Recycling mineral nutrients to farmland via compost application.

Increased cultivation of farmland has resulted in nutrient deficiency and consequently fertility degradation of soils. This research examined the application of composted wastes in terms of the feasibility and effectiveness of recycling plant essential minerals. Minerals in composts (derived from sewage sludge, livestock excrement, and municipal solid wastes, respectively) and in amended soils were observed. Ca/Mg ratios in amended soils and the effect of compost applications (mineral nutrients and heavy metals) on plant uptake were also studied. Results showed that composts, especially those made from sewage sludge and livestock excrement, were richer in mineral nutrients but also contained more heavy metals than untreated soil. The increase in some elements and plant-growth-essential Ca/Mg ratios were found in amended farmlands, implying that compost applications have made up for the nutrient deficiency and have adjusted chemical conditions of the soil. The soil contamination from heavy metals was noticeable. However, some results showed that the large existence of mineral nutrients and heavy metals in soils has caused no significant increase in the plant uptake of elements. The controlled composting process and farmland uses are believed necessary for reducing the heavy metal accumulation in agricultural plants.