Inclusion of upland crops in rice‐based rotations affects chemical properties of clay soil

In the Mekong Delta, alluvial clay soils have been used intensively over many generations for rice monoculture. Currently, farmers are confronted by problems of declining land productivity. Rotations comprising rice and upland crops can increase soil quality, but appropriate cropping systems for paddy soils have received relatively little attention. We therefore established a multiyear field experiment to evaluate the long‐term effects of cropping systems with different rotations on soil chemical quality. Systems laid out in a randomized complete block design with four replications were as follows: (i) traditional rice monoculture with three rice crops per year (R‐R‐R), (ii) rotation with two rice crops and maize (R‐M‐R), (iii) rotation with two rice crops and mung bean (R‐Mb‐R) and (iv) rotation with one rice crop and two upland crops – mung bean and maize (R‐Mb‐M). We hypothesized that systems with rotations of upland crops and their temporary beds improve chemical quality of paddy rice soil. Soil chemical parameters were determined to better understand and evaluate the sustainability of the cropping systems. Results showed an improvement in soil chemical quality for cropping systems with rotations of rice and mung bean or maize grown on temporary beds (R‐M‐R, R‐Mb‐R and R‐Mb‐M), particularly the content of soil organic carbon and a presumed hydrolysable labile carbon fraction compared with rice monoculture. Less pronounced improvements in EC, CEC and total acidity were also found with inclusion of upland crops. Cropping systems of rice with upland crops improved rice grain and straw yield in subsequent season in contrast with rice monoculture.     

Improving soil organic carbon pools through inclusion of summer mungbean in cereal-cereal cropping systems in Indo-Gangetic plain

Long-term effect of mungbean inclusion in lowland rice-wheat and upland maize-wheat systems on soil carbon (C) pools, particulate organic C (POC), and C-stabilization was envisaged in organic, inorganic and without nutrient management practices. In both lowland and upland systems, mungbean inclusion increased very-labile C (Cfrac₁) and labile C (Cfrac₂) in surface soil (0–0.2 m). Mungbean inclusion in cereal-cereal cropping systems improved POC, being higher in lowland (107.4%). Lowland rice-based system had higher passive C-pool (11.1 Mg C ha^?1) over upland maize-based system (6.6 Mg C ha^?1) indicating that rice ecology facilitates the stabilization of passive C-pool, which has longer persistence in soil. Organic nutrient management (farmyard manure + full crop residue + biofertilizers) increased Cfrac₁ and carbon management index (CMI) over inorganic treatment. In surface soil, higher CMI values were evident in mungbean included cropping systems in both lowland and upland conditions. Mungbean inclusion increased grain yield of cereal crops, and yield improvement followed the order of maize (23.7–31.3%) > rice (16.9–27.0%) > wheat (lowland 7.0–10.7%; upland 5.4–16.6%). Thus, the inclusion of summer mungbean in cereal-cereal cropping systems could be a long-term strategy to enrich soil organic C and to ensure sustainability of cereal-cereal cropping systems.     

Differences in soil organic carbon stocks and fraction distributions between rice paddies and upland cropping systems in China

Purpose

A large body of research suggests that rice (Oryza sativa L.) cropping facilitates soil organic carbon (SOC) storage, while the stability of the sequestered carbon is still not well understood. The objective of this study was to determine the differences in SOC stocks and fraction distributions between rice paddies and upland cropping fields and their variation in different rice cropping areas.

Materials and methods

Data from the national soil survey were analyzed to assess the differences in SOC contents between paddy and upland cropping fields at the regional scale. In addition, three pairs of rice and upland cropping systems were selected in Heilongjiang [single rice vs. single corn (Zea mays L.) cropping], Jiangsu [rice-wheat (Triticum aestivum L.) vs. corn-wheat cropping], and Jiangxi (double rice vs. double corn cropping) provinces, representing the major cropping patterns in China. Physical fractionation techniques were used to investigate the differences in SOC stocks and distribution among different pools between rice-based cropping systems and non-rice cropping systems in China.

