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1.
Crop residues and manure are important sources of carbon (C) for soil organic matter (SOM) formation. Crop residue return increases by nitrogen (N) fertilization because of higher plant productivity, but this often results only in minor increases of SOM. In our study, we show how N fertilization and organic C additions affected SOM and its fractions within a 32‐year‐long field‐experiment at Puch, Germany. Five organic additions, no‐addition (control), manure, slurry, straw and straw + slurry, were combined with three mineral N fertilization rates (no, medium and high fertilization), which resulted in 1·17–4·86 Mg C‐input ha‐1 y‐1. Topsoil (0–25 cm) SOM content increased with N fertilization, mainly because of the C in free light fraction (f‐LF). In contrast, subsoil (25–60 cm) SOM decreased with N fertilization, probably because of roots' relocation in Ap horizon with N fertilization at the surface. Despite high inputs, straw contributed little to f‐LF but prevented C losses from the mineral‐associated SOM fraction (ρ > 1·6 g cm‐3) with N fertilization, which was observed without straw addition. Above (straw) and belowground (roots) residues had opposite effects on SOM fractions. Root C retained longer in the light‐fractions and was responsible for SOM increase with N fertilization. Straw decomposed rapidly (from f‐LF) and fueled the mineral‐associated SOM fraction. We conclude that SOM content and composition depended not only on residue quantity, which can be managed by the additions and N fertilization, but also on the quality of organics. This should be considered for maintaining the SOM level, C sequestration, and soil fertility. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

2.
Conversion of natural forest to agricultural land use has significantly lowered the soil organic matter (SOM) content in sandy soils of northeast Thailand. This paper reviews the findings of comparative studies on contents of SOM pools (labile, i.e. microbial biomass and particulate organic matter—POM and stable, i.e. humic substance) and related soil aggregate formation, in natural forest plots and cultivated fields (monocrops of cassava, sugarcane and rice) in sites representative of northeast Thailand from the viewpoints of terrain (i.e. undulating), soils (sandy) and land use and discusses the restoration of SOM and fertility (nitrogen) in these degraded soils. Monocultural agriculture brings about the degradation of all SOM pools and associated soil aggregation as compared to the forest system because of decreased organic inputs and more frequent soil disturbance. The build‐up of SOM was achieved through the continuous recycling of organic residues produced within the system. Low‐quality residues contributed the largest SOM build‐up in whole and fractionated SOM pools, including POM and humic substance. However, to restore N fertility, high quality residues, (i.e. with low C/N ratios, lignin and polyphenols) were also needed. Timing of N release to meet crop demand was achieved by employing a mixture of high and low quality residues. Selection of appropriate residues for N sources was affected by environmental factors, notably soil moisture regimes, which differed in upland field and lowland paddy subsystems. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
Abstract. Predictive, regional use of soil organic matter (SOM) models requires evaluation of the performance of models with datasets from long‐term experiments relevant to the scenarios of interest to the regional scale study, and relevant to the climate of the study region. Datasets from six long‐term experiments were used to evaluate the performance of RothC and CENTURY, two of the most widely used and tested SOM models. Three types of model run were completed for each site: (1) CENTURY model alone; (2) RothC model run to fit measured SOC values, by iteratively adjusting C inputs to soil; and (3) RothC model run using C inputs derived from CENTURY runs. In general, the performance of both models was good across all datasets. The runs using RothC (iteratively changing C inputs to fit measured SOC values) tended to have the best fit to model data, since this method involved direct fitting to observed data. Carbon inputs estimated by RothC were, in general, lower than those estimated by CENTURY, since SOC in CENTURY tends to turn over faster than SOC in RothC. The runs using RothC with CENTURY C inputs tended to have the poorest fit of all, since CENTURY predicted greater C inputs than were required by RothC to maintain the same SOC content. A plausible model fit to measured SOC data may be obtained with widely differing C input values, due to differences in predicted decomposition rates between models. It remains unclear which, if either, modelling approach most closely represents reality since both C inputs to soil and decomposition rates for bulk SOM are difficult to determine experimentally. Further progress in SOM modelling can only be the result of research leading to better process understanding, both of net C inputs to soil and of SOM decomposition rates. The use of default methods for estimating initial SOC pools in RothC and CENTURY may not always be appropriate and may require adjustment for specific sites. The simulations presented here also suggest details of SOC dynamics not shown by available measured data, especially trends between sampling intervals, and this emphasizes the importance of archived soil samples in long‐term experiments.  相似文献   

