化学氮肥配施有机肥减缓红壤酸化的机制研究

Overuse of chemical nitrogen (N) fertilizer has accelerated red soil acidification in the last 30 years. The major mechanisms are the release of H+ from nitrification process and nitrate (NO3-) leaching accompanied by cations. Based on a long-term field experiment, we have found that application of chemical N in combination with organic fertilizer could alleviate red soil acidification, but the mechanisms are unknown. The objective of this project is to reveal the mechanisms for combination of chemical N with organic fertilizer to prevent red soil from acidification. The effects of 23- and 27-year fertilization treatments (control, chemical fertilization, organic fertilization, and combination of chemical and organic fertilization) on the fate of N (removal by the shoots of wheat and corn, loss of gaseous NH3-N and N2O-N, NO3-N leaching loss, and changes of soil residual N), and soil acidification indicators (soil pH, aluminum species, exchangeable cations, and soil pH buffering capacity) as well as their relationship will be examined in soils from a wheat-corn experiment located at the Red Soil Research Station, Chinese Academy of Agricultural Sciences in Qiyang, Hunan Province and a corn-corn experiment located at Jiangxi Institute of Red Soil in Jinxian, Jiangxi Province. Laboratory incubation experiments will also be conducted to determine the effects of treatments with different ratios of organic to chemical N fertilizer and composition (C/N ratio, salt of organic acid) of fertilizers on soil N transformation, nitrification potential and rate, and soil acidity. The data will illustrate the mechanisms for soil acidification and advance our understanding of the basic process due to agricultural activities in soil chemistry. The information will be valuable for development of the best fertilization management in southern China in the effort to prevent red soil acidification and preserve soil quality for continuing agricultural production.

近30 年来不合理施用化学氮肥是加剧我国红壤区农田土壤酸化的主要原因， 硝化作用释放H+和硝酸根的淋溶损失伴随盐基离子损失是化学氮肥引起土壤酸化的主要机制。本项目针对长期化学氮肥配施有机肥能减缓红壤酸化但其机制尚不明确这一科学问题，以典型红壤区2个农田长期肥料定位试验为基础，研究长期不同施肥（不施肥、施化肥、施有机肥、化肥与有机肥配施）下肥料氮的去向（作物带走、气体损失、淋溶损失和土壤残留）和土壤酸度有关性质（土壤pH，铝形态，交换性阳离子含量和土壤酸碱缓冲容量等）的演变特征及相互关系，并结合室内培养试验探讨化学氮肥与有机肥配施比例及其碳氮比对土壤氮转化过程、硝化潜势、硝化速率及土壤酸度的影响，以及有机酸盐在抵消化学氮肥酸化土壤中的作用，阐明化学氮肥配施有机肥减缓红壤酸化的机制。研究结果将丰富和完善土壤酸化过程的基础理论，为我国南方红壤区农田土壤酸化防治的合理施肥技术选择提供科学依据。

近年来，我国南方红壤酸化加剧，严重制约了该地区农业的可持续发展。农田土壤酸化主要归因于过量施用化学氮肥。化学氮肥与有机肥配施可有效减缓红壤酸化，但其机理尚不清楚。本项目以红壤旱地长期定位试验为基础研究了（1）长期不同施肥下氮肥去向和土壤酸度基础性质演变特征及其关系，并结合室内培养试验分析了（2）化学氮肥与有机肥配施比例对土壤氮转化过程和土壤酸度的影响，（3）肥料 C/N 比在减缓红壤酸化中的作用，以及（4）有机酸盐对土壤氮转化过程、 CO2和土壤酸度的影响。其主要结果如下：（1）长期单施化学肥料（N，NP和NPK处理）显著降低了土壤pH，8-12年后达到稳定pH4.2或4.5，交换性酸、铝含量升至6.20-7.11和5.51-6.71 cmol(+) kg-1，交换性钙和镁含量降至0.57和0.12 cmol(+) kg-1以下，酸化速率为3.2–3.9 kmol H+ ha-1 year-1；单施或配施有机肥土壤pH增加了1.1个单位或无变化，交换性酸和铝含量降至0.17-0.27和0-0.11 cmol(+) kg-1，交换性钙和镁含量升至8.26-10.77和2.26-2.60 cmol(+) kg-1；长期施用有机肥促进了作物对氮肥的吸收利用效率，减少氢离子（H+）产生量约8.7–12.6 kmol H+ ha-1 yr-1。培养试验表明：（2）有机肥的灰化碱含量和施用量是影响其改良红壤酸度的两个主要因素，添加玉米秸秆降低土壤硝态氮含量并消耗H+是其提高红壤pH的又一机制；（3）总施氮量不变，配施猪粪或玉米秸秆短期内可显著降低土壤硝化速率和H+产生量，从而减缓pH降低，且当玉米秸秆氮配施比例≥50%时，可有效防治红壤酸化；（4）肥料C/N比≥35时，显著降低土壤硝态氮含量和H+产生量，提高土壤pH；（5）配施有机酸盐，土壤pH与CO2累积释放量/土壤硝态氮含量的比值呈极显著正相关，表明去羧基作用消耗H+抵消了硝化作用释放H+，是防治红壤酸化的又一主要过程。可见，化学氮肥配施有机肥增加了肥料C/N比降低了硝化速率和H+产生量，有机阴离子去羧基作用消耗了H+，中和土壤酸度，从而防治红壤酸化。研究结果丰富和完善了土壤酸化过程的基础理论，为我国南方红壤区农田土壤酸化防治的合理施肥技术选择提供科学依据。