Results and discussion

SOC concentrations were, on average, 74.9% higher at the regional scale and 56.8% higher at the field scale in paddy than in upland cropping fields. Carbon proportion of particulate organic matter within microaggregates increased from 14.4% in upland cropping soils to 25.3% in paddy soils at the Heilongjiang site and from 12.4 to 25.5% at the Jiangxi site. Meanwhile, the free silt and clay-associated carbon was significantly greater in paddy than in upland cropping soils at the both sites. Nevertheless, SOC distribution did not markedly differ between paddy and upland cropping fields at the Jiangsu site where rice was rotated with winter wheat annually.

Conclusions

As compared to upland cropping or rice-upland crop rotation, continuous rice cropping, such as single and double rice cropping, could favor SOC stabilization by occlusion within microaggregates and adsorption to the silt and clay outside microaggregates, which may promote the long-term storage of SOC in paddies.     

Effect of Cropping System on Physical Properties of Clay Soil Under Intensive Rice Cultivation

Cropping systems are thought to alter soil quality in paddy rice fields. This study was conducted to quantify the long‐term effects of continuous crop production under different cropping systems with different crop rotations on physical properties of alluvial clay soil in the Mekong Delta, Vietnam. Soil samples were collected from four treatments: (i) traditional intensive rice monoculture with three rice crops per year (R–R–R); (ii) rotation with two rice crops and maize (R–M–R); (iii) rotation with two rice crops and mung bean (R–Mb–R); and (iv) rotation with one rice and two upland crops, mung bean and maize (R–Mb–M). We hypothesized that cropping systems with rotations of upland crops and their temporary beds improve the physical quality of paddy rice soil; hence, they are better options towards sustainable agriculture. Results show an improvement of soil physical quality for systems with two rice crops and one upland crop (R–M–R and R–Mb–R) and those with one rice crop with two upland crops (R–Mb–M) compared with intensive rice monoculture (R–R–R). This was translated in decreased bulk density and soil strength, increased soil organic carbon and total porosity, and higher aggregate stability index, plant‐available water capacity, and Dexter's S index, especially at depths of 10–20 and 20–30 cm. The systems with different upland crops (maize or mung bean) showed similar high physical quality improvement. To maintain soil quality in future seasons, introducing a cropping system with at least one upland crop in rotation with rice is recommended. Copyright © 2014 John Wiley & Sons, Ltd.     

不同耕作方式下覆草旱作稻田土壤肥力的特征

通过始建于2003年中国南方季节性干旱区(江西省余江县)的双季稻田定位试验,于2005～2007年研究了水稻覆草旱作和免耕覆草旱作对稻田土壤理化性质和生物学性质的影响。结果表明,覆草旱作、免耕覆草旱作的耕层土壤容重和总孔隙度与常规水作的差异不显著。与常规水作相比,免耕覆草旱作显著提高土壤有机质、全氮、碱解氮和土壤基础呼吸;与常规水作相比,覆草旱作和免耕覆草旱作均显著提高土壤微生物生物量碳含量、脲酶和蔗糖酶活性。由此可知,覆草旱作和免耕覆草旱作可以作为该区积极推行的具有培肥地力作用的节水型稻作栽培模式。     

水旱轮作条件下免耕土壤微生物特性研究

通过野外调查和室内分析,研究了水旱轮作条件下,不同免耕年限土壤微生物数量和生物量的变化特点及其影响因素。结果发现:（1）旱作和水作后,免耕土壤细菌数量显著低于常规耕作。随着免耕年限延长,旱作后土壤细菌数量呈先降低再增加的趋势,免耕5～6 a时最低;而水作后,不同免耕年限间无显著差异。（2）旱作后,免耕土壤真菌和放线菌数量显著高于常规耕作,而水作后,真菌和放线菌数量较常规耕作显著降低。随着免耕年限的延长,旱作后土壤真菌数量呈先降低再增加的趋势,免耕7～8 a时最低;土壤放线菌数量在免耕5～6 a后趋于稳定。水作后,土壤真菌和放线菌数量呈显著负相关。（3）旱作和水作后,免耕土壤微生物量碳和氮显著高于常规耕作,两者呈极显著正相关,变化趋势一致。随着免耕年限延长,旱作后,土壤微生物量碳、氮呈逐渐降低的趋势;水作后,土壤微生物量碳、氮呈先增加再降低的趋势。     

Land use dynamics and nutrient characteristics of soils and plants along topo-sequences in inland valley watersheds of Ashanti region,Ghana