4.
Soil tillage has been shown to affect long‐term changes in soil organic carbon (SOC) content in a number of field experiments. This paper presents a simplified approach for including effects of tillage in models of soil C turnover in the tilled‐soil layer. We used an existing soil organic matter (SOM) model (CN‐SIM) with standard SOC data for a homogeneous tilled layer from four long‐term field experiments with conventionally tilled (CT) and no‐till (NT) treatments. The SOM model was tested on data from long‐term (>10 years) field trials differing in climatic conditions, soil properties, residue management and crop rotations in Australia, Brazil, the USA and Switzerland. The C input for the treatments was estimated using data on crop rotation and residue management. The SOM model was applied for both CT and NT trials without recalibration, but incorporated a ‘tillage factor’ (TF) to scale all decomposition and maintenance parameters in the model. An initial value of TF = 0.57 (parameter uncertainty, PU = 0.15) for NT (with TF set to 1.0 for CT) was used on the basis of a previous study with observations of soil CO2 respiration. The simulated and observed changes in SOC were then compared using slopes of linear regressions of SOC changes over time. Results showed that the SOM model captured observed changes in SOC content from differences in rotations, N application and crop residue management for conventional tillage. On the basis of SOC change data a mean TF of 0.48 (standard deviation, SD = 0.12) was estimated for NT. The results indicate that (i) the estimated uncertainty of tillage effects on SOC turnover may be smaller than previously thought and (ii) simple scaling of SOM model parameters may be sufficient to capture the effects of soil tillage on SOM turnover in the tilled layer. Scenario analyses showed that the average extra C input needed to compensate for soil tillage was 762 (SD = 351) kg C ha−1 year−1. Climatic conditions (temperature and precipitation) also affected how much extra C was needed, with substantially larger inputs being required for wetter and warmer climates.  相似文献   

5.
Crop and land management practices affect both the quality and quantity of soil organic matter (SOM) and hence are driving forces for soil organic carbon (SOC) sequestration. The objective of this study was to assess the long‐term effects of tillage, fertilizer application and crop rotation on SOC in an agricultural area of southern Norway, where a soil fertility and crop rotation experiment was initiated in 1953 and a second experiment on tillage practices was initiated in 1983. The first experiment comprised 6‐yr crop rotations with cereals only and 2‐yr cereal and 4‐yr grass rotations with recommended (base) and more than the recommended (above base) fertilizer application rates; the second experiment dealt with autumn‐ploughed (conventional‐till) plots and direct‐drilled plots (no‐till). Soil samples at 0–10 and 10–30 cm depths were collected in autumn 2009 and analysed for their C and N contents. The quality of SOM in the top layer was determined by 13C solid‐state NMR spectroscopy. The SOC stock did not differ significantly because of rotation or fertilizer application types, even after 56 yr. However, the no‐till system showed a significantly higher SOC stock than the conventional‐till system at the 0–10 cm depth after the 26 yr of experiment, but it was not significantly different at the 10–30 cm depth. In terms of quality, SOM was found to differ by tillage type, rate of fertilizer application and crop rotation. The no‐till system showed an abundance of O‐alkyl C, while conventional‐till system indicated an apparently indirect enrichment in alkyl C, suggesting a more advanced stage of SOM decomposition. The long‐term quantitative and qualitative effects on SOM suggest that adopting a no‐tillage system and including grass in crop rotation and farmyard manure in fertilizer application may contribute to preserve soil fertility and mitigate climate change.  相似文献   

