized as the major constraint to food production and food security in Ghana
The low amount of total soil N was as a result of the low soil organic carbon (SOC), which is due to the lack of applied crop residues to fields
There was a higher harvest index (HI) obtained in Obatanpa (2.4 %) compared to Dorke, but this was only significant at Ejura farm site (Expt. 1 and 3)
Summary
An important practice that restores some level of fertility is long fallow, this is no longer practiced due to increased pressure on land for other purposes. This has resulted in decline in crop yields in areas (forest-savannah transition zone or Sub-humid Ghana) which are known to be one of the major food baskets for the country. Phosphorus, the second most widely limiting nutrient in soil after nitrogen (Balemi and Negisho 2012), is a critical macronutrient for plant growth; and in tropical agroecosystems soil, P deficiency is a major limitation to crop production (Mustonen et al 2012). While N is the most limiting nutrient generally in soil, Delve et al (2009) has shown that deficiency of soil P reduces the efficiency of N use by crops
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