Organic and Inorganic Soil Amendments Effects on Maize Performance, Economic Returns and Phosphorus Use Efficiency in Kakamega County, Kenya
Psiwa, Rodah Cheptoek
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Low available phosphorus (P) and soil acidity are the key causes of low soil fertility in many cropped soils. A study was conducted two consecutive seasons, 2019 short rains (August - December) and 2020 long rains (March - July) to determine the use of agricultural lime, Minjingu Rock Phosphate (MRP) and compound inorganic fertilizer (NPK) (17:17:17) for optimal maize production and profitability. The experiment was laid out in Randomized Complete Block Design and replicated three times. The objectives were; (i) to evaluate the influence of Lime, MRP and NPK fertilizer on maize growth parameters (ii) to assess the effect of Lime, MRP and NPK fertilizers on crop produce (grain yield) and economic benefits and (iii) to assess the influence of Lime, MRP and NPK treatments on phosphorus uptake and use efficiency. There were six treatments: Lime, MRP, NPK, Lime + MRP, Lime + NPK, and a control. Data on leaf area (LA), leaf area index (LAI), plant height and phosphorus uptake were collected at leaf development (BBCH-19) and tasseling (BBCH-59) whereas yield data were collected at BBCH-89. The plant heights recorded at BBCH-19 were as follows, control (38 cm) < Lime (41 cm) < Lime + NPK (49 cm) Lime + MRP < (60 cm) < NPK (72 cm) < MRP (78 cm). On the other hand, the soil amendments had a significant (p ≤ 0.05) effect on plant height. The highest height (185 cm) at the BBCH-59 stage was recorded in MRP treated plots whereas the lowest values were observed in control (162 cm) and Lime (166 cm) treatments. LA at BBCH-19 was lowest in non-amended control (0.16 cm2) and in Lime treated plots (0.17 cm2) with the highest record (0.42 cm2) being made in plots that received MRP. Plots treated with NPK and Lime + MRP recorded 24 and 31% lower LA, respectively, compared with those amended with MRP. At BBCH-59, the LA differed between treatments and it increased in the order of control (0.48 cm2) < Lime (0.59 cm2) < Lime + NPK (0.64 cm2) < Lime + MRP (0.71 cm2) < NPK (0.83 cm2) < MRP (0.97 cm2). On the other hand, with respect to LAI, Lime + NPK, Lime + MRP and NPK recorded 34, 27 and 14% lower values, respectively compared with MRP. Maize grain yield and economic returns were significantly (p ≤ 0.05) influenced by treatments. Across the seasons, the lowermost yield of 2.2 t ha-1 was obtained from the non-amended plots. The value increased by 4.0, 2.9, 1.8, 1.7 and 0.8 t ha-1 in MRP, NPK, Lime + MRP, Lime + NPK and Lime treatments. The cost of production ranged from US$ 246 in control to US$ 381 in Lime + NPK plots. Nevertheless, use of MRP proved to be the most lucrative with a disposable income of US$ 2122 whereas NPK, Lime + MRP, Lime + NPK, Lime and control recorded 22, 40, 45, 10 and 70% lower values, respectively, compared with MRP. This ensued in greater benefit: cost ratios in MRP (7.6) and NPK (5.9) plots than in control and Lime amended plots that recorded a value of 2.5. At BBCH-19, the average plant P uptake were 3.2, 2.6, 2.0, 1.9, 1.8 and 1.4 kg ha−1 for MRP, NPK, Lime + MRP, Lime + NPK, control and Lime treatments, respectively. Similarly, at BBCH-59, the highest uptake was noted in MRP (7.8 kg ha−1). P use efficiency based on grain yield (PUEY) was such that Lime + NPK (95 kg of maize grain yield for every kg of p supplied) < Lime + MRP (116) < NPK (125) < control (139) < MRP (170) < Lime (188). P use efficiency based on economic returns (PUEE) was lowest in plots treated with Lime + NPK (38 $ kg-1) and Lime + MRP (46 $ kg-1), and highest in Lime (75 $ kg-1) and MRP (68 $ kg-1) plots. When yield was regressed against LA1, strong relationships were noted in Lime + NPK (R2 = 0.60) and Lime (R2 = 0.86) treated plot. The results from the study indicate that the use of MRP amendment could be a promising strategy for managing soil acidity for optimizing maize productivity, economic returns and phosphorus efficacy at Bukura and other related soils in Kenya.