长期施肥对新疆灰漠土土壤微生物群落结构与功能多样性的影响

以20a新疆国家灰漠土土壤肥力与肥料效益长期定位试验为平台,采用常规培养法,结合Biolog技术对可培养微生物、生理菌群数量和碳源利用进行测定分析,研究撂荒(CK0)、耕作不施肥(CK)、不同化肥(N、NK、NP、PK、NPK)、化肥配施低量高量有机肥(NPKM1和NPKM2)和秸秆还田(NPKS)等10种处理土壤微生物特征,揭示长期施肥对土壤微生物群落结构与功能多样性的影响。结果表明:(1)可培养微生物:与CK处理相比,CK0处理显著提高了细菌、放线菌和真菌的数量(P0.05),NPKS处理微生物数量则显著降低(P0.05);不同化肥处理的细菌(除PK处理外)、放线菌(除PK和N处理外)数量也有所增加,增幅在8.14%—135.70%和15.30%—44.78%之间;真菌数量(除NK处理外)则有一定幅度的降低;NPKM1和NPKM2处理,微生物数量最高,细菌分别增加了162.20%和173.75%,放线菌增加了34.39%和39.37%,真菌增加了63.33%和488.33%;(2)生理菌群:与CK0相比,CK处理显著提高了自生固氮菌和亚硝化细菌数量(P0.05),显著降低了氨化细菌和纤维素分解菌数量(P0.05);与CK相比,NPKM1和NPKM2处理显著提高土壤中与氮素转化有关的生理菌群数量(P0.05),不同化肥处理和NPKS处理的影响不相同,NPK处理显著高于其余处理(P0.05);(3)微生物碳源利用:微生物活性表现为NK、NPKM1、NPKM2N、NPK、CKPK、NPKSCK0、NP;CK0处理3个多样性指数以及NPKM1、NPKM2和NK处理Shannon(H)指数最高,其余施肥处理差异不显著;糖类、氨基酸类、羧酸类和胺类是微生物利用的主要碳源。(4)聚类分析表明,除NP处理外,施氮处理土壤有较为相似的碳源利用,细菌和真菌与养分之间有较好的相关性,可培养微生物和生理菌群与微生物碳源利用的相关性较差。因此,长期不同施肥对新疆灰漠土土壤微生物群落结构和功能多样性产生了显著的影响,长期耕作不施肥降低了土壤微生物群落结构和功能多样性,不同化肥配合施用对微生物群落的影响不同,NPK及NPK配施有机肥可提高土壤微生物多样性。     

Potassium release characteristics, potassium balance, and fingermillet (Eleusine coracana G.) yield sustainability in a 27- year long experiment on an Alfisol in the semi-arid tropical India

Aims

In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978–2004) years of cropping fingermillet (Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India.

Methods

Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha^?1 farm yard manure (FYM), 10 Mg ha^?1 FYM +50 % NPK, 10 Mg ha^?1 FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO₃ (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl₂ (mild extracting solution).

Results

Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions.

Conclusion

For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity.     

长期施肥对土壤微生物量及土壤酶活性的影响

 该文以北京国家褐潮土土壤肥力与肥料效益长期监测基地的长期肥料定位试验为平台,研究了长期不同施肥制度对土壤的生物学特性及其土壤酶的影响。主要研究结果：长期撂荒土壤(15年)的有机质和全氮(TN)的含量、微生物量碳(SMB-C)和氮(SMB-N)、土壤的蔗糖酶、磷酸酶和脲酶活性以及SMB-C/SOC(土壤有机碳)和SMB-N/TN比值都高于种植作物的农田土壤;而其代谢商和容重值低于农田土壤。长期施肥的农田(NPK、NPKM 、NPKS和NPKF),其土壤养分含量、微生物量碳和氮以及土壤蔗糖酶、磷酸酶和脲酶活性均高于不施肥的农田(CK);而小麦(Triticum aestivum)-玉米(Zea mays)→小麦-大豆(Glycine max)复种轮作(NPKF)的农田又高于长期复种连作(NPK)的农田;在施肥处理中(NPK、NPKM、NPKS和NPKF),长期化肥与有机肥配合施用的处理(NPKM )的土壤上述指标高于其它施肥处理(NPK、NPKS和NPKF),但其土壤的代谢商、pH值和容重值较低。     

