Decline In Soil Organic Matter Research Articles

Effects of compost input and tillage intensity on soil microbial biomass and activity under Mediterranean conditions

Organic amendment and tillage reduction are two common practices to contrast soil organic matter decline, thus promoting sustainable cropping and carbon sequestration. In a horticultural land use system under Mediterranean climate, we evaluated the 9-year effects of two compost inputs (15 and 30 t ha−1 y−1, low and high input, respectively) and two tillage intensities (intensive and reduced) on soil macronutrients concentration, microbial biomass and activity. Total organic C, total N and POlsen were smaller in plots amended at low input, whilst intensive tillage decreased them at both compost inputs. These decreases in intensively tilled plots was ascribed to the disruption of soil aggregates, with consequent microbial degradation of the physically protected organic matter by oxidative processes. On the contrary, reduced tillage increased the extractable C, likely due to a higher protection of the most labile soil C fraction from the mineralization. Similarly, microbial biomass C and N increased following both doubling compost input and reducing tillage intensity, with a greater effect by the first factor. The higher values of cumulative 10-day basal and 20-h glucose-induced respiration, and metabolic quotient in intensively tilled plots suggested that high tillage favoured soil aggregate disruption and C accessibility. This was also confirmed by higher values of dehydrogenase activity/total organic C in those plots. Intensive tillage caused a higher soil aeration and organic substrates accessibility to microflora, thus undoing the fertility benefits provided by the high compost input. However, also a low compost input coupled to reduced tillage seemed to accomplish soil sustainability needs.

The need for harmonizing methodologies for assessing soil threats in Europe

AbstractCentral to the EU thematic strategy for soil protection is that areas affected by soil degradation through erosion, soil organic matter (SOM) decline, compaction, salinization and landslides should be identified in a clear and consistent way. However, the current methodologies to achieve this often differ and this can result in different perceptions of risks amongst EU Member States. The aims of this paper are to: (i) assess the current status of assessment methodologies in Europe (EU27) associated with erosion, SOM decline, compaction, salinization and landslides and (ii) discuss the issues associated with harmonization of these methodologies throughout the EU27. The need for harmonization is assessed using the relative share of common elements between different methodologies. The results demonstrate that the need for harmonization in methodology is greatest for erosion and compaction and least for SOM decline and landslides. However, many of the methodologies which were investigated are still incomplete and there are significant differences in terms of: (i) understanding the threats, (ii) methods of data collection, (iii) processing and interpretation and (iv) risk perception. We propose two options for the harmonized assessment of soil threats: (i) a two‐tiered approach based on data availability and spatial scale and (ii) a combination of standardization and harmonization for each assessment methodology. Future assessments should focus on the advantages and disadvantages of these options as the current situation will result in endless discussions on differences and the merits of particular methodologies instead of taking appropriate measures to reduce or eliminate the actual threats.

Experiences and Research Perspectives on Sustainable Development of Rice-Wheat Cropping Systems in the Chengdu Plain, China

The rice and wheat cropping pattern is one of the main cropping systems in the world. A large number of research results showed that successive cropping of rice and wheat resulted in a series of problems such as hindering nutrition absorption, gradual degeneration of soil fertility, decline of soil organic matter, and increased incidence of diseases and pests. In China, especially in the Chengdu plain where rice-wheat cropping system is practiced, productivity and soil fertility was enhanced and sustained. This paper reviews the relevant data and experiences on rice-wheat cropping in the Chengdu Plain from 1977 to 2006. The principal sustainable strategies used for rice-wheat cropping systems in Chengdu Plain included: 1) creating a favorable environment and viable rotations; 2) balanced fertilization for maintenance of sustainable soil productivity; 3) improvement of crop management for higher efficiency; and 4) use the newest cultivars and cultivation techniques to upgrade the production level. Future research is also discussed in the paper as: 1) the constant topic: a highly productive and efficient rice-wheat cropping system for sustainable growth; 2) the future trend: simplified cultivation techniques for the rice-wheat cropping system; 3) the foundation: basic research for continuous innovation needed for intensive cropping. It is concluded that in the rice-wheat cropping system, a scientific and reasonable tillage/cultivation method can not only avoid the degradation of soil productivity, but also maintain sustainable growth in the long run.