Surveys on land use dynamics were conducted over a 3-year period along various toposequences in benchmark inland valley watersheds of the Ashanti region, Ghana. Six typical land use systems were selected for more detailed studies, Le., primary forest (PF), cacao farm (CP), fallow (Fallow), mixed cropping (MC), and lowland rice-based systems including both traditional rice (TR) and sawah{ft1} (paddy)-based rice farming (Sawah). Topsoil samples (0-20 cm) and samples of leaves and bark of various plants were collected from these land use systems for nutrient characterization using laboratory analyses. The remaining primary and secondary forests cover only a patchy area, accounting for less than 20%, in forest reserves and surrounding areas. Cacao farms were developed both in the upland areas, middle slopes, and lowland areas, which occupied about 20% of the watershed. Lowland rice farming is estimated to account for about 10% of the watershed. Oil palm cultivation is also common in the lowland areas. The remaining land use systems were mostly fallow and mixed cropping of maize, cocoyam, cassava, and plantain. Plant leaves of various species in the lowland traditional rice area showed higher concentrations of phosphorus and potassium but lower calcium and strontium concentrations than those of the leaves in the upland surveyed plots, especially, the forest area. Nitrogen, sulfur, magnesium, and the other mineral elements, however, did not show any clear differences among the six land use systems. Bark samples tended to exhibit lower concentrations of nitrogen, phosphorus, sulfur, magnesium, sodium, silicon, aluminum, iron, manganese, and copper but higher concentrations of calcium and strontium. Cacao leaves showed silicon-accumulator characteristics and the magnesium concentration was high too. Cacao bark contained potassium and zinc in appreciable amounts in compared to the leaves. Topsoil samples of the primary forest and cacao farms in the upland areas showed higher levels of TC, TN, exchangeable Ca and Mg, and eCEC while the levels of available P showed a rather reverse trend compared to the lowland traditional and sawah rice plots. Topsoil samples of the fallow and mixed cropping plots at upland and fringe sites showed intermediate levels. The pH at the mixed cropping site was the lowest. These general fertility trends along upland and lowland topo-sequences were different from those of monsoon Asia and Japan. With the implementation of the sawah rice-based farming system, the inland valleys could contribute to the enhancement of sustainable food production in the country.     

稻作制度对红壤性水稻土有机质特征的影响

采用长期定位试验,比较3种稻作制度对红壤性水稻土有机质总量、有机无机复合状况、腐殖质结合形态、腐殖质组成、胡敏酸光学性质和总酸度等的影响。结果表明:冬泡制度比水旱轮作有助于增加土壤有机质总量、重组有机质含量、胡敏酸含量和胡敏酸/富啡酸,而水旱轮作比冬泡制度有利于提高土壤松结合态腐殖质、松结合态腐殖质/紧结合态腐殖质、胡敏酸E4值和总酸度。由此说明,冬泡制度有利于土壤有机质总量和胡敏酸的累积,但不利于胡敏酸分子的增长,腐殖质品质较差。而水旱轮作条件下土壤有机质活性增加,胡敏酸分子结构趋于复杂,其氧化度和芳香度增加。因此,通过周期性的水旱轮作换茬,可使土壤有机质的腐殖化和矿质化过程比例协调,从而提高土壤有机质的质量。     

Temporal Variation of Hydro‐Physical Properties of Paddy Clay Soil under Different Rice‐Based Cropping Systems

Spatial variability of hydro‐physical properties has long been observed, whereas temporal variation is much less documented and considered in studies and applications, particularly of paddy clay soils under different cropping systems. The objective of this study was therefore to assess the seasonal‐ and inter‐seasonal variation of selected hydro‐physical properties of a paddy clay soil under different rice‐based cropping systems with contrasting tillage. In a long‐term experiment, plots were arranged in a randomized complete block design with four treatments and four replications: (i) rice–rice–rice; (ii) rice–maize–rice; (iii) rice–mung bean–rice; and (iv) rice–mung bean–maize. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) at three times during two cropping seasons, i.e., 15 days after soil preparation (DASP), 45 DASP and 90 DASP during the winter–spring and spring–summer seasons. Results show that temporal variability of soil bulk density, macro‐porosity (MacP) and matrix‐porosity within both seasons and between seasons was limited for cropping systems with upland crop rotations, whereas within season variation was significant for rice monoculture system. Observed variation in bulk density, matrix‐porosity and MacP was mainly associated with cropping system and soil depth. Field saturated hydraulic conductivity of topsoil showed great temporal variability, both seasonal and inter‐seasonal, in correspondence with MacP (r  = 0·58). These results highlight the need of depth differentiated soil sampling and time consideration when evaluating management practices on soil physical properties and modeling the hydrological behavior of paddy soil. Copyright © 2017 John Wiley & Sons, Ltd.     