黄泥田土壤真菌群落结构和功能类群组成对施肥的响应

研究长期不同施肥黄泥田土壤真菌群落组成和功能特性,深入认识真菌对不同施肥的响应机理,可以为合理施肥和保证农田土壤健康发展提供科学依据.设置不施肥(CK)、单施无机肥(NPK)、无机肥配施农家肥(NPKM)、无机肥加秸秆还田(NPKS)4个处理,采用Illumina高通量测序和FUNGuild对不同施肥处理下黄泥田土壤真菌群落结构和功能群进行分析.结果表明:从门水平上看,土壤真菌群落主要由子囊菌、担子菌和接合菌构成,且以子囊菌为主(47%~74%).NPKM和NPKS处理中子囊菌的相对丰度分别为49%和47%,显著低于CK(71%)和NPK(74%)处理,从目水平上看,减少的主要为肉座菌、格孢腔菌和散囊菌.NPKM和NPKS处理担子菌相对丰度分别为18%和28%,高于CK(14%)和NPK(10%)处理,从目水平上看,增加的主要为银耳菌、糙孢伏革菌和伞菌.与CK相比,单施无机肥降低了担子菌含量.不同施肥处理均在一定程度上增加了接合菌门的丰度,从目水平看,以内囊霉菌和粪蛙霉菌为主.NPK处理真菌α多样性指数显著低于其他处理,NPKM和NPKS处理的丰富度指数(Chao1和ACE)高于CK和NPK处理.不同处理之间真菌的营养类型以腐生营养型为主(48%~57%),NPKM和NPKS处理的共生营养型真菌相对丰度为17%,显著高于CK和NPK处理,增加的以丛枝菌根真菌、外生菌根真菌为主.NPK处理动物病原菌含量(10%)显著高于其他处理.冗余分析(RDA)结果表明,土壤含水量、孔隙度和盐度是影响真菌群落结构和功能类群组成的主要因子,其次为有机质和总氮.长期单施无机肥降低真菌种群多样性,增加致病菌含量,不利于土壤健康,而有机无机肥配施可在一定程度上提高真菌种群丰富度指数和共生真菌比例,有利于保持黄泥田稻田土壤健康的生态环境和真菌群落的多样性.     

Nitrogen release from incorporated 15N-labelled Chinese milk vetch (Astragalus sinicus L.) residue and its dynamics in a double rice cropping system

Background and aims

Chinese milk vetch (Astragalus sinicus L. CMV), a leguminous cover crop, has been shown to provide N benefits to rice crops, but little is known about the pathway of incorporated CMV and its N dynamics. In this study, effects of CMV under different application treatments (incorporated alone, applied in conjunction with urea fertilizer and applied with ryegrass (Lolium multiflorum Lam.)) on N dynamics, rice yields and N uptake were investigated and compared with those of chemical fertilizer (CF) and no fertilizer (NF) in a double rice cropping system.

Methods

Nitrogen release from incorporated CMV residue was quantified by using a bag method. Nitrogen dynamics of CMV were evaluated by using ¹⁵N-labelled fresh CMV tops and compared with those of CF (¹⁵N-labelled urea).

Results

CMV residue decomposition pattern and its N release pattern followed a single exponential decay model, with 87.8–89.5 % of the applied CMV decomposed and 95.1–96.1 % of the original N released in the double rice season (177 days after fertilizer application). CMV treatments had higher rice N uptake efficiency than CF (39.2–51.3 % vs. 29.9 %) at the sum of early and late rice seasons. Rice yield, N accumulation and mineral fertilizer efficiency in CMV treated treatments were higher than those in CF. After two consecutive rice seasons the amounts of residual N remained in the soil were higher in the CMV treated fields than in CF (29.4–33.2 % vs. 14.1 %).

Conclusions

CMV can be considered an efficient N source alternative to chemical fertilizer in double rice cropping systems.     

