摘要
为探讨还田的棉花秸秆腐解动态及不同还田量的棉花秸秆对小麦产量的影响,于2018-2020年冬小麦播种后,将棉花秸秆机械粉碎覆盖还田,设置全量还田(all stalk returning,AS)、半量还田(half stalk returning,HS)(移出一半秸秆后机械粉碎)、不还田(zero stalk returning,ZS)(移出全部秸秆)3个处理,分析不同还田量棉花秸秆的腐解、养分释放及其结构组分变化规律。结果显示,秸秆腐解速率表现为先快后慢,还田后20 d腐解最快,此后腐解速率逐渐下降;还田后170 d,2018-2019年半量还田和全量还田秸秆腐解率分别为73.4%和66.8%,2019-2020年分别为77.6%和60.4%。秸秆中不同结构组分的释放率存在差异,经过170 d腐解,棉花秸秆可溶性糖释放率为70.7%~81.38%,纤维素腐解率为57.3%~60.7%,木质素腐解率为44.1%~50.3%;秸秆N、P、K释放率也存在差异,N、P、K释放率分别为66.5%~74.7%、71.4%~80.5%和83.1%~87.9%。本研究结果表明,棉花秸秆还田增加了小麦有效穗数,进而提高小麦产量。可见,棉花秸秆还田有利于改善土壤养分状况,提高冬季作物(小麦)产量,其中以全量秸秆还田更好。
我国棉花总产量位居世界第一,如何充分、合理地利用棉花秸秆成为亟待解决的难题。秸秆还田作为当前秸秆利用最重要、最广泛的技术途径之一,秸秆中N、P、K等多种营养物质释放到土壤中,可以补偿作物对土壤养分的消耗,减少肥料投入,防止因焚烧造成的空气污
农作物秸秆的化学组成主要包括纤维素、半纤维素、木质素、可溶性糖等富碳物质以及丰富的N、P、K等营养元
秸秆在土壤中的腐解大致分为3个阶段,秸秆还田后易矿化组分率先被白霉菌和无芽孢细菌分解利用,之后相对易分解的纤维素类物质被纤维素分解菌和芽孢细菌分解,最后某些真菌和放线菌缓慢分解利用木质素、单宁等难分解组
前人研究结果表明,秸秆还田可以提高土壤有机碳和微生物量碳含量、培肥地
试验于2018年11月至2020年6月在华中农业大学试验农场进行。供试土壤为黄棕壤,耕层(0~20 cm)土壤含碱解氮52.4 mg/kg、速效磷33.6 mg/kg、速效钾144.7 mg/kg。条播种植冬小麦后,棉花秸秆(机械)粉碎覆盖还田。棉花品种为华棉3109,小麦品种为郑麦9023,均为湖北省推广应用品种。棉花秸秆还田后,冬小麦生长季(秸秆还田腐解期间)降雨量分别为2018-2019年475.6 mm、2019-2020年463.8 mm(数据来源于本试验田附近100 m内)自动气象站(Campbell Scientific.Inc., USA,包括CR800数据采集器、HMP45C空气温湿度传感器、LI-200X总辐射传感器、TE525MM雨量计传感器、034B风速风向传感器)。
棉花秸秆还田量设置3个水平,0 kg/h
棉花10月底收获后,棉花秸秆(机械)粉粹(不还田处理全部移出、半量还田处理移出一半棉花秸秆),秸秆粉碎长度5~8 cm,均匀覆盖厢面。开沟条播小麦(2018年11月8日播种,2019年5月21日收获;2019年11月18日播种,2020年5月22日收获),小麦田间管理按常规措施进行。
1) 秸秆取样。2018-2019年每20 d 采样1次,2019-2020年于0、20、50、170 d取0.25
2) 秸秆腐解率与腐解速率。棉花秸秆还田t 时间后的腐解率和腐解速率按下式计算:
秸秆腐解率=(M0-Mt)×100%/M0
秸秆腐解速率=(Mt -1-Mt)t/A
式中,Mt为还田后t 时间秸秆质量,g;M0为还田当日的秸秆质量,g;t为连续2次取样的间隔时间,d;A为面积,
3) 秸秆成分。参照文献[
组织成分腐解率=(M0-Mt)×100%/M0
式中,Mt为还田后t 时间秸秆成分含量,g/kg;M0为还田当日的秸秆成分含量,g/kg。
4)秸秆全氮、全磷、全钾测定。称取棉花秸秆样品0.200 g于消煮管,加浓硫酸5 mL摇匀,静置过夜。在消煮炉中消解1~2 h,期间加1~2次高氯酸,每次加5~10滴,消煮后冷却,过滤并定容到100 mL容量瓶中,同时消煮空白对照。待测液稀释5倍后用流动分析仪测定植株N、P含量,用火焰光度法测定棉花秸秆K含量。
养分释放率=(X0-Xt)/ X0×100%
式中,Xt为还田后t时间秸秆N(P、K)含量,g/kg;X0为还田当日的养分含量,g/kg。
由
处理 Treatment | 有效穗数/ Spike number | 穗粒数 Grain number per spike | 千粒重/g 1000-grain weight | 产量 /( kg/ h | ||||
---|---|---|---|---|---|---|---|---|
2018-2019 | 2019-2020 | 2018-2019 | 2019-2020 | 2018-2019 | 2019-2020 | 2018-2019 | 2019-2020 | |
ZS | 218.0c | 205.0c | 25.8b | 30.07a | 46.6a | 41.3a | 2 663.3c | 2 542.4b |
HS | 236.0b | 265.0b | 19.6c | 24.19b | 48.5a | 42.3a | 2 741.8b | 2 710.2b |
AS | 247.0a | 374.3a | 34.7a | 25.08b | 25.08b | 44.6a | 3 962.4a | 4 062.9a |
注: ZS:秸秆不还田;HS:半量还田,1 300 kg/h
不同还田量棉花秸秆腐解率差异显著(

