Poultry and green manures as possible alternatives to chemical fertilizers in the semi-deciduous rain forest zone of Ghana

A series of trials involving poultry and green manures were conducted at two sites in the semi-deciduous rain forest zone of Ghana. The poultry manure trials were on a Ferric Acrisol while the green manure was on a Haplic Acrisol. Eight treatments - 0, 2, 4, 6, 8 tons of poultry manure per hectare, 60-40-40 kg NPK/ha, 2 x 2 t/ha and 2 t poultry manure + 30-20-20 kg NPK/ha — were studied in randomised complete block design (RCBD) with five replications in the poultry manure trial. The type of manure used was decomposed dry manure (11.4% moisture content) from layer birds in a deep litter system and point applied in holes. Six treatments - 0, 60-40-40 kg NPK/ha, Green Manure incorporated, Green Manure incorporated + 30-20-20 kg NPK/ha, Green Manure non-incorporated and Green Manure non-incorporated + 30- 20-20 kg NPK/ha — were also used in RCBD with four replications in the green manure trial. Mucuna pruriens (var. Utilis) served as the green manure crop. Both trials used maize (var. Abeleehi) as the test crop. Residual studies using cowpea followed the poultry manure trial. A pot experiment with maize and cowpea in the residual study was also conducted. These trials were aimed at assessing the possibility of using poultry and green manures as suitable alternatives to mineral fertilizers in the semi-deciduous rain forest zone of Ghana. Poultry manure (PM) application registered over 53% increases of N levels in the soil, from 0.09% to 0.14%. Exchangeable cation levels increased with manure application, with K and Ca increasing from 0.02 and 0.95 cmol/kg to 0.09 and above 1.0 cmol/kg respectively. Poultry manure rate of 4 t/ha produced maize grain yield of 2.07 t/ha which was statistically not different from that of the recommended mineral fertilizer rate (2.29 t/ha) and 6 t PM/ha (2.60 t/ha). The 8 t PM/ha rate gave the highest grain yield of 3.08 t/ha and showed the highest residual effect giving significantly higher cowpea grain yield. In the pot experiment however, mineral fertilizer proved to be more efficient in producing the highest maize grain yield. The 8 t PM/ha treatment showed the highest residual effect in the pot. In the green manure trial, soil physical and chemical properties improved with addition of the mucuna green manure. Soil moisture content increased from 9.54 to 10.20 and 11.40% with green manuring while it decreased with chemical fertilizer application. Bulk density decreased with manuring (from 1.42 to 1.36 Mg m-3) while it increased with chemical fertilizer application. The control plot had 0.08% total N while mucuna treated plots had 0. 12% total N. Organic matter levels were 1.29 and 1.37% for mucuna plots and 1.22% for the control. Exchangeable bases increased slightly with mucuna application. The mucuna green manure increased maize grain yields by more than 50% over the chemical fertilizer. A combination of the manures with some amount of chemical fertilizer gave the best yields among all the treatments, emphasizing the importance of an integrated plant nutrient management system. Thus, results of this study indicated that both poultry and green manures were effective in bringing about improvement of soil fertility and maize crop yields and therefore can be good alternatives to mineral fertilizers. The pot experiment lent support to the field experiment that 4 t PM ha1 is to be preferred since it gave consistently optimum yields both in the immediate and residual harvests, especially when economically considered. The 8 t PM ha’ rate may be desirable in the long term. The application of mucuna green manure may not always need to be incorporated to achieve improved soil fertility and maize yields. Further studies are needed to evaluate the long term effects of poultry and green manures as well as their effects on different soil types and other crops.

Source: KNUST