Enhancement of cattle manure quality and utilisation for crop production on smallholder systems in central Uganda.
There is widespread soil productivity decline in Sub- Saharan Africa attributed to low nutrient stocks and negative nutrient balances. In Uganda in particular, this is due to continuous cultivation and crop harvest without due attention to fertility management. Other causes include uncontrolled soil erosion, unregulated burning of bushes and crop residues. Cattle manure, among other inputs, would be vital in replenishing and recapitalising nutrient stocks in the soils of the region. However, there are limitations for effective and efficient use of this resource including high labour requirements for its preparation and handling, low nutrient content and inadequate knowledge/skills for appropriate handling and management. A study was therefore conducted on smallholder intensive(IS) and semi-intensive (SEI) cattle management systems in Central Uganda to: (i) establish seasonal changes in quantity and quality of available cattle manure; (ii) enhance cattle manure nutrient quality conservation; (iii) rationalise integrated cattle manure and inorganic nutrient sources for crop production; and (iv) evaluate the economic suitability of integrated use of cattle manure and inorganic fertiliser sources for crop production. Informal surveys, on-farm trials and participatory evaluation of economic suitability for integration of cattle manure and inorganic fertilisers with selected farmers were employed to achieve the study objectives. Informal surveys with 8 farmers selected purposively provided opportunity for characterisation of cattle manure and determination of seasonal changes in quality and quantity under IS and SEI. Seasonal changes occurred in cattle manure quality and quantity under both smallholder cattle management systems in Central Uganda. The wet season was superior to the dry season in terms of cattle manure quality irrespective of cattle management system. The cattle manure quality during the wet season was nearly two times greater than during the dry season in respect of various quality parameters including total organic carbon (OC), nitrogen (N), phosphorus (P) and potassium (K). The IS generated manure with higher quality than the SEI irrespective of the season. Under the IS, total OC, N, P and K were nearly twice that of the corresponding quantities in cattle manure under SEI. The available cattle manure per tropical livestock unit (TLU) per household per year under IS is nearly three times more that under SEI system irrespective of the season. Farmers preferred the improved cattle manure management practices to the farmers’ practices against all selected parameters including labour and materials required and retention period. The improved manure management practices were superior to farmers’ practices in terms of cattle manure quality. The total OC, N, P and K under the improved management practices was twice the respective quality of manure under farmers’ management practices, irrespective of management system. Furthermore, total OC, N and P decreased significantly (p<0.05) after 4 weeks of retention by 26 and 55, 65 and 58, 51 and 57% in cattle manure from IS and SEI, respectively. On farm trials were conducted at the 8 farms to rationalise integrated cattle manure and inorganic nutrient sources for crop productivity under IS and SEI. The control (no fertilizer) generated the lowest maize stover, cob and grain yields i.e. 7.0 & 6.6 t ha-1; 8.4 & 7.4 t ha-1 and 5.2 & 5.95 t ha-1 under IS and SEI, respectively. The integration of inorganic P with cattle manure improved its effectiveness for maize yield under both management systems. Maize yield was proportional to increasing levels of manure and inorganic P. Highest stover yields of 15 and 13.9 t ha-1 were generated where manure was applied at 5 t ha-1 and 2.5 t ha-1 plus 20 kg P ha-1 under IS and SEI, respectively. For cob, manure and P applied at rates 2.5 t ha-1 plus 20 kg P ha-1 and 5 t ha-1 plus 20 kg P ha-1 under IS and SEI generated highest yields of 24 and 20 t ha-1, respectively. On the other hand, highest grain yield of 11 t ha-1 was produced where manure and P were applied at rates 5 t ha-1 plus 10 kg P ha-1 and 5 t ha-1 plus 20 kg P ha-1 under IS and SEI, respectively. The tested treatments were assessed through participatory regular observations, recording data on inputs and outputs, presentation and during focus group discussions and scoring involving both farmers and researchers based on agreed indicators. The control generated the lowest net profit under both cattle management systems of UShs 905,000 and 1,055,000 under IS and SEI systems, respectively. However, highest net profits of UShs 1,912,500 and 1,822,500 were generated from 5 t ha-1 of cattle manure plus 10 kg P ha-1 and 5 t ha-1 of cattle manure plus 20 kg P ha-1 under IS and SEI, respectively. These were superior to the control by 52 and 42%, respectively. Despite this, highest marginal benefits were obtained when cattle manure was applied at 2.5 t ha-1 or integrated with 10 kg P ha-1 or 20 kg P ha-1 under the IS and SEI systems, respectively. Marginal ratio for these particular treatments was greater than one, meaning that it is profitable to produce maize at these rates of fertiliser application. Therefore it can be inferred that manure and inorganic P should be applied at rates of 2.5 t ha-1 or integrated with 10 kg P ha-1 or 20 kg P ha-1 under IS and SEI management systems, respectively, for maximum economic benefits from maize production. Nevertheless, farmers preferred manure from improved manure management practices applied at 5 t ha-1 in combination with 10 kg P ha-1 against all selected parameters including grain yields, net profits and cost of maize production.