图1 还田量对棉花秸秆腐解率的影响
Fig. 1 Cotton stalk decomposition rates as affected by different returning stalk amounts
棉花秸秆腐解速率整体呈“快-慢-快”的变化趋势,腐解前期还田量少的处理腐解速率快,后期还田量大的处理腐解速率高(

图2 还田量对棉花秸秆腐解速率的影响
Fig. 2 Cotton stalk decomposition rates under different returning stalk amounts
棉花秸秆半量还田比全量还田达到一定累计腐解率所需时间短,2018-2019年半量还田和全量还田处理达到30%、50%、80%的累计腐解率所需时间分别相差42 、35、23 d。累计腐解率从30%到50%和从50%到80%,半量还田分别需要64 d和96 d,全量还田需要57 d和84 d。
不同还田量棉花秸秆纤维素、木质素腐解及可溶性糖释放规律相似(

图 3 还田量对棉花秸秆可溶性糖的释放率(A)和纤维素(B)、木质素(C)腐解率的影响
Fig.3 Soluble sugar(A), cellulose(B), lignin(C) release rates under different returning straw amounts
半量还田处理中棉花秸秆纤维素和木质素比全量还田达到一定腐解比例所需时间短,而还田量对棉花秸秆可溶性糖达到一定的释放比例所需时间无显著影响(
秸秆成分Composition of straw | 处理Treatment | 回归方程 Regression equation | R² | 达到腐解率所需时间/d Time for decomposition | ||
---|---|---|---|---|---|---|
30% | 50% | 80% | ||||
纤维素 Cellulose | HS | y = 0.2485x + 13.688 | 0.978 1 | 66 | 146 | 267 |
AS | y = 0.2688x + 8.3929 | 0.957 5 | 87 | 167 | 288 | |
木质素 Lignin | HS |
y = 5.7962 | 0.983 4 | 48 | 158 | 476 |
AS |
y = 2.7297 | 0.985 1 | 81 | 207 | 490 | |
可溶性糖Soluble sugar | HS | y = 0.3082x + 14.522 | 0.990 6 | 5 | 69 | 166 |
AS | y = 0.3618x + 3.48 | 0.987 5 | 9 | 70 | 162 |
注: x是还田时间,d;y是腐解率,%。Note:x is time after stalk return,d;and the y is decomposition rate ,%.
还田量显著影响棉花秸秆全氮释放率,还田量少的释放率高,但对全磷和全钾释放率无显著影响(

图4 不同还田量棉花秸秆全氮(A)、全磷(B)、全钾(C)释放率的变化特征
Fig.4 Cotton straw total N(A), total P(B), total K(C) release rate under different returning straw amounts
还田后90 d为棉花秸秆全磷主要释放期,半量还田和全量还田处理中全磷的释放率分别为58.8%、55.3%,占磷最终释放率的75.9%、77.4%。110~170 d期间,不同还田量棉花秸秆全磷释放减缓,还田170 d后,半量还田和全量还田处理棉花秸秆磷释放率分别为77.5%和71.4%。2019-2020年,半量还田和全量还田处理在还田后50 d的磷释放率分别占最终释放率的51.1%、50.9%,170 d后,全磷释放率分别达到80.5%和74.3%。
还田后70 d为棉花秸秆全钾主要释放期,半量还田和全量还田处理中全钾的释放率分别为68.4%、63.9%,可占钾最终释放率的77.8%、73.9%。90~170 d期间,不同还田量棉花秸秆全钾释放减缓,还田170 d后,半量还田和全量还田处理棉花秸秆钾释放率分别为87.9%和86.5%。2019-2020年,半量还田和全量还田处理在还田后50 d的钾释放率分别占最终释放率的67.0%、61.5%,170 d后,全钾释放率分别达到83.9%和83.1%。相较于第1年还田,第2年不同还田处理棉花秸秆钾释放率分别下降4.0、3.4百分点。
农作物秸秆在土壤中的腐解受土壤环境、秸秆内在特性和气候条件等多重因素共同影响。本试验中,棉花秸秆干物质衰减呈现先快后慢的2个不同腐解阶段。腐解前20 d的腐解速率最快,前70 d的腐解率占总腐解率的50%以上,此后各处理棉花秸秆腐解速率迅速下降,这是因为腐解前期棉花秸秆易分解物质充足,为微生物活动提供了丰富的碳源,中后期木质素等难分解物质比例升高,微生物活性降低,分解速率变
从棉花秸秆化学组成上看,还田后秸秆中可溶性糖可在短时间内迅速大量释放,且在170 d还田期内可释放80%以上,而纤维素、半纤维素、木质素等结构性物质腐解缓慢且释放率相对较低,表现为可溶性糖>纤维素>木质素,这与前人研究结果一
秸秆N、P、K均表现为直接释放,还田70 d释放量可占最终释放量的50%以上,呈“快-慢”释放规律,平均腐解速率表现为K>P>N,这与前人研究结果一
秸秆还田对小麦有一定的增产效
综上,棉花秸秆还田后170 d(小麦生长季)内,生物质腐解66.8%~73.4%,可溶性糖可释放80%,纤维素腐解60%,而木质素腐解仅为44.1%~51.1%。还田量对纤维素、木质素和可溶性糖的释放速度均无显著影响,棉花秸秆中K释放率最高,可为土壤提供更多的K元素,故秸秆还田后可适当减少钾肥施用量。
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