6.
Conventional agricultural practices that use excessive chemical fertilizers and pesticides come at a great price with respect to soil health, a key component to achieve agricultural sustainability. Organic farming could serve as an alternative agricultural system and solve the problems associated with the usage of agro‐chemicals by sustainable use of soil resources. A study was carried out to evaluate the impact of organic vs . conventional cultivations of basmati rice on soil health during Kharif (rainy) season of 2011 at Kaithal district of Haryana, India, under farmers' participatory mode. Long‐term application of organic residues in certified organic farms was found to improve physical, chemical, and biological indicators of soil health. Greater organic matter buildup as indicated by higher soil organic carbon content in organic fields was critical to increase soil aggregate stability by increasing water holding capacity and reducing bulk density. Proper supplementation of nutrients (both major and micro nutrients) through organic residue addition favored biologically available nutrients in organic systems. Further, the prevalence of organic substrates stimulated soil microorganisms to produce enzymes responsible for the conversion of unavailable nutrients to plant available forms. Most importantly, a closer look at the relationship between physicochemical and biological indicators of soil health evidenced the significance of organic matter to enzyme activities suggesting enhanced nutrient cycling in systems receiving organic amendments. Enzyme activities were very sensitive to short‐term (one growing season) effects of organic vs . conventional nutrient management. Soil chemical indicators (organic matter and nutrient contents) were also changed in the short‐term, but the response was secondary to the biochemical indicators. Taken together, this study indicates that organic farming practices foster biotic and abiotic interactions in the soil which may facilitate in moving towards a sustainable food future.  相似文献   

7.
Soil degradation resulting from permanent and high pressure on natural resources is a threat for the present and future of agricultural production in Ethiopia. Mono‐cropping, cultivation on steep slopes, use of cattle manure and crop residues as an energy source for cooking are common practices that have led to declining soil organic matter (SOM) contents. The objective of this research was to evaluate the current status of SOM in farmlands and exclosures (areas protected from grazing to allow their natural restoration) in Northern Ethiopia and to explore the long‐term effects of current agricultural practices and an improved scenario on SOM. At present, the SOM content of farmland soils is small, ranging from 2.1% to 2.9%, while exclosures showed a significant recovery after 20 yr of protection, with SOM contents ranging from 2.6% to 5.6%. However, the level of SOM in farmland soils is envisaged to decline given current agricultural practices, that is removal of crop residues and use of manure as an energy source for cooking. We found that applying manure alone appeared to be insufficient to revert this trend, due to limited availability and its alternative uses. Therefore, a multidisciplinary approach including improved manure and compost management needs to be supplemented with energy saving techniques, as fuel use is currently the largest competing claim for organic matter in the area.  相似文献   