长期不同施肥制度下几种土壤微生物学特征变化

 为阐明土壤微生物对土壤健康的生物指示功能, 以国家褐潮土肥力与肥料效益监测基地的长期肥料试验为平台, 应用BIOLOG ECO微平板培养法与常规分析法研究了长期施肥15年后不同施肥制度对土壤微生物生物量、活性、群落代谢功能多样性及土壤肥力的影响。研究结果表明, 与对照(CK)相比, 长期化肥与有机肥配施土壤中土壤有机质(SOM)、全氮(STN)、全磷(STP)含量升高, 土壤C/N与pH值降低, 土壤微生物量碳(Soil microbial biomass carbon, SMBC)、生物微生物量氮(Soil microbial biomass nitrogen, SMBN)、微生物商(qMB)及脲酶(Urease)活性升高, BIOLOG ECO微平板平均颜色变化率(Average well color development, AWCD)、土壤微生物代谢功能多样性指数变化不明显。和长期单施化肥处理(NPK)相比, 长期化肥与有机肥配施处理中上述几种微生物学特征(SMBC、SMBN、qMB、Urease及AWCD、代谢功能多样性指数)均呈极显著增加。NPK处理与CK相比虽然SOM、STN、STP含量稍有升高, 土壤C/N与pH值降低, SMBC、SMBN、qMB及Urease活性增高, 但是AWCD、土壤微生物代谢功能多样性指数却显著下降。过氧化氢酶活性(Catalase)在各处理土壤中的差异不显著。土壤微生物碳源利用的主成分分析表明, 长期不同施肥各处理在土壤微生物利用碳源的种类和能力上有差异。此试验说明, 土壤微生物受农业管理措施和多种环境因素的影响, 土壤微生物学特征可作为土壤质量的敏感指标, 为提高作物产量、增强肥力提供理论参考。     

Comparison of crop productivity and soil microbial activity among different fertilization patterns in red upland and paddy soils

Soil enzyme activity and microorganism community can be changed through different long-term fertilization patterns. However, the effect of different fertilization practices on soil microorganisms might differ among crop systems. The objective of the study was to reveal the change of soil enzyme activity and soil microorganism community in different fertilizations both in upland and paddy soils. Therefore, based on long-term fertilization experiments in upland soil started in 1986 and adjacent paddy soil experiment commenced in 1981, with both consisting of 4 treatments: Control (no fertilization), N (only nitrogen fertilizer), NPK (nitrogen, phosphate and potassium fertilizers) and NPKM (nitrogen, phosphate and potassium fertilizers plus organic manure), grain yield, soil fertility, activities of soil urease, catalase, acid phosphatase, microorganism community (the number of bacteria, fungus and actinomycete) were analyzed. The result showed that: the highest grain yield was attained under the application of chemical fertilizers plus manure, as compared with Control, NPKM significantly increased the grain yield by 908.63% in corn and 118.80% in rice (p < 0.05). Meanwhile, NPKM treatment increased significantly soil organic matter and nutrient contents in upland and paddy soils. Interestingly, there was no significant difference in soil pH among all the treatments of paddy soil, but in upland, NPKM increased pH in comparison to Control by 23.06% (1.15 units of pH). Compared with Control, soil urease, catalase activities, bacteria and actinomycete numbers of NPKM were increased by 321.39%, 129.64%, 229.79%, 85.81% in upland soil, and 25.11%, 251.12%, 292.83%, 196.34% in paddy soil. However, in paddy soil, the soil acid phosphatase activity of Control, NPK and NPKM treatments were higher than upland soil by 34.87%, 44.81%, 52.73% and 30.11%. Then, the soil fungus and actinomycete numbers of paddy soil were lower than upland soil by 20.20% and 88.29%. Therefore, it indicated that long-term application of chemical and organic fertilizers delivered highest productivity in both experiment but the effect of fertilizer practices differed between land uses.     

