几种施肥模式对红壤氮素形态转化和pH的影响

【目的】为合理施用氮肥减缓红壤酸化，研究不同施肥措施下红壤酸度与氮矿化的关系。【方法】采用室内恒温培养试验研究不同施氮模式（不施肥（CK），20 mgN?kg-1（25%N），40 mgN?kg-1（50%N），80 mgN?kg-1（100%N，尿素，常规施氮量），160 mgN?kg-1（200%N），100%N加化学磷肥（100%N+P），100%N+P加化学钾肥（100%N+PK），100%N+PK加玉米秸秆（100%N+PKS），70%N+PK配施30%有机氮（70%N+PK+30%M），50%N+PK配施50%有机氮（50%N+PK+50%M），30%N+PK配施70%有机氮（30%N+PK+70%M）和100%有机氮（100%M，猪粪））下红壤中NH4+-N、NO3--N和pH的动态变化，并分析相关关系。【结果】与CK相比，各施肥处理均提高了土壤NO3--N、硝化潜势（Np），且尿素氮施用量越大其增幅越大，随有机氮替代尿素氮比例增加其增幅减小。Np最大的是200%N处理（335.62 mg?kg-1）；其次为100%N（152.48 mg?kg-1）、100%N+P（153.36 mg?kg-1）、100%N+PK（148.17 mg?kg-1）和100%N+PKS（148.62 mg?kg-1）处理；而100%N+PKS处理硝化速率k（0.039 d-1）显著低于100%N、100%N+P和100%N+PK处理（k分别为0.051、0.051和0.054 d-1）。各施肥处理土壤NH4+-N和pH均呈先增加，后逐渐下降趋于稳定的变化趋势。培养结束后，与CK相比，土壤pH随尿素氮施用量的增加而显著降低，200%N处理降幅最大,下降了0.92个pH单位；而有机氮替代尿素氮能缓解红壤pH降低。土壤pH与NH4+-N含量呈极显著正相关，而与NO3--N含量和Np之间存在极显著负相关。【结论】施用尿素氮能促进红壤（pH 5.7）硝化作用，加速土壤pH降低，施氮量是影响红壤酸化的主要原因之一；配施玉米秸秆能降低红壤硝化速率，减小NO3--N累积；有机氮替代尿素氮能降低硝化潜势，从而减小红壤酸化的风险。

Experimental Research on Effects of Different Fertilization on Nitrogen Transformation and pH of Red Soil

【Objective】 In order to prevent red soil acidification by regulating nitrogen fertilization,the changes of several forms of soil nitrogen and soil pH,and the correlations among them were studied under different fertilization.【Method】 Incubation experiments were conducted at the temperature of(30±1)℃.The dynamics of NH4+-N,NO3——N and pH after urea application at different rates or combined with other fertilizers(Control(CK),20 mgN·kg-1(25%N),40 mgN·kg-1(50%N),80 mgN·kg-1(100%N,urea,conventional N application rate),160 mgN·kg-1(200%N),100%N plus chemical phosphorus fertilizer(100%N+P),100%N+P plus chemical potassium fertilizer(100%N+PK),100%N+PK plus maize straw(100%N+PKS),70%N+PK combined with 30% organic N(70%N+PK+30%M),50%N+PK combined with 50% organic N(50%N+PK+50%M),30%N+PK combined with 70% organic N(30%N+PK+70%M) and 100% organic N(100%M,pig manure)) were measured.【Result】 Compared with the control treatment,NO3——N,nitrification potential increased and soil pH decreased in all fertilizer treatments,and difference increased with the urea N application rates and decreased with organic nitrogen application rates.The greatest nitrification potential(335.62 mg·kg-1) was observed in the 200%N treatment and second were 100%N(152.48 mg·kg-1),100%N+P(153.36 mg·kg-1) 100%N+PK(148.17 mg·kg-1) and 100%N+PKS(148.62 mg·kg-1) treatments.However,k in the treatment 100%N+PKS was 0.039 d-1 and significant lower than 100%N,100%N+P and 100%N+PK treatments,0.051,0.051 and 0.054 d-1,respectively.NH4+-N and soil pH reached their maximum values between the 3rd and 7th day of incubation after application of fertilizers or no fertilizer,respectively,decreased thereafter,and tended to be stable.Compared with the control treatment,soil pH decreased with the urea N application rates,and the greatest decrease of 0.92 units of soil pH in the 200%N treatment.Combination of organic nitrogen with urea-N slowed down the reduction in soil pH.Soil pH was positively correlated with NH4+-N,while negatively correlated with NO3——N and nitrification potential.【Conclusion】 Urea application could increase nitrification of red soil(pH5.7) and decrease soil pH,and the nitrogen application rate is one of the main factors accelerating acidification of red soil.Urea-N combined with corn straw could decrease nitrification rate,and partial urea-N substitution by organic fertilizer nitrogen can decrease nitrification potential,so decreasing NO3——N accumulation and minimizing acidification risk of red soil.