长期定位试验条件下红壤性水稻土有机质的变化

通过22年长期定位试验,研究了红壤性水稻土有机质的含量及其结合形态在3种稻作制、3种有机肥施用水平及2种地下水位深度条件下的长期演变规律,结果表明:红壤旱土改水田后,土壤有机质含量逐渐增加,各处理平均增长15.2gkg-1,增长率达98.9%。不同稻作制间,以稻—稻—冬泡处理土壤有机质增长幅度最大,21年共增加了18.0gkg-1,增长率达116.9%;稻—稻—冬绿处理次之,共分别增长15.8gkg-1和102.6%;稻—稻—冬油处理最低,仅分别增长11.9g kg-1和77.3%。不同有机肥施用水平间,以高量有机肥处理土壤有机质增长最快,21年共增加了17.9gkg-1,增长率为116.2%;常量有机肥处理次之,共分别增加16.1gkg-1和104.5%;化肥处理最低,共分别增加11.8gkg-1和76.6%。不同地下水位深度对土壤有机质积累的影响不显著。土壤腐殖质结合形态以紧结态为主,占腐殖质总量的50～70%,松结态腐殖质次之,占20～40%,稳结态腐殖质最少,仅5～11%。冬种处理土壤腐殖质的松/紧比大于冬泡处理。施用有机肥料能提高土壤腐殖质的松/紧比。     

Ecological study on the dynamics of soil organic matter and its related properties in shifting cultivation systems of Northern Thailand

Abstract

There is a large number of hill people in northern Thailand, who practices shifting cultivation. In order to analyze the soil ecological problems involved in the transition from traditional shifting cultivation to more intensive upland farming, the authors carried out comparative studies on the dynamics of organic matter and its related properties in soils both in the traditional shifting cultivation systems adopted by Karen people and more intensive upland farming practiced by Thai and Hmong people in the area. The contents of organic matter and available N in the surface 10 cm layers of soil from the fields continuously cultivated were lower than those in soils under prolonged fallow (more than 10 y) or natural forest. Based on the rate of soil respiration, the amount of organic matter decomposed within 1 y was estimated to reach nearly 10% of that stored in the upper 50 cm layers of the soil profile in the upland crop fields. These results indicate that the organic matter-related resources markedly decreased under continuous cropping. The contents of C, N, and P in the microbial biomass of the surface 10 cm layers of soil ranged from 0.37 to 2.09 mg C g^?l soil, from 22.7 to 188 µg N g^?l soil, and from 6.1 to 65.7 µg P g^?l soil, respectively. Since the contents of microbial C, N, and P in the surface soils were generally higher under prolonged fallow and natural forests than in the fields continuously cultivated, the microbial activity and/or the amounts of C, N, and P available for biological activity seemed to have declined under continuous upland farming. The incubation experiment to assess the N mineralization pattern showed two remarkable characteristics: 1) there was an initial time lag until active mineralization of N occurred in the soils from young fallow forest and 2) the soil burning effect was observed after burning in the fields under prolonged fallow. The active process of nitrification after N mineralization was always associated with a sharp fall in soil pH, suggesting that soil acidification was promoted and basic cations were lost from the soils. In conclusion, rapid deterioration of the soil organic matter-related properties in cropping fields can be considered to be one of the ecological reasons why upland fields must be returned to fallow again a few years after forest reclamation in traditional shifting cultivation systems. Therefore, in alternative farming systems with more intensive land use, it is essential to apply organic materials into soils to decrease the rate of soil degradation, or to improve the soil fertility, in avoiding soil acidification along with nitrification.     