平衡施肥对缺磷红壤性水稻土的生态效应

为了研究平衡施肥对缺磷水稻土的生态效应,对长期缺施磷肥水稻土进行了3.5年平衡施肥试验。试验采取盆栽水稻的方式,在长期缺施磷肥的红壤性水稻土上比较不施磷肥（NK）、平衡施用氮磷钾无机肥（NPK）、无机氮磷钾肥配施硅肥（NPKSi）、无机氮磷钾肥配施有机肥（无机肥占3/5）、NPK基础上增施磷肥（NKhP）、NPKM基础上增施磷肥（NKhPM）处理的土壤肥力、土壤微生物特性、土壤磷的渗漏量以及地上部水稻产量、养分利用率、磷肥利用率的变化。试验表明,平衡施肥处理NPK、NPKSi、NPKM、NKhPM显著提高水稻产量,比不施磷肥（NK）平均增产147%,其中NPKM提高152%;能提高土壤肥力,比不施磷肥土壤有机质含量平均提高18.5%,其中NPKM提高30.1%;显著提高土壤微生物生物量,比不施磷肥土壤微生物生物量碳（MBC）平均提高57.2%,其中NPKM提高87.1%;提高氮素、钾素养分利用率,比不施磷肥平均分别提高120.3%、33.6%,其中NPKM分别提高152%、43%。而长期重施无机磷肥处理（NKhP）虽然水稻产量比不施磷肥处理提高125.1%,但因土壤中磷酸根离子含量过高影响土壤微生物正常生长,土壤微生物活度比不施磷处理降低9.4%,土壤微生物量碳（MBC）降低2.4%,稻田土壤微生物生态系统质量劣化。此外,重施磷肥处理（包括NKhP、NKhPM）易导致稻田水体的磷污染。各处理比较,NPKM综合生态效应最佳,以下依次是NKhPM、NPKSi、NPK,NKhP,NKhP对稻田土壤微生物生态系统产生负效应。根据试验结果,平衡施肥是恢复缺磷水稻土的有效措施,其中在平衡施用氮磷钾化肥的基础上增施有机肥或硅肥效果较好。     

不同施肥处理对土壤水稳定性团聚体及有机碳分布的影响

以国家褐潮土16 a的长期肥料试验为平台(北京昌平),研究长期不同施肥对耕层土壤水稳定性团聚体及其有机碳的影响。主要研究结果:与耕种农田土壤相比,长期撂荒(CK0)可以提高水稳定性大团聚体的含量及其有机碳含量和储量。而农田耕作后,破坏了水稳性大团聚体,相应地增加水稳性微团聚体的含量。与长期不施肥种植作物(CK)相比,长期施氮磷钾肥(NPK)、氮磷钾配施有机肥(NPKM)和氮磷钾秸秆还田(NPKS)处理对水稳性团聚体数量分布和平均重量直径(MWD)有显著影响,其中对2mm和0.25 2mm水稳性大团聚体的促进作用最明显,说明施肥处理增加的新碳主要向0.25 2mm和2mm团聚体富集。在不同水平水稳性团聚体中,2mm和0.25 2mm两个级别的水稳性大团聚体有机碳的含量显著高于0.0530.25mm和0.053mm水稳性微团聚体。化肥与有机肥配施(NPKM)处理可提高水稳性大团聚体含量,改善土壤团聚体的结构。长期小麦-玉米→小麦-大豆复种轮作并施氮磷钾化肥的处理(NPKF)各级团聚体中有机碳的含量高于长期小麦-玉米轮作并施氮磷钾化肥的处理(NPK)。     

Nitrogen use efficiency of organically fertilized white cabbage and residual effects on subsequent beetroot

Background and aims

The low N availability in organic cropping systems requires an efficient use of the limited N sources. The study aimed to analyze the N efficiency of organically fertilized white cabbage on a crop and crop rotation basis.

Methods

Effects of soil-incorporated lupine seedlings and seed meal on the N use efficiency (NUE) and individual NUE components of cabbage were investigated in field experiments. Cabbage was followed by beetroot to quantify residual fertilizer effects.

Results

Generally, NUE decreased with increasing N availability. Nitrogen uptake efficiency, however, was low at low N supply and increased curvilinearly to an asymptotic maximum. Variation in harvest index between and within experimental years was explained by differences in thermal growing time and initial cabbage growth, respectively. The increase in beetroot N supply by fertilizer treatments averaged 18 % of applied lupine seed N corresponding to 63 % of the incremental N in cabbage residues.

Conclusions

Dry matter partitioning alters during cabbage yield formation in favor of the harvest residue fraction if abiotic stress like water shortage occurs directly after crop establishment, being associated with reduced NUE. The residual effect depends largely on the re-utilization of incremental fertilizer N in cabbage residues and thus on the short-term net N mineralization of organic fertilizers.     