8.
The utilization of treated paper mill effluents for irrigation offers many benefits such as conservation of water resources, conversion of barren land into irrigated area, addition of nutrients to the soil and plant and above all the reduction of pollution of inland water bodies. However, the utility of this effluent irrigation programme depends mainly on farmers' acceptability, adoption and management of the scheme. Knowledge about the farmers' perception is thus very much imperative for further advocacy of the effluent irrigation programme. The determinants of farmers' perception of treated paper mill effluent irrigation is a pre‐requisite for the formulation of better programmes and strategies for the support of an unobstructed adoption and for the long‐term sustainability of effluent irrigation schemes. The present study was conducted to assess the farmers' perception and the determinants that influence the adoption of treated paper mill effluent irrigation by interviewing a random sample of 120 farmers, using a well‐structured interview schedule in paper mill effluent irrigated area in Tamil Nadu in India. The study revealed that there exists positive significant correlation between the perception and the characteristics of the farmers viz. educational status, farm size, annual income, mass media exposure, innovativeness and risk orientation. The response analysis of the perception revealed that treated paper mill effluent as alternative assured supply of irrigation water, conversion of elevated dry lands to irrigated land, changing of cropping pattern to sugarcane, increase in socioeconomic status of the farmers, incentives and technical inputs by the paper mill authorities and above all farmers' participation in planning, implementation and management of the effluent irrigation schemes influenced the farmers to form positive perception. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
Berpura alluvial soil series of the Indo‐Gangetic Plains is situated in the Ambala District of the Haryana State of India. Soils of this series had medium concentrations of both potassium (K) and phosphorus (P) and large concentrations of sulfur (S) before 1970. To study different fractions of K, Olsen P, and 0.15% calcium chloride (CaCl2)–extractable (available) S of soils of the Berpura series and to create nutrient indexing of rice crops growing on this series, surface soil samples were collected from 100 farmers' fields after the harvest of the wheat crop in 2005. During kharif season of same year, samples of upper two leaves at anthesis growth stage of rice crop were also collected from the same 100 farmers' fields that had earlier been sampled for soil analysis. Analysis of soil samples showed more K depletion in soils of this series, of which 86% of farmers' fields were deficient in ammonium acetate (NH4OAc) K (available K). Thirty and 62% of leaf samples of the rice crop growing on the 100 fields of this series were extremely and moderately deficient in K, respectively. The mean values of water‐soluble, exchangeable, nonexchangeable, lattice, and total K were 10.6, 30.3, 390.0, 8204, and 8635 mg kg?1, respectively. In soils of this series, 0.123, 0.351, 4.517, and 95.009% of total K were found in water‐soluble, exchangeable, nonexchangeable, and lattice K forms, respectively. On the other hand, long‐term farmers' practice of more application of P fertilizer in wheat crop has resulted in P buildup in the soils of the Berpura series. Olsen P in soils of farmers' fields of this series ranged from 9.0 to 153.0 mg kg?1, with the mean value of 41.8 mg kg?1. Eighty‐two percent of leaf samples of rice crops grown on this series without application of P fertilizer were sufficient in P. The analysis of soil and rice crops for P and K proved the suitability of 0.5 M sodium bicarbonate (NaHCO3) and 1 N NH4OAc for extracting available P and K, respectively, in alluvial soils of the Indo‐Gangetic Plains. The 0.15% CaCl2–extractable S in this soil ranged from 9.6 to 307 mg kg?1 with a mean value of 34.6 mg kg?1. Four and 26% of soil samples had low and medium, respectively, in 0.15% CaCl2–extractable S. S deficiency was recorded in rice crops, as 29% of the leaf samples were extremely deficient in S and 58% were moderately deficient in S. This indicated the unsuitability of the 0.15% CaCl2 to extract available S from the Udic ustochrept utilized for cultivation of rice crops.  相似文献   