不同干扰强度下农业生态系统土壤微生物生物量和活性的分异

Different management practices in six agroecosystems located near Goldsboro, NC, USA were conducted including a successional field (SU), a plantation woodlot (WO), an integrated cropping system with animals (IN), an organic farming system (OR), and two cash-grain cropping systems employing; either tillage (CT) or no-tillage (NT) to examine if and how microbial biomass and activity differ in response to alterations in disturbance intensity from six land management strategies. Results showed that soil microbial biomass and activity differed, with microbial activity in intermediately disturbed ecosystems (NT, OR, IN) being significantly higher (P < 0.01) than systems with either high or low disturbance intensities. There was also a significant and a highly significant ecosystem effect from the treatments on microbial biomass C (MBC) (P < 0.05) and on microbial activity (respiration) (P < 0.01), respectively. Multiple comparisons of mean respiration rates distinctly separated the six ecosystem types into three groups: CT < NT, SU and WO < OR and IN. Thus, for detecting microbial response to disturbance changes these results indicated that the active component of the soil microbial community was a better indicator than total biomass.     

水稻-番茄轮作植物寄生线虫及微生物群落结构差异

土壤线虫和微生物群落结构与作物健康密切相关。采用田间试验，利用传统分类和高通量测序技术，研究了水稻–番茄轮作(FS)、番茄连作(FF)和休耕(CK)3种种植制度土壤线虫及微生物群落结构差异。结果表明，水旱轮作土壤中线虫种类少，自由生活线虫占比高。土壤中植物寄生线虫属的检出率，轮作最少，仅有5个，连作最多，共13个，且大部分为常见属；水旱轮作同时能降低土壤中植物寄生线虫的种类，包括主要危害番茄的根结线虫属，占比仅2.1%，而连作为29.7%。不同种植制度下真菌和细菌类群OUTs和群落结构差异明显；与连作相比，轮作和休耕真菌、细菌种群丰富度更高，共享占比更多，群落构成更相近；水旱轮作Alpha多样性指数显著高于连作；轮作土壤中植物寄生线虫拮抗微生物类群Chaetomium,Talaromyces,Anaerolineaceae和Acidobacteria相对丰度高于连作。水稻–番茄轮作能大幅减少植物寄生线虫种类，增加微生物群落多样性，改善土壤质量，是番茄生产中防控线虫病害的理想措施。     

Tillage and cropping effects on selected properties of an Argiudoll in Argentina

Abstract

Soils of the Argentine humid pampa region are usually weakly structured due to its high silt content. Selecting crop sequence or tillage systems are an alternative in small farms for the protection of the soil against physical degradation and erosion given that conservation practices, grass meadows, and fertilizers are expensive and therefore rarely used. Evaluation of selected soil properties was conducted on soil sampled from a long‐term tillage experiment with continuous soybean established in 1975 on a Typic Argiudoll silty loam soil in Argentina. Tillage treatments included conventional tillage with moldboard plow (CT), chisel plow (CP), and no till (NT). A comparison with continuous corn under NT was also carried out. Sampling was performed after the emergence of both crops in 1990. Tillage and cropping treatments affected properties related to soil slacking and dispersion to a greater extent than they did on aggregate size distribution. According to the De Leenheer and De Boodt index, aggregate stability within soybean soil classified as bad for CT, unsatisfactory for CP, and very good for NT, whereas the soil with corn under NT classified as excellent. The no tillage treatment within soybean had significantly more organic carbon in the 0–5 cm depth than CP or CT. Soil respiration was significantly higher in NT than in CT in the surface layer, while CT showed higher values in the 10–15 cm depth. Tillage treatments did not significantly affect microbial biomass under soybean cropping. The effect of monoculture corn versus monoculture soybean under NT on soil respiration, biomass and organic carbon was not significant. Soil pH in the 0–5 cm depth under soybean was in the order NT > CP > CT, whereas the soil with corn under NT was more acid than the soybean soil (P=0.05). Cation exchange capacity and exchangeable bases followed a similar trend. Organic carbon (0–5 cm depth) and aggregate stability were significantly correlated when samples from all treatments were considered.     