Fertilization regimes affect the soil biological characteristics of a sudangrass and ryegrass rotation system

The sudangrass (Sorghum sudanense) and ryegrass (Lolium multiflorum L.) rotation is an intensive and new cropping system in Central China. Nutrient management practices in this rotation system may influence soil fertility, the important aspects of which are soil biological properties and quality. As sensitive soil biological properties and quality indicators, soil microbial community activity, microbial biomass, enzyme activities, soil organic matter (SOM) and total N resulting from different fertilization regimes in this rotation system were studied through a four-year field experiment from April 2005 to May 2009. Treatments included control (CK), fertilizer phosphorus and potassium (PK), fertilizer nitrogen and potassium (NK), fertilizer nitrogen and phosphorus (NP) and a fertilizer nitrogen, phosphorus and potassium combination (NPK). Soil microbial community activities in the NK, NP and NPK treatments were significantly lower than those in the CK and PK treatments after the sudangrass and ryegrass trial. The highest microbial biomass C, microbial biomass N, SOM, total N, sucrase and urease activities were found in the NPK treatment, and these soil quality indicators were significantly higher in the NK, NP and NPK treatments than in the PK and CK treatments. Soil microbial biomass and enzyme activities were positively associated with SOM in the sudangrass and ryegrass rotation system, indicating that fertilization regimes, especially N application, reduced microbial community activity in the soil. Proper fertilization regimes will increase microbial biomass, enzyme activity and SOM and improve soil fertility.     

The critical soil P levels for crop yield, soil fertility and environmental safety in different soil types

Background and aims

Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China.

Methods

Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl₂-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point.

Results

The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg^?1 to 21.4 mg kg^?1, above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg^?1 to 90.2 mg kg^?1, above which soil CaCl₂-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg^?1 to 71.8 mg kg^?1 among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content.

Conclusions

The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.     

Methane and nitrous oxide emissions from direct-seeded and seedling-transplanted rice paddies in southeast China

Background and aims

The rice production is experiencing a shift from conventionally seedling-transplanted (TPR) to direct-seeded (DSR) cropping systems in Southeast Asia. Besides the difference in rice crop establishment, water regime is typically characterized as water-saving moist irrigation for DSR and flooding-midseason drainage-reflooding and moist irrigation for TPR fields, respectively. A field experiment was conducted to quantify methane (CH₄) and nitrous oxide (N₂O) emissions from the DSR and TPR rice paddies in southeast China.

Methods

Seasonal measurements of CH₄ and N₂O fluxes from the DSR and TPR plots were simultaneously taken by static chamber-GC technique.

Results

Seasonal fluxes of CH₄ averaged 1.58 mg m^?2 h^?1 and 1.02 mg m^?2 h^?1 across treatments in TPR and DSR rice paddies, respectively. Compared with TPR cropping systems, seasonal N₂O emissions from DSR cropping systems were increased by 49 % and 46 % for the plots with or without N application, respectively. The emission factors of N₂O were estimated to be 0.45 % and 0.69 % of N application, with a background emission of 0.65 and 0.95 kg N₂O-N ha^?1 under the TPR and DSR cropping regimes, respectively. Rice biomass and grain yield were significantly greater in the DSR than in the TPR cropping systems. The net global warming potential (GWP) of CH₄ and N₂O emissions were comparable between the two cropping systems, while the greenhouse gas intensity (GHGI) was significantly lower in the DSR than in the TPR cropping systems.

Conclusions

Higher grain yield, comparable GWP, and lower GHGI suggest that the DSR instead of conventional TPR rice cropping regime would weaken the radiative forcing of rice production in terms of per unit of rice grain yield in China, and DSR rice cropping regime could be a promising rice development alternative in mainland China.     