10.
Nitrogen (N) and phosphorus (P) deficiencies are key constraints in rainfed lowland rice (Oryza sativa L.) production systems of Cambodia. Only small amounts of mineral N and P or of organic amendment are annually applied to a single crop of rainfed lowland rice by smallholder farmers. The integration of leguminous crops in the pre‐rice cropping niche can contribute to diversify the production, supply of C and N, and contribute to soil fertility improvement for the subsequent crop of rice. However, the performance of leguminous crops is restricted even more than that of rice by low available soil P. An alternative strategy involves the application of mineral P that is destined to the rice crop already to the legume. This P supply is likely to stimulate legume growth and biological N2 fixation, thus enhancing C and N inputs and recycling N and P upon legume residue incorporation. Rotation experiments were conducted in farmers' fields in 2013–2014 to assess the effects of P management on biomass accumulation and N2 fixation (δ15N) by mungbean (Vigna radiata L.) and possible carry‐over effects on rice in two contrasting representative soils (highly infertile and moderately fertile sandy Fluvisol). In the traditional system (no legume), unamended lowland rice (no N, + 10 kg P ha?1) yielded 2.8 and 4.0 t ha?1, which increased to 3.5 and 4.7 t ha?1 with the application of 25 kg ha?1 of urea‐N in the infertile and the moderately fertile soil, respectively. The integration of mungbean as a green manure contributed up to 9 kg of biologically fixed N (17% Nfda), increasing rice yields only moderately to 3.5–4.6 t ha?1. However, applying P to mungbean stimulated legume growth and enhanced the BNF contribution up to 21 kg N ha?1 (36% Nfda). Rice yields resulting from legume residue incorporation (“green manure use”–all residues returned and “grain legume use”–only stover returned) increased to 4.2 and 4.9 t ha?1 in the infertile and moderately fertile soil, respectively. The “forage legume use” (all above‐ground residues removed) provided no yield effect. In general, legume residue incorporation was more beneficial in the infertile than in the moderately fertile soil. We conclude that the inclusion of mungbean into the prevailing low‐input rainfed production systems of Cambodia can increase rice yield, provided that small amounts of P are applied to the legume. Differences in the attributes of the two major soil types in the region require a site‐specific targeting of the suggested legume and P management strategies, with largest benefits likely to accrue on infertile soils.  相似文献   

11.
Soil quality (SQ) assessment from farmers' point of view can be used as a primary indicator for planning sustainable agriculture. Despite this fact, limited information is documented with regard to SQ indicators, for example weed species, crop types and management practices from farmers' knowledge perspectives. The aims of this study are to analyse factors that determine farmers' knowledge of SQ, identify SQ indicators of weed species and crop types across different SQ status and assess soil‐and‐crop management practices that maintain SQ in the Mai‐Negus catchment, northern Ethiopia. Fifty‐two farmer household heads were chosen randomly for questionnaire interview. The results showed significant (p ≤ 0·05) differences in the proportion of respondents who used different crop‐and‐soil management practices. The success of overall prediction by the logistic regression model (model χ2 = 0·84, p < 0·01) and level of model correct predictions (86%) indicated that the explanatory variables have sufficiently explained farmers' knowledge of SQ indicators. Provided that other conditions remained constant, the odds ratio of variables such as farmer experience, access to information, farm location, education, field slope and land tenure have significantly increased the likelihood of farmers for being knowledgeable of SQ indicators. This study also demonstrated that most farmers are knowledgeable in identifying weed species, crop types and management practices across various SQ status, which suggests that such SQ indicators should be used to assess SQ status (degradation severity) while locating fields to be intervened using appropriate management strategies. © 2013 The Authors. Land Degradation & Development published by John Wiley & Sons, Ltd.  相似文献   

12.
The following study was conducted to determine smallholders' land use management practices and agricultural indicators of soil quality within farmers' fields in Chuka and Gachoka divisions in Kenya's Central Highlands. Data on cropping practices and soil indicators were collected from farmers through face‐to‐face interviews and field examinations. Farmers characterised their fields into high and low fertility plots, after which soils were geo‐referenced and sampled at surface depth (0–20 cm) for subsequent physical and chemical analyses. Farmers' indicators for distinguishing productive and non‐productive fields included crop yield, crop performance and weed species. Soils that were characterised as fertile, had significantly higher chemical characteristics than the fields that were of poor quality. Fertile soils had significantly higher pH, total organic carbon, exchangeable cations and available nitrogen. Factor analysis identified four main factors that explained 76 per cent of the total variance in soil quality. The factors were connected with farmers' soil assessment indicators and main soil processes that influenced soil quality in Central Kenya. Soil fertility and crop management practices that were investigated indicated that farmers understood and consequently utilised spatial heterogeneity and temporal variability in soil quality status within their farms to maintain and enhance agricultural productivity. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

