Effect Of Poultry Manure And NPK Fertilizer On The Growth, Yield And Mineral Composition Of Onion (Allium Cepa L.) Grown In Acid Soil

Abstract

Two separate field experiments were conducted at the University of Ghana School farm, Legon, Accra, from 2015 to 2016 to determine the response of “Bawku Red” onion cultivar (Allium cepa L.) to different rates of poultry manure (Pm), NPK fertilizer and combinations of poultry manure and NPK fertilizer. The experimental design used was a randomized complete block design (RCBD) with 10 treatments and 4 replications. The treatments were; T1: Control (no fertilizer), T2: Pm at 5 t/ha, T3: Pm at 10 t/ha, T4: Pm at 15 t/ha, T5: Pm at 20 t/ha, T6: Pm at 5 t/ha + 2.5 t/ha + 2.5 t/ha as side dressing, T7: Pm at 10 t/ha + 2.5 t/ha + 2.5 t/ha as side dressing, T8: Pm at 5 t/ha and NPK 15-15-15 at 300 kg/ha + Urea at 60 kg/ha as a side dressing, T9: Pm at 10 t/ha and NPK 15-15-15 at 300 kg/ha + Urea at 60 kg/ha as side-dressing and T10: NPK 15-15-15 at 600 kg/ha and Urea at 60 kg/ha. The data collected was analysed using the analysis of variance (ANOVA) for randomized complete block design (RCBD) with the help of the GenStat 12th Edition software. Means which differed significantly were compared using the Fisher‟s Protected LSD at 5% level of significance. Associations among some parameters were determined by correlation. The results showed that “Bawku Red” responded positively to the application of soil amendments. Application of 10 t/ha + 2.5 t/ha + 2.5 t/ha of poultry manure on average produced higher vegetative attributes such as plant height (48.9 cm), leaf length (45.4 cm), leaf diameter (10.4 mm), number of leaves (9.5) and fresh shoot biomass (20.8 g/plant) compared to the other treatments at harvest. For bulb yield, application of 10 t/ha + 2.5 t/ha + 2.5 t/ha of poultry manure gave the highest yield of 14.2 t/ha followed by 15 t/ha poultry manure (13.9 t/ha) in experiment one. In the second experiment, poultry manure applied at 15 t/ha gave the highest yield of 15.5 t/ha followed by 10 t/ha + 2.5 t/ha + 2.5 t/ha of poultry manure (14.1 t/ha). Application of 20 t/ha Pm in experiment one and 10 t/ha + 2.5 t/ha + 2.5 t/ha Pm in experiment two increased the soil pH to the highest value of 7.3 and 7.0 respectively compared to the other treatments. The content of some macro nutrients (N, P, K, Ca and Mg) was found to be higher in onion bulbs from the poultry manure and combinations of poultry manure and NPK amendments. The application of NPK 15-15-15 at 600 kg/ha + Urea at 60 kg/ha gave the lowest results among the amended treatments in almost all the parameters evaluated and in some cases, the results were not significantly different form the control (no fertilizer). Total Bulb Yield had a strong significant positive association with Bulb Diameter (0.848**), Bulb Length (0.768**), Leaf Diameter (0.735**), Mean Bulb Weight (1.000**), Number of Leaves (0.652**) and Plant Height (0.728**) in experiment one. In experiment two, the TBY again had a strong significant positive association with BD (0.944**), BL (0.740**), LD (0.656**), MBW (1.000**), NL (0.705**) and PH (0.746**). On average, the application of 5 t/ha of poultry manure produced the highest net revenue (GH¢ 15,435.90) from the two experiments. Generally, the poultry manure and combination of poultry manure and NPK fertilizer amendments improved some of the chemical properties of the soil such as the Total N, available P, Total K, O.C, O.M and pH compared to the control and the NPK fertilizer amendment. It is recommended that farmers adopt 10 t/ha Pm + NPK 15-15-15 at 300 kg/ha + Urea at 60 kg/ha or 5 t/ha Pm + NPK 15-15-15 at 300 kg/ha + Urea at 60 kg/ha amendment, depending on the fertility status of their soil and as much as possible avoid acidic soils in onion production when only chemical fertilizers are used.