长期不同施肥处理对苹果产量、品质及土壤肥力的影响

通过连续7年(2003-2010年)的田间定位试验,研究了不同施肥处理\[不施肥对照,CK;不施N肥只施PK肥,PK;不施P肥只施NK肥,NK;不施K肥只施NP肥,NP;单施NPK化肥,NPK;单施有机肥(猪粪),M;化肥有机肥配施(化肥有机肥氮各占一半),NPKM\]对渭北旱塬富士苹果产量、品质及果园土壤养分含量变化的影响.结果表明: 施肥可以提高苹果产量,连续7年不同施肥处理苹果平均产量较对照提高14.4%～63.8%,各处理苹果年平均产量顺序为:NPKM＞NPK≥M＞NP≥NK＞PK＞CK.NPKM、M、NPK处理随着试验时间的推移,果实可溶性糖、维生素C、可溶性固形物含量呈上升趋势,NPKM、M处理不同年际间波动相对较小;NPKM处理糖酸比5年较对照提高了30.9%,维生素C含量提高了17.5%.长期合理施肥有利于提高土壤有机质,NPKM、M处理0～20 cm土层有机质含量提高幅度最大,分别提高了28.8%和29.3%. NPK、NPKM、M处理土壤各层速效氮、有效磷、速效钾含量较试验前均有显著提高,NPK处理0～20 cm、20～40 cm和40～60 cm土层速效氮含量分别提高了22.7%、37.3%和53.4%.与NPK处理相比,NPKM处理的土壤速效磷含量提高了18.7%,且不同处理土壤速效磷含量上层显著大于下层.
     

Properties of anthropogenic soils in ancient run-off capturing agricultural terraces in the Central Negev desert (Israel) and related effects of biochar and ash on crop growth

Background and aims

In the Central Negev hills (Israel) many ancient terraced wadis exist, which captured run-off and caused gradual soil aggradation, which enabled agricultural practices. In these terraces, dark colored soil horizons were observed, containing charcoal, as can be found in Terra Preta soils, suggesting higher fertility compared to natural soils. The aim of our investigation was to investigate these anthropogenic soils and to study the effects of charcoal and ash addition on soil properties and crop growth.

Methods

We investigated 12 soil profiles, focusing on possible differences between light and dark colored soil horizons. We also investigated the effects of amendment of charcoal and ash on the growth of wheat (Triticum Aestivum L.) in a 40-day pot experiment involving two water regimes.

Results

Results show that charcoal content in light and dark horizons were both low (<0.2 %), but significantly lower bulk densities were found in dark colored horizons. In the crop experiment, charcoal addition resulted in decreased crop growth, while, in the water deficit regime, ash addition resulted in increased crop growth.

Conclusions

Considering the observed charcoal and the results from the crop experiment, we hypothesize that, in ancient run-off capturing agricultural systems, ash was purposefully added as fertilizer.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil

Aims

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.

Methods

We adopted 4.5 t ha^?1, 9.0 t ha^?1 biochar and 3.75 t ha^?1 straw for each crop season with an identical dose of NPK fertilizers.

Results

We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH₄ emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N₂O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH₃ volatilization in the rice season, but stimulated it in the wheat season.

Conclusions

Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH₄ mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH₃ volatilization differently in the flooded rice and upland wheat seasons, respectively.     

Assessment of nitrate leaching loss on a yield-scaled basis from maize and wheat cropping systems

Background and aims

It is so far a gap in knowledge to assess nitrate (NO₃ ^?) leaching loss linking with crop yield for a given cereal cropping system.

Methods

We conducted a meta-analysis on 32 published studies reporting both NO₃ ^? leaching losses and crop yields in the maize (N?=?20) and wheat (N?=?12) systems.

Results

On average, 22 % and 15 % of applied fertilizer N to wheat and maize systems worldwide are leached in the form of NO₃ ^?, respectively. The average area-scaled NO₃ ^- leaching loss for maize (57.4 kg N ha^?1) was approx. two times higher than for wheat (29.0 kg N ha^?1). While, if scaled to crop yields, the average yield-scaled NO₃ ^? losses were comparable between maize (5.40 kg N Mg^?1) and wheat (5.41 kg N Mg^?1) systems. Across all sites, the lowest yield-scaled NO₃ ^? leaching losses were observed at slightly suboptimal fertilization rates, corresponding to 90 % and 96 % of maximum maize or wheat yields, respectively.

Conclusions

Our findings suggest that small adjustments of agricultural N management practices can effectively reduce yield-scaled NO₃ ^? leaching losses. However, further targeted field experiments are still needed to identify at regional scale best agricultural management practices for reducing yield-scaled NO₃ ^? leaching losses in maize and wheat systems.     