13.
The aim of this study was to evaluate the interaction between yield levels of nonleguminous crops and soil organic matter (SOM) under the specific conditions of organic and conventional farming, respectively, and to identify implications for SOM management in arable farming considering the farming system (organic vs. conventional). For that purpose, correlations between yield levels of nonlegume crops and actual SOM level (Corg, Nt, Chwe, Nhwe) as well as SOM‐level development were examined including primary data from selected treatments of seven long‐term field experiments in Germany and Switzerland. Yield levels of nonlegume crops were positively correlated with SOM levels, but the correlation was significant only under conditions of organic farming, and not with conventional farming treatments. While absolute SOM levels had a positive impact on yield levels of nonlegumes, the yield levels of nonlegumes and SOM‐level development over time correlated negatively. Due to an increased demand of N from SOM mineralization, higher yield levels of nonlegumes obviously indicate an increased demand for OM supply to maintain SOM levels. Since this observation is highly significant for farming without mineral‐N fertilization but not for farming with such fertilization, we conclude that the demand of SOM‐level maintenance or enhancement and thus adequate SOM management is highly relevant for crop production in organic farming both from an agronomical and ecological point of view. Under conventional management, the agronomic relevance of SOM with regard to nutrient supply is much lower than under organic management. However, it has to be considered that we excluded other possible benefits of SOM in our survey that may be highly relevant for conventional farming as well.  相似文献   

14.
Despite the importance of soil organic matter (SOM), very few long‐term data concerning soil organic‐C dynamics are available for calibrating and evaluating C models. The long‐term 14C‐turnover field experiment, established in 1967 in Fuchsenbigl, Lower Austria, offers the unique opportunity to follow the fate of labeled C under different crop‐management systems (bare fallow, spring wheat, crop rotation) over a period of more than 35 y. Compared with the crop‐rotation and spring‐wheat treatments, the decline of total organic C was largest in the bare‐fallow treatments, because no significant C input has occurred since 1967. Nonetheless, the decline was not as fast as predicted with the original RothC‐26.3‐model decomposition rate constants. In this work, we therefore calibrated the Roth‐C‐26.3 model for the Pannonian climatic region based on the field‐experiment results. The main adjustment was in the decomposition rate constant for the humified soil C pool (HUM), which was set to 0.009 instead of 0.02 y–1 as determined in the original Rothamsted field trial. This resulted in a higher HUM pool in the calibrated model because of a longer turnover period (111 vs. 50 y). The modeled output based on the calibrated model fitted better to measured values than output obtained with the original Roth‐C‐26.3‐model parameters. Additionally, the original decomposition rate constant for resistant plant material (RPM) was changed from 0.3 to 0.6 y–1 to describe the decomposition of 14C‐labeled straw more accurately. Application of the calibrated model (modified HUM decomposition rate) to simulate removal of crop residues showed that this can entail a long‐term decline of SOM. However, these impacts are strongly dependent on the crop types and on environmental conditions at a given location.  相似文献   

15.
Organic inputs [e.g. animal manure (AM) and plant residues] contribute directly to the soil organic N pool, whereas mineral N fertilizer contributes indirectly by increasing the return of the crop residues and by microbial immobilization. To evaluate the residual effect of N treatments established in four long‐term (>35 yr) field experiments, we measured the response of barley (grain yield and N offtake at crop maturity) to six rates (0, 30, 60, 90, 120 and 150 kg N/ha) of mineral fertilizer N (Nnew) applied in subplots replacing the customary long‐term plot treatments of fertilizer inputs (Nprev). Rates of Nprev above 50–100 kg N/ha had no consistent effect on the soil N content, but this was up to 20% greater than that in unfertilized treatments. Long‐term unfertilized plots should not be used as control to test the residual value of N in modern agriculture with large production potentials. Although the effect of mineral Nprev on grain yield and N offtake could be substituted by Nnew within a range of previous inputs, the value of Nprev was not eliminated irrespective of Nnew rate. Provided a sufficient supply of plant nutrients other than N, the use‐efficiency of Nnew did not change significantly with previous mineral N fertilizer rate. The residual effect of mineral N fertilizer was negligible compared with the residual effect of N from AM and catch crop residues.  相似文献   

