Rotation of Maize with some Leguminous Food Crops for Sustainable Production on the Vertisols of the Accra Plains of Ghana

Five food legumes were grown, as cover/food crops, in rotation with maize, at the University of Ghana, Soil and Irrigation Research Centre, Kpong. The legumes were determinate cowpea (Vigna unguiculata (L.) Walper, var. soronko), indeterminate cowpea (Vigna unguiculata (L.) Walper, var. Adidome mottled), soyabean (Glycine max (L.) Merril, var. GMX 92–16-2M), bambara groundnut (Vigna subterranea (L.) Verd, var. Ada) and groundnut (Arachis hypogea L., var. goronga). The experimental treatments were: incorporated legume residues, recommended inorganic fertilizer application (100 kg N, 60 kg P O and 40 kg K SO ha-1) and no fertilization as 2 5 2 4 control. Soil samples (0-20 cm depth) were analysed for pH, organic carbon (OC) and nitrogen (N) contents before and after the experiments. Samples of the leguminous crops were also analysed for N content. The indeterminate cowpea continued growth after initial setting of pods and, therefore, had greater biomass (total dry weight – TDW) than the other leguminous crops. Its total N was relatively high in spite of lower N content. The TDWs of indeterminate cowpea, soyabean and groundnut were 2.80, 1.90 and 1.85 t ha-1, respectively; the N contents were 2.7, 4.5 and 4.8% and the total N contents were 75.6, 91.2 and 83.3 kg ha-1. Grain yields of maize were higher in the incorporated soyabean and groundnut treatments than the other leguminous crops. In the major rainy season in 2003, grain yield in the groundnut treatment was 3.3 t ha-1, compared with 3.1 and 1.1 t ha-1 in the inorganic fertilizer treatment and the control, respectively. In the minor rainy season in 2004, grain yield was 3.0 t ha-1 in the soyabean treatment, compared with 3.0 and 1.6 t ha-1 in the inorganic fertilizer and control treatments

The Effect of Camber Bed Drainage Landforms on Soil Nutrient Distribution and Grain Yield of Maize on the Vertisols of the Accra Plains of Ghana

The Vertisols of the Accra Plains of Ghana are water logged after significant rainfall due to the low-lying topography (0.1-1 %). Camber bed (Cb) drainage landforms have been developed at the Agricultural Research Centre, Kpong, for draining off excess water. Field experiments were conducted to verify if maize growth and yield gradient from the trough to the crest were the result of nutrient gradient or some other factors. Four 5 m and two 10 m Cbs and a 20-m flatland were prepared in a split-split plot design, with landform as main plot, nutrient levels as sub plot and crop row as sub-sub plot. A pot experiment was also carried out for detailed studies. Soil movement brought about a nutrient gradient from the trough of the camber bed to the crest, and also made the soil profile homogeneous. The trough was low in nutrients, compact and prone to water logging, but nutrient levels increased through the middle slope to the crest. The flatland did not have a nutrient gradient but was prone to water logging due to its low-lying nature. Total dry matter (TDM) of maize and grain yield similarly increased from the trough to the crest. Grain yield of maize on the flatland ranged from 2.5–2.6 t ha- 1, while yields on the 5-m Cb were 3.6, 4.2 and 4.8 t ha-1 on the trough, middle slope and crest, respectively. Excess application of 15-15-15 NPK and sulphate of ammonia fertilizers (150% of recommended levels) did not appreciably increase biomass and grain yield in the troughs. However, the maize crop in pots, with soil from the trough, responded positively to fertilizer application, thus confirming that low yield in the trough was the result of both low nutrient availability and the compact subsoil.

Integrated Organic-Inorganic Fertilizer Management for Rice Production on the Vertisols of the Accra Plains of Ghana

