尿素混合生物质炭穴施对土壤氮含量及酶活性的影响

Effects of hole application of urea mixed with biochar on nitrogen content and enzyme activity

为研究尿素与生物质炭混合穴施条件下,生物质炭对土壤氮素转化及土壤酶活性的影响,设单施尿素(N120、N180、N240)、尿素混合生物质炭穴施(N120B、N180B、N240B)处理,施氮量分别为240 kg·hm-2(N240)、180 kg·hm-2(N180)、120 kg·hm-2(N120)和不施氮(CK),生物质炭施用量为10 t·hm-2。测定土壤硝态氮、铵态氮、无机氮和碱解氮的含量,以及土壤脲酶、蔗糖酶和碱性磷酸酶的活性。研究表明,第5 d尿素穴施处理的土壤铵态氮、硝态氮、无机氮和碱解氮含量分别是尿素混合生物质炭穴施处理的4.5~8.2、2.0~3.0、2.55~5.81、3.13~4.46倍,第10 d尿素穴施处理的土壤铵态氮、硝态氮、无机氮和碱解氮含量分别是尿素混合生物质炭穴施处理的24.5~58.9、1.21~1.37、2.99~3.82、1.34~1.48倍,第15 d各处理间土壤氮含量差异不显著。第5 d和第10 d,尿素混合生物质炭穴施处理的土壤脲酶活性均显著高于尿素穴施处理,但在第15 d后处理间无显著差异,第5 d尿素混合生物质炭穴施处理的土壤脲酶、蔗糖酶和碱性磷酸酶活性分别是尿素穴施处理的1.80~2.55、1.07~1.77、1.18~1.22倍,第10 d尿素混合生物质炭N180B处理的土壤蔗糖酶活性最高,N240B处理的土壤碱性磷酸酶活性最高,混合生物质炭处理的蔗糖酶活性是单施尿素处理的2.35~2.37倍。因此,生物质炭促进土壤脲酶、蔗糖酶和碱性磷酸酶活性,吸附土壤中的NH4+和NO3-,赋予土壤氮素缓慢释放特性,尿素混合生物质炭穴施可以促进土壤酶活性,有效降低土壤有效氮素流失的风险。

Biochar is widely recognized as an excellent soil ameliorant as it improves soil properties and protects the soil environment. In this study, potted experiments were conducted to investigate the effects of corn straw biochar on soil enzyme activities and soil nitrogen when urea was mixed with biochar in a hole application. In total, seven treatments were tested, including conventional urea treatment(N120,N180, and N240)and combined hole application of biochar and urea(N120 B, N180 B, and N240 B). The amounts of applied nitrogen were 240,180, and 120 kg·hm^-2 for N240, N180, and N120, respectively, and 10 t·hm^-2 each for the control treatment and urea mixed with biochar in the hole application. Soil nitrogen(nitrate, ammonium nitrogen, inorganic nitrogen, and available nitrogen)and soil enzymes(urease, sucrase,and alkaline phosphatase)were measured. The results demonstrated that the contents of ammonium nitrogen, nitrate nitrogen, inorganic nitrogen, and available nitrogen in soil after a single application of the urea treatments were 4.5~8.2, 2.0~3.0, 2.55~5.81, and 3.13~4.46 times those of the mixed urea and biochar treatment on the 5 th day. The corresponding contents were 24.5~58.9, 1.21~1.37, 2.99~3.82, and1.34~1.48 times those of the urea and mixed biochar treatments on the 10 th day. No significant difference was observed between the soil nitrogen contents of the treatments on the 15 th day. On the 5 th and 10 th days, the activity of urease in the soil subjected to the urea mixed biochar treatment was significantly higher than that in the soil subjected to the urea treatments, but no significant difference was observed between the soil enzyme contents of the treatments on the 15 th day. The activities of urease, sucrase, and alkaline phosphatase in the soil subjected to the mixed urea and biochar treatment were 1.80~2.55, 1.07~1.77, and 1.18~1.22 times of those in the soil that underwent single urea treatments on the 5 th day. The activity of sucrase in the soil with the mixed urea and biochar N180 B treatment was the highest on the 10 th day, while the activity of alkaline phosphatase was the highest for the N240 B treatment, and the activity of sucrase in the soil with the mixed urea and biochar treatments was 2.35~2.37 times of that of the soil subjected to the single urea treatments. Biochar application significantly enhanced the soil urease, sucrase, and alkaline phosphatase activities. Biochar adsorbed NH4^+ and NO3^- from the soil and endowed it with release characteristics, while the hole application of urea mixed with biochar promoted the soil enzyme activities and reduced the risk of effective nitrogen loss from the soil.