Soil carbon balance of rice-based cropping systems of the Indo-Gangetic Plains

An agricultural land use system centred on rice-based cropping systems as common in the Indo-Gangetic Plains (IGP), with its annual cycles of wet and dry, puddling and ploughing, is unique and exerts a specific influence on soil organic matter (SOM) dynamics. Reports of yield ‘stagnation’ in some parts of the IGP with a decline in SOM quantity and quality raises concerns about the sustainability of the rice-wheat system in the region. Proper understanding of the soil carbon balance and of measures required to build up or maintain the soil carbon status of such a production system is therefore important for its sustainable production. Long-term experiments conducted in this region are especially useful in gaining understanding of soil carbon dynamics, since the processes affecting carbon dynamics are slow in nature. We used a simple analytical model—Yang's model—to calculate carbon balances in the rice-based cropping systems of the IGP in India. We used eight data sets from rice-based cropping systems from different sub-regions in the IGP, with different crop managements applied to rice, wheat or a third crop. Carbon input into the soil from crop biomass was calculated using data on crop yield and Harvest Index (HI). The values of soil organic carbon content predicted by the model were comparable to the observed values (r = 0.91). The model performs well in situations with porous soils (low clay content), with a pH values in the neutral range (7-7.5) and low annual rainfall as in the situation of Ludhiana-1 and 2. However, it underperforms in situations with heavy clay soils with high rainfall, causing severe anaerobic conditions. The model projections for the long-term (by 2080) show a decline in SOC at all sites in the IGP. Hence, the yield stagnation in the IGP, which has been attributed to a decline in SOC and the associated reduction in nutrient supply, could lead to further decreases in SOC levels, aggravated by climate change-induced higher temperatures.     

以水稻为主的种植系统对土壤有机质状况的影响

A long-term simulation experiment was carried out to study the effect of rice-based cropping system, green manure and ground-water level on soil organic matter. Soil organic matter content increased when upland soil was puddled and cropped under submerged conditions. Among all treatments, soil organic matter contents in the treatments of rice-rice-flooded fallow in winter (WF) were the highest, those in the treatments of rice-rice-astragalus (WG) came the second, and those in the treatments of rice-rice-rape (WR) were the lowest. At the same rate of green manure application, the degrees of organo-mineral complexing in soils of treatments WG and WR were higher than those of treatment WF. After 9-year rice cultivation, the state of combination of humus in heavy fraction varied with treatments. The relative content of loosely bonded humus decreased in the order of WR > WG > WF, and it correlated significantly with Se availability.     

多样化种植对提升耕地质量的作用：进展与展望

多样化种植是现代生态农业的重要举措之一,对提高生物多样性、生态服务功能和土壤质量等具有重要意义。在全球粮食供给紧张和耕地短缺背景下,多样化种植在提升我国耕地质量和保障粮食安全中将会发挥越来越重要的作用。但现有研究对多样化种植的理解多集中在提高生物多样性和发挥生态功能等方面,对其提升耕地质量的作用关注较少,特别是多样化种植如何通过改善土壤物理、化学、生物多样性来提高耕地质量和维持土壤健康方面的理解还较为局限。本文在总结多样化种植的内涵及对促进耕地土壤健康和提高生态服务功能作用的基础上,系统梳理了多样化种植对改善土壤物理、化学、生物多样性等方面的作用研究进展,展望了未来以提升耕地质量为核心发展多样化种植亟需关注的方向和研究重点,以期为多样化种植在我国耕地质量提升策略中发挥更大作用提供参考。     

Impact of perennial pasture and tillage systems on carbon input and soil quality indicators

Soil degradation associated with tillage is a major problem in Uruguayan agriculture. Either rotation of crops with pastures (ROT) or no-till (NT) cropping have been proposed as alternatives to minimize the impact of agriculture on soil quality. The combined impact on soil properties of ROT and NT has not been evaluated. In this study, we report results of the first 12 years of a long-term experiment established on a clay loam soil in western Uruguay. The objective was to determine the influence of conventional tillage (CT) and NT on systems under continuous cropping (CC, two crops per year) or ROT (3.5-year annual crops/2.5-year pastures). Soil samples taken at the beginning of the experiment in 1994 and in 2004 were analyzed for organic carbon (SOC), total organic carbon (TSOC) and total nitrogen content (STN), and for water-stable aggregation (WAS). Soil loss and erodibility indicators were studied using microrain simulator. With 12 years, the cumulative carbon (C) inputs of aboveground biomass were similar between tillage, but C input in CC was 50% higher than ROT. This difference was explained because 84% of the pastures dry matter was consumed by animals. Nevertheless we estimated a higher below ground biomass in ROT compared to CC systems (24.9 Mg ha⁻¹ vs. 10.9 Mg ha⁻¹). NT presented 7% higher SOC than CT (0–18 cm) with no differences between rotation systems. While all treatments declined in STN during 12 years, ROT had 11% and 58% higher STN and WAS than CC systems, with a large impact of the pasture under CT. Runoff and erosion were minimized under NT in both rotations systems. Thus, including pastures in the rotation, or switching from CT to NT improved soil quality properties. The expected benefit of combining NT and ROT will likely require more years for the cumulative effect to be detectable in both C input and soil properties.     

