In this chapter, the optimum fertilizer requirements of some selected crops and their achievable yields are considered, using 2002 fertilizer and crop prices to compute the value cost ratios (VCRs) of the various crops. The VCR should be higher than 2 to secure a profitable return to the farmer. Under high risk conditions a VCR of about 3 is preferable. The optimum fertilizer requirements in terms of 50 kg bags per ha, the achievable yields with improved technology, the value of this yield at 2002 crop prices and the VCRs are provided in Table 39.
Maize grows best on well-drained sandy loam soils, in areas with a minimum rainfall of 1 016 mm per annum. The rainfall must be well distributed during the growing season. Maize is produced in almost all the agro-ecological zones. Based on the achievable yield, the optimum fertilizer requirements, and the prices of fertilizers and of the crop in 2002, the VCR for maize was 2.7. The major maize producing belt is the
TABLE 39
Optimum fertilizer requirements, maximum crop
yields and VCRs
|
Crop |
Fertilizer type |
Bags/ha |
Fertilizer total cost |
Maximum yield |
Crop value |
VCR |
|
(‘000 Cedis) |
(tonnes/ha) |
(‘000 Cedis) |
Col.6/col.4 |
|||
|
Maize |
AS |
5 |
1 024 |
5.0 |
2 750 |
2.7 |
|
SSP |
5 |
|
|
|
|
|
|
MOP |
1 |
|
|
|
|
|
|
Rice |
AS |
5 |
718 |
6.5 |
7 150 |
10.0 |
|
TSP |
2.5 |
|
|
|
|
|
|
Cassava |
AS |
7.5 |
1 471 |
28 |
7 000 |
4.9 |
|
SSP |
5 |
|
|
|
|
|
|
MOP |
2.5 |
|
|
|
|
|
|
Groundnut |
AS |
1.5 |
661 |
2.0 |
2 400 |
3.6 |
|
SSP |
5 |
|
|
|
|
|
|
MOP |
0.5 |
|
|
|
|
Source: Adapted from MOFA, 2003; SRI (undated).
Transition Zone. This indicates that it is just economic to use fertilizer at optimum rates on maize, especially in the Transition Zone.
Rice is grown in almost in all the agro-ecological zones of Ghana under either flooded or upland conditions. Flooded rice is normally produced on poorly drained Vertisols and Gleysols. In the interior Savannah and Transition Zones, rice is grown on Cambisols and Luvisols. A small percentage of rice is also produced under irrigation. In the Forest Zones rice is also grown under flooded conditions in the valley bottoms where drainage is poor.
In the Northern Savannah and Transition Zones, where extensive ground water Laterites (Plinthosols) occur, rice is produced on imperfectly to poorly drained soils under upland conditions. These soils, which are sandy to silty loam, occur over flat to gently sloping topography and become waterlogged at the peak of the rains.
Under irrigated or flooded conditions, 2½ bags of AS and TSP per hectare are recommended at pre-planting, later top dressed with additional 2½ bags of AS. Under upland conditions 5 bags of AS and 5 bags per hectare of SSP are recommended in split application. Under flooded conditions a VCR of almost 10 can be obtained, suggesting a high profitability associated with fertilizer use.
Cassava is grown in all the agro-ecological zones, with the exception of the Sudan Savannah Zone (Table 36). The suitable soils are the Ferralsols, Luvisols, Acrisols, Nitosols and Cambisols.
The crop thrives best under rainfall of about 1 000 mm per annum, on well-drained, sandy loam soils. The recommended fertilizer requirements of the crop are equivalent to 7½ bags of AS, 5 bags of SSP and 2½ bags of MOP per hectare. Production of the crop with recommended fertilizer application rates gives a VCR of 5, which indicates good profitability.
Groundnut thrives best with rainfall between 760 - 1 300 mm per annum. It requires coarse or fine textured sandy loam soils with good drainage.
The optimum fertilizer requirements, based on the 2002 prices for the fertilizers applied and the crop, are 1½ bags of AS, 5 bags of SSP and ½ bag of MOP per hectare. Based on the 2002 fertilizer and crop prices, a VCR of 3.6 can be obtained (Table 39). Groundnut is a major crop in the Guinea and Sudan Savannah Zones. It is also produced to some extent in the Transition Zone.
