Assessment of maize productivity and soil health indicators following combined application of winery solid waste compost and inorganic fertilizers
Masowa, Manare Maxson
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Grape growing and winemaking process generate enormous amounts of solid waste materials that demand more economical and safe disposal technologies. In this study, co-composting and effective microorganisms (EM) technologies were employed to treat the winery solid waste (WSW), thereafter, the resultant compost was assessed for its physico-chemical properties, phyto-toxicity, nutrient release patterns and agronomic potential. Four WSW compost types produced comprised of EM inoculated or uninoculated compost with an initial heap height (hereinafter pile size) of 1.0 or 1.5 m. Samples of the cured composts were evaluated for physico-chemical properties and germination attributes at different extract concentrations (0, 10, 25, 50 and 100%) using cowpea, maize and tomato seeds. The results demonstrated that EM inoculation exerted a significant effect on compost Bray-2 P content while the interaction of EM inoculation and pile size similarly had significant effects on the ammonium-N content. The produced composts possessed high electrical conductivity values due to high concentrations of soluble salts that could be potentially toxic to crops and soil. The use of 1.0 m pile size promoted extended thermophilic phase during compost production that could ensure better sanitization of the final product. Maize and tomato showed higher degrees of phyto-toxicity at 50% extract concentration and above. The phyto-toxicity effects recorded in maize and tomato may be minimized by using lower application rates. The incubation study was carried-out using a buried-bag procedure to determine the P and K release patterns of inoculated compost with 1.0 m pile size in sandy loam soil under field conditions. Grounded compost was thoroughly mixed in zip-lock bags with 900 g surface soil at rates equivalent to 0, 5, 10, 20 and 40 t ha-1. One bag per treatment was destructively sampled at 0, 7, 21, 42, 63, 84, 105 and 126 days of incubation during which the available P and exchangeable K were analyzed. Net mineralized P ranged from -62 to 86 mg kg-1, while the net mineralized K varied between 41 and 2047 mg kg-1. The high net P and K mineralization suggests that the WSW compost can be used as a P and K source. However, its utilization as soil amendment must be cautious to mitigate the potential risks of unnecessary soil pH increase, nutrient imbalance, toxicity and the antagonistic effects of P and K on other plants nutrients. The study was conducted under tunnel house conditions to determine the optimum application rates and agronomic potentials of the WSW compost. The treatment factors comprised of four WSW compost types, seven compost rates (0, 5, 10, 20, 40, 80 and 100 t ha-1) and two sandy loam soils. The results showed a general increase in stem girth, plant height, number of functional leaves per plant, dry matter yield and relative agronomic effectiveness with increasing compost rate. The microbial inoculation and variation of compost with pile size did not induce significant effects on maize performance and soil chemical properties. In most cases, the higher optimum rates predicted by the quadratic model were associated with dry matter yield that were slightly higher in comparison to the optimum dry matter yield predicted by the linear-plus-plateau model. The 80 t ha-1 rates and above significantly increased the exchangeable soil-Na content by up to 175%, thereby causing harm to maize seedlings. Although the WSW compost has an immense potential for the improvement of maize productivity, its application at rates above 40 t ha-1 is detrimental to both plants and the soil. Field trials were conducted during the 2018 and 2018/19 summer cropping seasons to evaluate the effects of sole and combined application of inorganic N and P fertilizers (INPF) and WSW compost on maize performance and soil chemical properties. Inoculated and uninoculated compost types with pile size of 1.0 m were used. The INPF and each compost type were combined in different ratios (0:0, 75:25, 50:50, 25:75 and 0:100, w/w) in such a way that the total mineral N and P supplies from both sources were equivalent to that supplied by the established optimum rate of WSW compost under the tunnel house conditions. The recommended rates of inorganic fertilizers of 200 kg N ha-1 and 90 kg P ha-1 were mixed and included as a standard control. Treatments were arranged in factorial arrangement fitted in a RCBD with three replicates. The results showed a significant interaction effect of compost type and application rate on plant height and leaf area index during the 2018 season, and on number of leaves and stem girth at tasselling during the 2018/19 season. The grain yields recorded from the 25:75 and 50:50 compost-INPF combinations were 6649 and 6246 kg ha-1 respectively and were significantly higher than 4557 kg ha-1 for the untreated control under the harsh environmental conditions of the 2018/19 season. Compost application alone or combined with INPF increased soil pH and the contents of soil organic C, P, K, Na and Zn.