Soil microbial biomass and nitrogen supply in an irrigated lowland rice soil as affected by crop rotation and residue management

 Processes that govern the soil nitrogen (N) supply in irrigated lowland rice systems are poorly understood. The objectives of this paper were to investigate the effects of crop rotation and management on soil N dynamics, microbial biomass C (C_BIO) and microbial biomass N (N_BIO) in relation to rice N uptake and yield. A maize-rice (M-R) rotation was compared with a rice-rice (R-R) double-cropping system over a 2-year period with four cropping seasons. In the M-R system, maize (Zea mays L.) was grown in aerated soil during the dry season (DS) followed by rice (Oryza sativa L.) grown in flooded soil during the wet season (WS). In the R-R system, rice was grown in flooded soil in both the DS and WS. Three fertilizer N rates (0, 50 or 100 kg urea-N ha^–1 in WS) were assigned to subplots within the cropping system main plots. Early versus late crop residue incorporation following DS maize or rice were established as additional treatments in sub-subplots in the second year. In the R-R system, the time of residue incorporation had a large effect on NO₃ ^–-N accumulation during the fallow period and also on extractable NH₄ ⁺-N, rice N uptake and yield in the subsequent cropping period. In contrast, time of residue incorporation had little influence on extractable N in both the fallow and rice-cropping periods of the M-R system, and no detectable effects on rice N uptake or yield. In both cropping systems, C_BIO and N_BIO were not sensitive to residue incorporation despite differences of 2- to 3-fold increase in the amount of incorporated residue C and N, and were relatively insensitive to N fertilizer application. Extractable organic N was consistently greater after mid-tillering in M-R compared to the R-R system across N rate and residue incorporation treatments, and much of this organic N was α-amino N. We conclude that N mineralization-immobilization dynamics in lowland rice systems are sensitive to soil aeration as influenced by residue management in the fallow period and crop rotation, and that these factors have agronomically significant effects on rice N uptake and yield. Microbial biomass measurements, however, were a poor indicator of these dynamics. Received: 31 October 1997     

稻田系统管理措施对微生物生物量C、N、P的长期影响

A 12-year field experiment was conducted to investigate the effect of different tillage methods and fertil-ization systems on microbial biomass C,N and P of a gray fluvo-aguic soil in rice-based cropping system .Five fertilization treatments were designed under conventional tillae(CT) or on tillage(NT) system:no fertilizer(CK) ; chemical fertilizer only(CF) ; combining chemical fertilizer with pig manure(PM); combining chemical fertilizer with crop straw (CS) and fallow (F). The results showed that biomass C,N and P were enriched in the surface layer of no-tilled soil,whereas they distributed relatively evenly in the tilled soil,which might result from enrichment of crop resdue,organic manure and mineral fertilzer,and surficial developent of root systems under NT.Under the cultivation system NT had slightly greater biomass C,N and P at 0-5 cm depth ,significantly less biomass C,N and P at 5-15 cm depth ,less microbial biomass C,N and equivalent biomass P at 15-30 cm depth as compared to CT,indicating hat tillage was beneficial for the multiplication of organims in the plowed layer of soil.Under the fallow system,biomass C,N and P in the surface layer were significantly greater for NT than CT while their differences between the two tillage methods were neligible in the deeper layers.In the surface layer,biomass C,N and P in the soils amended with oranic manure combined with mineral fertilizers were significantly greater than those of the treatments only with mineral fertilizers and the control.Soils without fertilzer had the least biomass nutrient contents among the five fertilization treatments.Obviously,the long-term application of organic manure could maintain the higher activity of microorganisms in soils.The amounts of biomass C,N and P in the fallowed soils varied with the tillage methods;they were much greater under NT than under CT,especially in the surface layer,suggesting that the frequent plowing could decrease the content of organic matter in the surface layer of the fallowed soil.