Evaluation of di-ammonium phosphate(dap) as an alternative basal dressing fertilizer to compound d for maize production on four Zambian soils

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Mulenga, Mwenya K.
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The University of Zambia
Maize is Zambia’s staple food crop, grown by farmers across the country. It is a high nutrient demanding crop that requires adequate amounts of N, P K and other nutrients to obtain economic yields. The recommended basal dressing fertilizer for small scale farmers in Zambia is Compound D, (10: 20: 10) which supplies N, P and K to crops. On soils deficient in N, P, and K it is the ideal fertilizer. Studies have shown that most Zambian soils are deficient in N and P, but not so with K. It is also known that maize yields rarely increase in response to additions of K on soils with high levels of K. The rationale behind using NPK fertilizers on soils with high K can thus be questioned. Fertilizers such as Di-ammonium Phosphate (DAP) (18: 46:0) which only supply N and P, can be alternatives to Compound D on such soils. Greenhouse pot trials and field crop trials were conducted on four P deficient soils to assess the potential of using DAP to replace Compound D for growing maize. The soils comprised a Phaeozem, an Acrisol, and two Lixisols, from Chilanga, Rufunsa, Chongwe and Chibombo districts respectively in Agro-ecological Zone II. Pot trials were conducted in Lusaka, and field trials on-farm, in the mentioned districts. The Phaeozem and Acrisol had high levels of soil organic matter (SOM), while the Lixisols had moderate levels. Furthermore, the Phaeozem, Acrisol and one Lixosol had high levels of K, while one Lixisol had low levels of K. Pot trials were laid out in Completely Randomized Design with 7 rates of DAP of 0, 25, 50, 75, 100, 125 and 150 kg/ha and 200 kg Compound D/ha in triplicate. Maize plants were grown for six weeks. The above ground biomass was harvested, dried and weighed to obtain the dry matter yield. The field trials were laid out in a Completely Randomized Block Design with 8 treatments in quadruplicate. Treatments were the same as those used in the pot trials, with the 25kg DAP/ha treatment replaced by 200 kg DAP/ ha. The maize was grown to maturity, and the grain yield obtained and recorded. Maize dry matter and grain yields from the trials were subjected to Analysis of Variance and comparison of means. The dry matter and grain yields were further used to calculate the Relative Agronomic Effectiveness (RAE) of DAP compared to 200 kg Compound D/ha. Results of the pot trials showed that DAP was as effective as Compound D in producing maize dry matter on the Phaeozem, Acrisol and the Lixisol with high levels of K. On Lixisols with low K, DAP was less effective than Compound D in producing maize dry matter. Results of field crop trials, showed that 100 kg DAP/ha was as effective as 200 kg Compound D/ha on all four soils in producing maize grain yield. The effectiveness of DAP was greater on soils with high K and SOM than on soils with moderate to low SOM. Results of this study have demonstrated that DAP at 100 kg/ha can substitute 200 kg Compound D/ha as a basal dressing fertilizer for producing maize on soils with low P and moderate to high amounts of K and SOM in Zambia. Key words: Maize, Compound D, Di-ammonium phosphate, RAE, phosphorus, potassium, soil organic matter.
soil organic matter--Maize , Farming--Smale scale , Farming--Small scale--Fertilizers