16.
Models are important for predicting how soil organic carbon alters with changing environment and management. We tested three different ways of parameterizing the Rothamsted Carbon Model in four treatments from the long‐term static fertilization experiment at Bad Lauchstädt. Four bare fallow plots were also used to test different ways of parameterizing the model. Model version 1 used Δ14C to estimate the amount of inert organic matter whereas in versions 2 and 3 a long‐term bare fallow treatment was used to estimate this amount. In version 1, C inputs were optimized from the long‐term data. In version 2, crop inputs were estimated from published functions that relate C inputs to crop yields. In version 3, C inputs (average or minimum data) were taken from actual measurements of crop and root residues. In both versions 2 and 3, rhizodeposition was included as additional input of 50% (winter wheat, spring barley) or 35% (potatoes, sugar beet) of the C input by crop and root residues. The performance of the three versions decreased in the order 3 > 2 ≫ 1. Model efficiency and root mean square error were 0.86 and 6.1 for version 3 and 0.81 and 7.0 for version 2. Overall, our results indicate the need for a long‐term treatment for calibration. Setting total C inputs as a function of crop yield performed satisfactorily. Measurements of crop and root residues gave a good representation of total C inputs when carbon from rhizodeposition was included as additional input.  相似文献   

17.
Several previous field studies in temperate regions have shown decreased soil respiration after conventional tillage compared with reduced or no‐tillage treatments. Whether this decrease is due to differences in plant residue distribution or changes in soil structure following tillage remains an open question. This study investigated (1) the effects of residue management and incorporation depth on soil respiration and (2) biological activity in different post‐tillage aggregates representing the actual size and distribution of aggregates observed in the tilled layer. The study was conducted within a long‐term tillage experiment on a clay soil (Eutric Cambisol) in Uppsala, Sweden. After 38 y, four replicate plots in two long‐term treatments (moldboard plowing (MP) and shallow tillage (ST)) were split into three subplots. These were then used for a short‐term trial in which crop residues were either removed, left on the surface or incorporated to about 6 cm depth (ST) or at 20 cm depth (MP). Soil respiration, soil temperature, and water content were monitored during a 10‐d period after tillage treatment. Respiration from aggregates of different sizes produced by ST and MP was also measured at constant water potential and temperature in the laboratory. The results showed that MP decreased short‐term soil respiration compared with ST or no tillage. Small aggregates (< 16 mm) were biologically most active, irrespective of tillage method, but due to their low proportion of total soil mass they contributed < 1.5% to total respiration from the tilled layer. Differences in respiration between tillage treatments were found to be attributable to indirect effects on soil moisture and temperature profiles and the depth distribution of crop residues, rather than to physical disturbance of the soil.  相似文献   

18.
多熟制稻田土壤有机质平衡的定位研究   总被引：30，自引：0，他引：30  
在麦稻稻三熟制下进行了连续 2 6年定位试验。结果表明 ,长期施用有机肥可以在保持高产稳产条件下使土壤有机质持续增长 ,可以显著影响有机质的增长速度 ,并培肥土壤有机质达到 60gkg- 1的高水平。在此基础上 ,构建了多熟稻田土壤的有机质数量演化数学模型 ,计算得出保持土壤有机质平衡只需厩肥 4.8thm- 2 a- 1。  相似文献   

