Effects of different straw biochars on soil organic carbon, nitrogen, available phosphorus, and enzyme activity in paddy soil

Abstract

Biochar is widely used as a soil amendment. Enzyme activity is an important factor that reflects soil metabolic activity, and is involved in biochemical processes such as organic matter decomposition and nutrient cycling in soils. However, the effects of biochar prepared for different straw materials on soil enzyme activity and soil nutrients are rarely studied. Through pot experiments, the effects of different straw (wheat, rice, maize) biochars (obtained by pyrolysis at 500 °C) on soil organic carbon, nitrogen, available phosphorus, and enzyme activity were studied in paddy soil. The results showed that the addition of biochar increased the soil organic carbon content, which gradually decreased with the extension of the rice growth period. The soil ammonium nitrogen content gradually decreased as the rice growth period continued; however, the soil nitrate nitrogen content first decreased and then increased over the rice growth period. Soil invertase, phosphatase, and urease activity first increased and then decreased, and the enzyme activity was the highest at the heading stage of rice. At this time, there were also significant correlations between enzyme activity and carbon, nitrogen, and phosphorus levels, except in the case of soil urease activity. The geometric mean of the investigated enzyme activities was the highest after amendment with rice straw biochar. These results indicate that the response of enzyme activity to biochar depends on the biochar feedstock and the rice growth stage. Biochar has been suggested as a suitable material for soil remediation to improve soil structure, soil moisture retention, soil carbon sequestration and greenhouse gas emissions reductions 1-5. However, the mechanism of soil change due to the addition of biochar are not clear. Some researchers have shown that the response of the soil environment to the addition of biochar depends on the properties of the biochar 6,7. Feedstock and pyrolysis temperatures are key factors influencing biochar performance 7-9. Straw, as an agricultural residue, contains abundant nutrients. Thus, straw incorporation could maintain and potentially improve the contents of soil nutrients. If straw is directly applied to the soil, microorganisms decompose it rapidly and generate gases such as CO 2 , CH 4 , and N 2 O,resulting in nutrient losses. Biochar applications can affect various biogeochemical processes in the soil, including carbon (C), phosphorus (P), and nitrogen (N) cycling 10-12. The addition of biochar can promote the stabilization of soil organic carbon (SOC) 13 , and the ability of soil to maintain N and P 10,14,15. Biochar addition alters the form of N, the subsequent N stabilization and N transformation within the soil 16. Tan et al. demonstrated that when one form of nitrogen was contained within biochar residue another form was released into the soil after biochar addition 12. Biochar-amended soil can affect organic N by converting it into mineral N (ammonium and nitrate) which is directly taken up by the plant. Biochar can serve as...

Effects of Two Types of Straw Biochar on the Mineralization of Soil Organic Carbon in Farmland

“…The higher the amount of biochar applied, the higher the content of organic carbon, which is consistent with the conclusion of [40]. The increase in the organic carbon content may be due to the high organic carbon content in biochar [29]. The CSB treatment increased the organic carbon content more significantly than the BSB treatment.…”

“…The ability of soil to store and supply phosphorus can be reflected by the available phosphorus content, and available phosphorus in soil is also an index of the soil phosphorus level [29]. The results of this experiment showed that the addition of banana straw biochar and cassava straw biochar significantly increased the available phosphorus content and effectively improved the acidity of soil over a long period.…”

“…Total organic carbon (TOC) in the soil was determined by potassium dichromate oxidation spectrophotometry [29]. The pH [30] value was determined by a pH meter at a ratio of soil to water of 1:2.5.…”

“…Soil was extracted by deionized water, and soluble organic carbon (DOC) [31] was determined by a TOC analyzer after centrifugation. Available phosphorus was determined by NaHCO 3 extraction-molybdenum antimony colorimetry [29]. Catalase activity [32] was determined by potassium permanganate titration.…”

Effects of bio-organic fertilizer on soil fertility, microbial community composition, and potato growth

“…It is widely regarded as a promising way for organisms to inhibit soil-borne pathogens and promote plant growth [12,13]. The composition and diversity of the soil microbial community is very important to soil health, and soil enzyme activity is the index of soil biological activ-ity [14,15]. Increasing continuous cropping years results in a decrease in soil nutrients and enzyme activity [16].…”