Studies were conducted at the Agricultural Research Centre, Kpong, of the University of Ghana, to find solution to the problem of low rice yields on the Vertisols of the Accra Plains. Rice yields from continuously cropped fields have been observed to decline with time, even with the application of recommended levels of inorganic fertilizers. The decline in yield has been attributed to low inherent soil fertility, which is partly the result of low levels of soil organic matter (OM). As part of the study, cow dung (CD) and poultry manure (PM) were separately applied to the soil at 20 t ha-1 solely and also 5, 10 and 15 t ha-1, in combination with urea fertilizer at 90, 60 and 30 kg N ha-1, respectively. Other treatments included a control and urea fertilizer at 30, 60, 90 and 120 kg N ha-1. There was a basal application of phosphorus and potassium to all plots at 45 kg P2O5 ha-1 and 35 kg K2O ha-1, respectively, based on the recommended fertilizer rate of 90 kg N ha-1, 45 kg P2O5 ha- 1 and 35 kg K2O ha-1, on the Vertisols of the Accra Plains. Studies were also conducted on the redox potential of CD, PM and rice straw (RS). The application of 10 t ha-1 CD and urea fertilizer (at 45 kg N ha-1) and 10 t ha-1 PM and urea (at 60 kg N ha-1) both gave paddy yields of 4.7 t ha-1, which did not differ significantly from the yield of 5.3 t ha-1, obtained under the recommended inorganic nitrogen fertilizer application of 90 kg N ha-1. This indicates a synergistic effect of OM and urea on soil fertility. The redox potential studies showed that RS had greater propensity to bring about reduced soil condition in paddy fields than CD and PM, while PM brought about greater reduction than CD.

Ecological Considerations in the Selection of Leguminous Plants as Cover Crops on The Vertisols of the Accra Plains in Ghana

Experiments were conducted in 2003 and 2004 to select leguminous cover crops for the Accra plains ecology in Ghana, based on the ability to withstand drought, produce enough biomass and fix nitrogen. In a randomised complete block design, Crotalaria ochroleuca, Stylosanthes ha-mata, Stylosanthes guianensis, Aeschenomene histrix, Chamaecrista rotundifolia, Sesbania ses-ban and Leucena leucocephala were grown and plant residues incorporated into the soil. Other treatments were recommended inorganic fertilizer application and no fertilization (control). Maize was planted on all plots and data collected on biomass of leguminous residues and also shoot biomass, cob weight and grain yield of maize. Soil samples were taken and analysed for pH, organic carbon and nitrogen (N). The leguminous plant materials were also analysed for N, phosphorus (P) and potassium (K). Annual rainfalls of 2003 and 2004 were low and dry matter yields of some leguminous plants (e.g. Aeschenomene histrix and Chamaecrista rotundifolia) were consequently low. Also, Crotalaria ochroleuca, Leucena leucocephala, Sesbania sesban and Chamaecrista rotundifolia had higher percentage of N per unit dry weight than the other leguminous plants (3.1, 3.1, 2.8 and 2.8, respectively). In the major rainy season of 2004, maize after Sesbania sesban had higher total dry matter, cob weight and grain yield than observed in the unfertilized control and were comparable to those of the inorganic fertilizer application. Grain yields were 2.4, 0.9 and 3.5 t ha-1, respectively. In the minor season, crop growth and yield were much lower in all the treatments due to low rainfall. By virtue of its high vegetative growth and nitrogen fixation, Sesbania sesban was selected as suitable cover crop for the Accra plains

Utilization of Azolla as manure in lowland rice cultivation on the vertisols of the Accra plains of Ghana

On-farm studies were carried out in order to impart to farmers techniques of using azolla in lowland rice cultivation on the Vertisol. The experiments were conducted on four farms at the Kpong Irrigation Project sites, at Akuse and Asutsuare, from 2002 to 2006. The design of experiment was randomised complete block, with five treatments and four replications. Azolla was grown in designated rice basins (3m x 4 m) for 6 weeks and water drained three days before transplanting rice. Azolla was also grown in external basins and added to give total of 25 t ha-1 fresh weight (1.2 t ha-1 dry weight). As rice was transplanted, azolla was trampled and thus incorporated into the soil. The treatments included: Incorporated azolla only (A1), azolla + 15:15:15 NPK compound fertilizer application (A2), azolla + 15:15:15 NPK fertilizer + ½ sulphate of ammonia fertilizer (A3), application of recommended 15:15:15 NPK fertilizer + sulphate of ammonia (F) and no azolla or inorganic fertilizer application - control (N). Data on the rice crop included: plant height, tillers per plant, total dry weight at booting stage and grain yield at maturity. Soils were sampled at the end of experiments and analysed for pH, nitrogen and organic carbon. The nitrogen content of incorporated azolla was 2.2 %, giving a nitrogen equiva-lent of 27 kg ha-1. Azolla plus 15:15:15 NPK fertilizer gave a yield of 5.3 t ha-1 paddy (A2) that was comparable to that of the recommended inorganic fertilizer applications (F) - 5.1 t ha-1 and greater than the control (N) - 2.9 t ha-1. In Hammond’s farm, where azolla was incorporated over a period of three years, rice yield was higher than observed in Moses’ farm, where azolla incorporation was for one year only. Cost-benefit analysis indicated a 20.7 % savings on fertilizer application