长期不同养分循环再利用途径对农田土壤养分演替规律与培肥效果的影响研究

Effects of long-term nutrient recycling pathways on soil nutrient dynamics and fertility in farmland

农业生态系统养分循环再利用对土壤养分涵养发挥着重要作用,是培肥地力的有效措施。本研究依托中国科学院栾城农业生态系统试验站始于2001年的农业经营制度长期定位试验,研究长期不同养分循环再利用途径对土壤养分演替规律与土壤固碳效应的影响,为制定地力培育和提升土壤固碳潜能的农业管理措施提供理论依据。选择定位试验的对照处理(CK,不施肥、秸秆不还田)、全部施用化肥(NPK)、化肥+80%地上产出物饲喂猪过腹还田(MNPK)和化肥+全部秸秆粉碎直接还田(SNPK)4个处理作为研究对象,监测土壤有机质、全氮、有效磷含量的动态变化以及土壤碳氮库组成。研究结果表明:实施养分循环再利用显著提高了土壤有机质、全氮和有效磷含量,各养分含量由高到低的顺序均为MNPK>SNPK>NPK>CK。经历18年的不同施肥措施后,与对照相比,MNPK处理0~20 cm土壤有机碳、全氮和有效磷储量分别增加9.21 t(C)∙hm^(−2)、1.01 t(N)∙hm^(−2)和144.87 t(P)∙hm^(−2),SNPK则分别增加4.51 t(C)∙hm^(−2)、0.56 t(N)∙hm^(−2)和24.68 t(P)∙hm^(−2),而NPK的变化依次为0.64 t(C)∙hm^(−2)、0.16 t(N)∙hm^(−2)和29.00 t(P)∙hm^(−2)。这表明秸秆过腹还田的培肥效果显著高于直接还田;秸秆直接还田对碳氮库扩容效果显著,但在秸秆直接还田的有效磷库建设效果甚微。本研究的施肥水平下,若仅施用化肥,则只能维系土壤有机碳氮库基本平衡,对磷库扩容效果显著。从各施肥方式对土壤有机碳组分的影响来看,MNPK和SNPK较NPK显著增加了土壤易氧化有机碳(LOC)和惰性有机碳(ROC)含量,同时也显著增加了活性有机碳在总有机碳中的占比,使(LOC+DOC)/TOC比值由NPK的9.2%分别增加到19.0%和16.3%。表明施用化肥基础上实施养分的循环再利用不仅促进了稳定性碳库积累,亦扩增了土壤活性碳库,对提高土壤的保肥和供肥能力起到了积极作用。从各施肥方式对土壤氮库组分的影响来看,MNPK较SNPK显著增加了硝态氮和铵态氮含量,提高了土壤供氮能力;而SNPK则显著提高了氨基糖态氮含量,表明秸秆直接还田较过腹还田更有利于微生物将速效性氮素固持到过渡库中,不仅降低了活性氮素向环境的输出风险,还提高了土壤对氮素的蓄供能力。鉴于养分过腹还田和秸秆直接还田的培肥效果存在互补作用,建议农业生产中推行秸秆还田基础上提倡有机粪肥替代部分化肥。

Nutrient recycling plays an important role in soil nutrient conservation and is an effective measure for fertilizing soils in agro-ecosystems.This study relied on a long-term experiment(since 2001)on an agricultural management system conducted by the Luancheng Agroecosystem Experimental Station of the Chinese Academy of Sciences.The aim of this study was to provide a theoretical basis for developing agricultural management measures for soil fertility cultivation and enhancing soil carbon sequestration potential.Four treatments were set:no fertilization(i.e.,conventional,CK),all applications of chemical fertilizer(NPK),chemical fertilizer and 80%of the above-ground output feeding pigs through belly(as pig manure)to the field(MNPK),and chemical fertilizer and straw crushed direct return to the field(SNPK).The soil organic matter(SOM),total nitrogen(TN),available phosphorus content(AP),and composition of soil carbon and nitrogen pools of the treatments were determined.The results showed that the implementation of nutrient recycling significantly increased the contents of SOM,TN,and AP in the soil in the order of MNPK>SNPK>NPK>CK.After 18 years,we found that SOC,TN,and AP storage in the 0–20 cm soil layer increased in MNPK by 9.21 t(C)∙hm^(−2),1.01 t(N)∙hm^(−2),and 144.87 t(P)∙hm^(−2),respectively.The SOC,TN,and AP storage in SNPK increased by 4.51 t(C)∙hm^(−2),0.56 t(N)∙hm^(−2),and 24.68 t(P)∙hm^(−2),respectively.The SOC,TN,and AP storage in NPK increased by 0.64 t(C)∙hm^(−2),0.16 t(N)∙hm^(−2),and 29.00 t(P)∙hm^(−2),respectively.This shows that the fertilizing effect of pig manure was significantly higher than that of direct straw return;and the effect of direct straw return on the expansion of carbon and nitrogen pools was significant,but direct straw return had a minor effect on the construction of an effective phosphorus pool.Under the fertilization level of this study,the application of chemical fertilizer alone can maintain the basic balance of soil organic carbon and nitrogen pool,and have a significant effect on phosphorus pool expansion.Compared to NPK,MNPK and SNPK significantly increased the contents of soil labile organic carbon(LOC)and resistant organic carbon(ROC),and significantly increased the proportion of active organic carbon in total organic carbon;thus,the ratio of LOC+DOC to TOC increased from 9.2%of NPK to 19.0%(MNPK)and 16.3%(SNPK),respectively.The results showed that the recycling of nutrients based on the application of chemical fertilizer not only promoted the accumulation of a stable carbon pool but also expanded the soil active carbon pool,which played a positive role in improving the fertilizer conservation and supply capacity of soil.Based on the effects of different fertilization methods on the composition of the soil nitrogen pool,the contents of soil nitrate,ammonium,and total nitrogen supply capacity in the MNPK treatment was higher than those in the SNPK treatment,whereas the SNPK treatment had a significantly higher amino-sugar-nitrogen content than MNPK.This indicates that straw return was more favorable for microorganisms to fix available nitrogen into the transition pool than belly return.Not only does it reduce the export risk of active nitrogen to the environment but also improves the storage and supply capacity of soil to nitrogen.In view of the complementary effect of nutrients returning to the field and straw returning directly to the field,it is suggested that organic manure should be promoted to replace part of the chemical fertilizer based on straw returning in agricultural production.