Effect of Crop Sequencing on Effectiveness of Dorowa Phosphate Rock as a Source of Phosphorus

Abstract

An experiment was conducted in the field to assess the effect of crop sequencing on effectiveness of dorowa phosphate rock (dpr) as a source of p for the following maize crop.. Sugar beans (phaseolus vulgaris), groundnuts (arachis hypogaea), rapeseed (brassica napus), cow peas (vigna unguiculata) and pigeon peas (cajanus cajan) were selected for the study. The crops were combined factorially with five p2o5 levels ; 0, 40, 80 and 120 kg/ha p2o5 to give 25 treatments. The treatments were replicated three times to give 75 plots which were implemented at au and fdt sites. The initial crops were harvested after six weeks and their stover was turned in (except for rapeseed). A maize crop was grown to maturity in the same soils using the residual phosphate. Agronomic records were collected for the initial crop and the maize crop. Significant difference (p<0.05) were observed in mean available p2o5 for the soils to which different initial crops were grown at both sites. Also, significant differences (p<0.001) in available p2o5 at different rates of applied p2o5 at au and fdt were observed. The results from au site showed that 120kg/ha dpr will give available p above 30ppm (mehlich p), which is needed to sustain a good subsequent maize crop according to jones and piha (1989). Rape seed and cowpeas performed best at fdt while pigeon peas and groundnuts performed best at au site. The differences in performance of the initial crops in the two different soils may be related to soil type, initial fertility or rhizosphere activity on phosphate dissolution. Significant interaction between initial crop and applied p2o5 on maize biomass was observed at au site. At fdt the rae of dpr with respect to dsp at 80 kg/ha p2o5 was 80%; 70.6%; 50%; 44%; and 33% for groundnuts, cowpeas, pigeon peas, rapeseed and sugar beans respectively. At au the agronomic efficiency of the dpr combined with the initial crops with reference to dsp at 80kg/ha p2o5 at au was 95%, 143%, 101%, 92% and 88% for cow peas, groundnuts, pigeon peas, and rapeseed and sugar beans respectively. There was a strong correlation observed between soil ph after growth of initial crops and the biomass of the subsequent maize crop at a.u. site. The differences observed in soil available p2o5 and in maize biomass at au did not translate into differences in maize grain yield. Other factors other than available phosphate were concluded to be responsible.