19.
Rainfed agriculture in the semi‐arid tropical (SAT) regions of India is greatly influenced by water shortages caused by low, highly variable, and erratic rainfall. However, apart from water shortages, crop productivity in these regions is also affected by low fertility. Little effort has been devoted to diagnosing and managing the nutrient‐related problems in farmers' fields in the SAT regions of India. The ongoing integrated watershed management program by the International Crops Research Institute for the Semi‐arid Tropics and its partners provided the opportunity to diagnose the soil infertility‐related problems by soil testing, develop nutrient management protocols, and determine on‐farm crop responses to fertilization in the SAT zone of India. This article discusses examples from recent research on the diagnosis of multinutrient deficiencies and on‐farm crop responses to fertilization. Results of analyses of soil samples from farmers' fields in several districts of Andhra Pradesh, Karnataka, Tamil Nadu, Rajasthan, and Madhya Pradesh states and Junagarh district, Gujarat, showed that almost all farmers' fields had low organic carbon (C), low to moderate available phosphorus (P), and generally adequate extractable potassium (K). However, the widespread deficiencies of sulfur (S), boron (B), and zinc (Zn) were most revealing; their deficiencies varied with nutrient, district, and state. On‐farm trials conducted during three seasons (2002–2004) in three districts of Andhra Pradesh showed significant yield responses of maize, castor, groundnut, and mung bean to the applications of S, B, and Zn over farmer's input treatment, and the yield responses were larger when these nutrients were added along with nitrogen (N) and P. It is concluded that the deficiencies of nutrients such as S, B, and Zn are widespread and are holding back the potential of rainfed production systems. Clearly, nutrient deficiencies can be diagnosed by soil testing.  相似文献   

20.
Traditionally, the selective preservation of certain recalcitrant organic compounds and the formation of recalcitrant humic substances have been regarded as an important mechanism for soil organic matter (SOM) stabilization. Based on a critical overview of available methods and on results from a cooperative research program, this paper evaluates how relevant recalcitrance is for the long‐term stabilization of SOM or its fractions. Methodologically, recalcitrance is difficult to assess, since the persistence of certain SOM fractions or specific compounds may also be caused by other stabilization mechanisms, such as physical protection or chemical interactions with mineral surfaces. If only free particulate SOM obtained from density fractionation is considered, it rarely reaches ages exceeding 50 y. Older light particles have often been identified as charred plant residues or as fossil C. The degradability of the readily bioavailable dissolved or water‐extractable OM fraction is often negatively correlated with its content in aromatic compounds, which therefore has been associated with recalcitrance. But in subsoils, dissolved organic matter aromaticity and biodegradability both are very low, indicating that other factors or compounds limit its degradation. Among the investigated specific compounds, lignin, lipids, and their derivatives have mean turnover times faster or similar as that of bulk SOM. Only a small fraction of the lignin inputs seems to persist in soils and is mainly found in the fine textural size fraction (<20 µm), indicating physico‐chemical stabilization. Compound‐specific analysis of 13C : 12C ratios of SOM pyrolysis products in soils with C3‐C4 crop changes revealed no compounds with mean residence times of > 40–50 y, unless fossil C was present in substantial amounts, as at a site exposed to lignite inputs in the past. Here, turnover of pyrolysis products seemed to be much longer, even for those attributed to carbohydrates or proteins. Apparently, fossil C from lignite coal is also utilized by soil organisms, which is further evidenced by low 14C concentrations in microbial phospholipid fatty acids from this site. Also, black C from charred plant materials was susceptible to microbial degradation in a short‐term (60 d) and a long‐term (2 y) incubation experiment. This degradation was enhanced, when glucose was supplied as an easily available microbial substrate. Similarly, SOM mineralization in many soils generally increased after addition of carbohydrates, amino acids, or simple organic acids, thus indicating that stability may also be caused by substrate limitations. It is concluded that the presented results do not provide much evidence that the selective preservation of recalcitrant primary biogenic compounds is a major SOM‐stabilization mechanism. Old SOM fractions with slow turnover rates were generally only found in association with soil minerals. The only not mineral‐associated SOM components that may be persistent in soils appear to be black and fossil C.  相似文献   

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