Effects of long‐term straw return on soil organic carbon storage and sequestration rate in North China upland crops: A meta‐analysis

Soil organic carbon (SOC) is essential for soil fertility and climate change mitigation, and carbon can be sequestered in soil through proper soil management, including straw return. However, results of studies of long‐term straw return on SOC are contradictory and increasing SOC stocks in upland soils is challenging. This study of North China upland agricultural fields quantified the effects of several fertilizer and straw return treatments on SOC storage changes and crop yields, considering different cropping duration periods, soil types, and cropping systems to establish the relationships of SOC sequestration rates with initial SOC stocks and annual straw C inputs. Our meta‐analysis using long‐term field experiments showed that SOC stock responses to straw return were greater than that of mineral fertilizers alone. Black soils with higher initial SOC stocks also had lower SOC stock increases than did soils with lower initial SOC stocks (fluvo‐aquic and loessial soils) following applications of nitrogen‐phosphorous‐potassium (NPK) fertilizer and NPK+S (straw). Soil C stocks under the NPK and NPK+S treatments increased in the more‐than‐20‐year duration period, while significant SOC stock increases in the NP and NP+S treatment groups were limited to the 11‐ to 20‐year period. Annual crop productivity was higher in double‐cropped wheat and maize under all fertilization treatments, including control (no fertilization), than in the single‐crop systems (wheat or maize). Also, the annual soil sequestration rates and annual straw C inputs of the treatments with straw return (NP+S and NPK+S) were significantly positively related. Moreover, initial SOC stocks and SOC sequestration rates of those treatments were highly negatively correlated. Thus, long‐term straw return integrated with mineral fertilization in upland wheat and maize croplands leads to increased crop yields and SOC stocks. However, those effects of straw return are highly dependent on fertilizer management, cropping system, soil type, duration period, and the initial SOC content.     

Contribution of winter cover crop amendments on global warming potential in rice paddy soil during cultivation

Background and aims

Winter cover crop cultivation during the fallow season has been strongly recommended in mono-rice paddy soil to improve soil quality, but its impact in increasing the greenhouse gases (GHGs) emissions during rice cultivation when applied as green manure has not been extensively studied. In order to recommend a preferable cover crop which can increase soil productivity and suppress GHG emission impact in paddy soil, the effect of winter cover crop addition on rice yield and total global warming potential (GWP) was studied during rice cultivation.

Methods

Two cover crops (Chinese milk vetch, Astragalus sinicus L., hereafter vetch, and rye, Secale cerealis) having different carbon/nitrogen (C/N) ratios were cultivated during the rice fallow season. The fresh above-ground biomasses of vetch [25 Mg fresh weight (FW) ha^?1, moisture content (MC) 86.9 %, C/N ratio 14.8] and rye (29 Mg rye FW ha^?1, MC 78.0 %, C/N ratio 64.3) were incorporated as green manure 1 week before rice transplanting (NPK + vetch, and NPK + rye). The NPK treatment was installed for comparison as the control. During the rice cultivation, methane (CH₄) and nitrous oxide (N₂O) gases were collected simultaneously once a week using the closed-chamber method, and carbon dioxide (CO₂) flux was estimated using the soil C balance analysis. Total GWP impact was calculated as CO₂ equivalents by multiplying the seasonal CH₄, CO₂, and N₂O fluxes by 25, 1, and 298, respectively.

Results

Methane mainly covered 79–81 % of the total GWP, followed by CO₂ (14–17 %), but the N₂O contribution was very small (2–5 %) regardless of the treatment. Seasonal CH₄ fluxes significantly increased to 61 and 122 % by vetch and rye additions, respectively, compared to that of the NPK treatment. Similarly, the estimated seasonal CO₂ fluxes increased at about 197 and 266 % in the vetch and rye treatments, respectively, compared with the NPK control plots. Based on these results, the total GWP increased to 163 and 221 % with vetch and rye applications, respectively, over the control treatment. Rice productivity was significantly increased with the application of green manure due to nutrient supply; however, vetch was more effective. Total GWP per grain yield was similar with the vetch (low C/N ratio) and NPK treatments, but significantly increased with the rye (high C/N ratio) application, mainly due to its higher CH₄ emission characteristic and lower rice productivity increase.

Conclusions

A low C/N ratio cover crop, such as vetch, may be a more desirable green manure to reduce total GWP per grain yield and to improve rice productivity.