CALIBRATION OF SOIL TEST RESULTS FOR PHOSPHORUS AND NITROGEN FERTILIZATION FOR MAIZE (Zea mays L.) PRODUCTION IN NORTHERN GHANA

Abstract

As inherent soil fertility varies for different soils, site-specific fertilization recommendation has long been proposed as more efficient than blanket soil nutrient management. Across northern Ghana, however, blanket recommended rates of nitrogen (N) and phosphorus (P2O5) are used in maize cultivation. Pot and field experiments were conducted from April to December, 2019 to calibrate soil test results and develop nitrogen and phosphorus-predicting tools for site specific fertilization in maize production. Nutrient depleted soils were fertilised with eleven phosphorus rates (00, 05, 10, 15, 20, 25, 30, 35, 40, 45, and 50 kg P2O5/ha) and eleven N rates (0, 15, 30, 45, 60, 75, 90, 105, 120, 135, and 150 kg/ha) in two pot experiments. The N and P levels of the soils before and after nutrient application were analysed to serve as proxi of soil nutrient levels, before planting. The relation between maize growth yield and applied nutrient rate, together with regression analyses of applied rate and corresponding soil test results were used to develop N and P2O5 predicting tools. The developed N and P2O5 predicting tools were evaluated at three sites (Nyankpala, Tamale and Damango) by comparing maize growth and yield of the tool- predicted rates with the optimum performance in the pot experiment. The tools were then validated by comparing performance of tool predicted rate with that of zero fertilization and blanket recommended rates at the three sites in a Randomized Complete Block Design with 3 replications; using the maize var. Wangdataa. The data were subjected to analyses of variance and separated at a probability of 5%. N and P2O5 predicting tools were developed for estimation of site-specific soil N and P fertility, based upon the results of the initial soil chemical analyses. Using the developed tool, the exact N and P2O5 fertilizer rates that are required to achieve optimum maize production could respectively be estimated for a given location. The process involved in the site-specific tool development revealed that for soils that are poor in N and P2O5 nutrients, application of small incremental quantities of nutrients significantly increased growth and yield parameters of maize, including: plant height, leaf area index, hundred seed weight, cob length and weight, straw weight and grain yield. The available P and total N contents of the soils across northern Ghana were below that required for optimum maize growth and development. As such, maize farmers require N and P2O5 fertilization to maximize yield. However, the level of inherent N and P2O5 are not same for all soils, each site therefore requires site specific rate of N and P2O5 application to achieve maximum maize yield. Across all sites, the developed N and P2O5 fertilization tool accurately predicted growth and yield in the range of 90 to 100%. In all cases, there was no significant difference in growth parameters, yield and yield components between the developed tool-predicted rate and that of the blanket recommended rate. However, partial cost analysis due to fertilization indicated that famers can gain 30.5% to 44.6% net saving due to fertilization upon using the developed N and P2O5 predicting tool. Running soil tests could therefore help farmers to know the nutrient status of the soils which could serve as a proxi to estimate site specific fertilization rate and help reduce fertilizer investments by the already resource-constrained farmers. Using the developed calibrated tools would enhance profitability of maize production across the Guinea savannah zone of Ghana.