The effect of the combined application of agricultural waste- and manure-based biochar on soil properties, microbial abundance, CO2 emissions and grass growth

Livestock manure is usually used as an organic fertilizer, yet its direct application to soil can cause several environmental problems, including greenhouse gas (GHG) emissions, N2O emissions and nutrient runoff into ecosystems. Transforming animal manure (AM) into biochar may mitigate these problems. This study evaluated the effects of combining AM biochar and agricultural waste (AW) biochar made from rice husk on soil and forage properties under potted conditions (85 x 32 x 24.2 cm(3) pot). Five biochar treatments (100AW, 75AW25AM, 50AW50AM, 25AW75AM and 100AM, as volumetric ratio) were applied in four replicates. Chemical fertilizers-ammonium sulfate, potassium sulfate and superphosphate-were used as the nitrogen, potassium and phosphorus sources at rates 1.0, 0.5 and 0.5 kg/are, respectively. Soil samples were collected at 10 cm depth for physicochemical analyses, such as bulk density, total pores space, soil pH, water content, cation exchange capacity (CEC), available phosphorus (P), total carbon (TC), total nitrogen (TN) and soil microbial abundance. These analyses were conducted in the greenhouse at 60-, 130-, and 190 days post-biochar application. Due to the suboptimal growth under greenhouse conditions, the grass was reseeded upon transferring the pots outdoors, resulting in successful growth. Carbon dioxide (CO2) emissions were measured every 10 days for 190 days in the greenhouse and additional 40 days outdoors. Results indicated that 50AW50AM biochar or more AM biochar applications reduced soil bulk density, increased total pore space, improved the water retention and increased the soil TC and TN contents compared to AW biochar alone. High AM biochar application did not affect soil microbial abundance, cumulative CO2 emissions or grass yield. Though grass yield effects were limited, biochar nutrient enrichment may be valuable for enhancing soil and plant productivity.