The Effect of Compost Type, Application Rate, and Maturity on Nutrient Leaching and Soil Nutrient Levels

The application of compost to agricultural soils can increase nutrient leaching, causing several environmental problems. Conversely, proper management of compost application can reduce environmental risks. Agronomical trials were conducted in greenhouses in Morocco to compare the effects of varying compost application rates, types, and maturity, as well as the number of growing days, on nutrient availability and nitrate leaching in a loamy sandy soil. Additionally, the study examined the impacts of these factors on soil physical and chemical characteristics. The compost used in this study was derived from a combination of two cost-effective materials, municipal waste, and poultry manure. Tomato plants were cultivated in pots amended with compost over a period of 65 days. The soils were treated with eight composts (plus a control) obtained from municipal solid waste (MSW) mixed with poultry manure (PM) at two ratios, 3:2 and 2:3 weight weight-1 (ww-1) (C1 and C2, respectively), used at two different ages (105 days and 173 days) and at two doses (32.5 g pot-1 and 65 g pot-1, equivalent to 40 Mg ha-1 and 80 Mg ha-1). Two simulated leaching events (the first after planting and the second at harvest) were performed. The concentration of chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) in leachate varied with the number of growing days and increased in the leachate of the non-amended soil after planting. At both sampling times, compost C1, aged 173 days (d), significantly decreased COD in the leachate compared to compost C1 aged 105 d. Compost increased nitrate leaching compared with the non-amended soil. Nitrogen leaching was primarily in the form of nitrate, ranging from 61% to 78% over the whole experimental period. Compost also decreased leachate concentrations of iron (Fe) and chromium (Cr), for other metals, such as cobalt (Co) and nickel (Ni), values were very low. Moreover, compost increased total organic carbon by up to twofold at both sampling times, with the most substantial increase observed with a dose of 65 g pot-1 of compost C2 (aged 105 days). Most compost treatments also increased available phosphorus (P), inorganic nitrogen (N), total nitrogen (TNK), cation exchange capacity (CEC), and electrical conductivity (EC) at both sampling times but had no effect on pH. The metal content in the soil exhibited a decrease compared to the control soil. Overall, our study suggests that nitrogen leaching can be reduced by optimizing compost rates, properties, and stability to synchronize with crop needs.