Jesse B. Naab 1 , C. Yamoah 2 , R. Yost 3 and R.A. Kablan 3

1. Comparison of Regional and NuMaSS Fertilizer Rates in On-station and On-farm Trials in Northern Ghana Jesse B. Naab1, C. Yamoah2, R. Yost3 and R.A. Kablan3 1Savanna Agricultural Research Institute, Wa, Ghana 2University of Ethiopia 3Department of Soil Science, University of Hawaii at Manoa, USA

2. Introduction • Low soil fertility, especially N and P deficiency, is a contributing factor to low maize yields in WCA • Application of inorganic fertilizer is obviously one way to overcome soil fertility depletion • Farmers appreciate the value of inorganic fertilizers but only few can afford them because they are costly and risky in the savanna environments where rainfall is uncertain. • In Ghana, the current fertilizer recommendation of 64 kg N, 38 kg P and 38 kg K ha-1 for maize was made in the 1980s irrespective of the initial fertility status of the soil.

3. Introduction…….cont. • Fields vary in fertility and it is therefore important to determine if supplementary fertilizer may be needed. • NuMaSS is a useful tool to determine whether or not supplementary fertilizer is required. • The advantage is NuMaSS can help minimize risk in the savanna environments where rainfall is unpredictable and the cost of fertilizer is usually expensive.

4. OBJECTIVES • To compare the effects of national recommended fertilizer rates with NuMaSS recommended fertilizer rates on maize productivity; • To assess the economic returns of these technologies to farmers

5. Materials and Methods • Field experiments were conducted during 2005 and 2006 growing seasonson-station and on farmers’ fields in the UWR of Ghana • Top soil (0-20 cm) was sampled prior to initiation of the experiments and analyzed for pH, texture, soil carbon, extractable phosphorus (P), and total nitrogen (N). • The analytical results together with field history as well as default values residing in NuMaSS were used as input variables for the model.

6. Table 1:Baseline soil properties on-station and on farmers’ fields

7. Materials and Methods Treatments (On-station & On-farm) • Regional fertilizer rate for maize (reference) • Full NuMaSS rate for continuous maize • Full NuMaSS rate for maize in rotation with groundnut Replications • On-station: 4 • On-farm: 10 fields

8. Table 2: Effect of recommended fertilizer rates on total dry matter of maize as a function of time

9. Table 3: EFFECT OF NATIONAL AND NUMASS FERTILIZER RECOMMENDATIONS ON MAIZE GRAIN YIELD, TOTAL DRY MATTER AND HARVEST INDEX IN 2005 AND 2006

10. Effect of recommended fertilizer rates on grain yield, total dry matter at final harvest and harvest index of maize in on-farm trials

11. Conclusion • From the agronomic point of view, maize yields with NuMaSS recommendations were comparable to the regional recommendation in both experiments.