Nutrient release from rice and rubber biochar tablets with and without embedded fertilizers

An alternative to agricultural residues management is to convert them to biochar because this organic amendment can act as a superior soil conditioner that improves soil productivity. Nevertheless, the low density of biochar poses a challenge in the handling biochar. Tableting of biochar can mitigate the aforementioned problems associated with biochar. The objectives of this study were to determine the physico-chemical properties, nutrient release and soil ammonia volatilization of biochar tablets with and without embedded fertilizers. The different rates of biochar tablets with and without embedded fertilizers impact on selected soil chemical characteristics and nutrient use efficiency (NUE) of sweet corn (test crop) were also determined. Next planting cycle was conducted to determine the effects of combination biochar and fertilizers with and without tableting on selected soil chemical characteristics and NUE of sweet corn (test crop). The composition of biochar mixture was 50% charred rice husk, 30% charred rice straw, and 20% charred rubber twigs. The NPK fertilizers used for this study were ammonium sulfate (AS), triple superphosphate (TSP), and muriate of potash (MOP). The biochar tablet (BT) was produced by blending a biochar mixture with starch followed by tableting using a single punch tablet press whereas the fertilizer embedded biochar tablet (BF) was prepared using the same procedure except that NPK fertilizers were added during blending. Similarly, a combination of biochar and NPK without tableting (Biochar + NPK) was prepared. The ratio of biochar to fertilizers mixture used for the BF and Biochar + NPK production was 2:1. Standard procedures were used to characterize BT, BF, Biochar + NPK, and NPK. The nutrient release of the biochar and fertilizers with- and without- tablets were determined using the water incubation over 30 days. The daily loss ammonia was measured using a closed dynamic air flow system model for 10 days. A pot experiment with six fertilization treatments including control was carried out in an open field located in Perlis, Malaysia to determine the different rates of biochar tablets with- and without embedded fertilizers impact on selected soil chemical characteristics and NUE of the sweet corn (test crop). Sweet corn was cultivated for 53 days (tasselling) and after which the crops were harvested and partitioned into leaves, stems, roots and tassel flowers. The sweet corn plant tissues were analyzed for total C, N, P and K using standard procedures. Soil samples were taken from the pots after the sweet corn plants were harvested and the soil chemical properties were determined. Next planting cycle for the pot experiment with four fertilization treatments including control was conducted to determine effects of the combination biochar and fertilizers with and without tableting on the soil chemical characteristics and NUE of the sweet corn. The procedures used were the same as those used in the previous experiment. Tableting the biochar produced increased the densities of BT (0.70 g cm¯³) and BF (0.90 g cm¯³). Higher density of BF can ease its handling and storage challenges. The blending of NPK fertilizers with the biochar produced, regardless of with and without tableting significantly increased the concentrations of N, P, K, and Ca, which are essential elements required for successful plant growth, development, and reproduction. The presence of NH bend (1614.26 cm¯1) in highly densified BF suggests that the nutrient compounds in BF is more stable against degradation and leaching. The water soluble nutrient release increased in the order of BT < BF < Biochar + NPK < NPK. However, combination of biochar and fertilizers regardless of with and without tableting increased soil ammonia volatilization relative to the NPK fertilizers. The first corn planting cycle demonstrated that co-application of biochar and fertilizers increased soil total C, N, but soil electrical conductivity reduced. Fertilizers only had the lowest effect on the total NUE of the sweet corn. Higher biochar tablet rate and lower rate of fertilizers increased the efficiency of the fertilizers used in the first corn planting cycle. The beneficial effects of tableting the combined use of biochar and NPK on the sweet corn plants’ NUE were more evident in the second planting cycle. The findings suggest that the BF can slowly release embedded nutrients in synchrony with optimum nutrient uptake by the sweet corn. Therefore, transforming fertilizer embedded in biochar into tablet is recommended for sweet corn production following a long-term field study to confirm the findings of this pot study.

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