Soil‐carbon turnover under different crop management: Evaluation of RothC‐model predictions under Pannonian climate conditions

AbstractDespite 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.

Trade-offs between the short- and long-term effects of residue quality on soil C and N dynamics

The decline of soil organic matter (SOM) and its associated fertility is one of the most important constraints to enhanced crop productivity in sub-Saharan Africa. Integrated soil fertility management recognizes the potential benefits of the combined use of organic residue and mineral fertilizer inputs for improved crop yield and SOM build up. However, these benefits may be controlled by residue quality. We examined the short- to long-term C and N dynamics following application of different quality residues with and without N fertilizer in a series of experiments comprising different timescales of measurement in a Kenyan Humic Nitisol. The combined results of these studies indicate that residue quality and fertilizer additions alter short-term C and N mineralization. Combining low quality residue and fertilizer inputs immobilized a greater amount of fertilizer-N than high quality residue. Under field conditions, this reduction in available N induced by the combination of low quality residue and fertilizer reduced environmental N losses and created a positive interactive effect on crop N uptake. While input management manipulated short-term nutrient dynamics, it did not influence long-term SOM stabilization. The input of residue, regardless of quality, contributed to long-term soil fertility improvement. In conclusion, organic residue quality can be manipulated to optimize short-term nutrient dynamics while still conferring the same benefits to long-term SOM contents.

Measuring soil organic carbon in croplands at regional scale using airborne imaging spectroscopy

Conventional sampling techniques are often too expensive and time consuming to meet the amount of data required in soil monitoring or modelling studies. The emergence of portable and flexible spectrometers could provide the large amount of spatial data needed. In particular, the ability of airborne imaging spectroscopy to cover large surfaces in a single campaign and to study the spatial distribution of soil properties with a high spatial resolution represents an opportunity for improving the monitoring of soil characteristics and soil threats such as the decline of soil organic matter in the topsoil. However, airborne imaging spectroscopy has been generally applied over small areas with homogeneous soil types and surface conditions. Here, five hyperspectral images acquired with the AHS-160 sensor (430 nm–2540 nm) were analysed with the objective to map soil organic carbon (SOC) at a regional scale. The study area, covering a surface of ∼ 420 km 2 and located in Luxembourg, is characterized by different soil types and a high variation in SOC contents. Reflectance data were related to surface SOC contents of bare croplands by means of 3 different multivariate calibration techniques: partial least square regression (PLSR), penalized-spline signal regression (PSR) and support vector machine regression (SVMR). The performance of these statistical tools was tested under different combinations of calibration/validation sets (global and local calibrations stratified according to agro-geological zones, soil type and image number). Under global calibration, the Root Mean Square Error in the Predictions reached 5.3–6.2 g C kg − 1 . Under local calibrations, this error was reduced by a factor up to 1.9. SOC maps of bare agricultural fields were produced using the best calibration model. Two map excerpts were shown, which display intra- and inter-field variability of SOC contents possibly related to topography and land management.

Soil organic C stabilization and thresholds in C saturation

When building soil organic matter (SOM) contents in agricultural production systems, stabilization of both pre-existing as well as added C is important. A laboratory mineralization experiment was conducted over 374 days to evaluate the effect of pre-existing SOM on soil C mineralization after addition of organic matter (OM) using sugar cane. The SOM gradient used here stretched from 21 to 106 g C kg −1 soil and was a result of different periods of continuous cultivation of 5, 20, 35 and 105 years in comparison to a forest soil. The rate of organic C mineralization was found to be dependent on the status of pre-existing soil organic C (SOC). Highly degraded soil which had been under continuous cultivation for 35 years and more showed the highest rate of C mineralization per unit SOC (117.9 mg C g −1 C) while forest soil had the lowest amount of C mineralized per unit SOC (73.5 mg C g −1 C). Forest soil had the highest amount of increased C mineralization as a result of organic matter (OM) additions (8.0 mg C g −1 soil) followed by the highly degraded soil that had been under cultivation for 105 years (5.5 mg C g −1 soil). Additional mineralized C as a function of time after forest conversion declined progressively within the first 20 years of continuous soil use. Soil which had been under continuous cultivation for 20 years had the lowest amount of additional mineralized C (4.0 mg C g −1 soil). SOM stabilization efficiency in the studied soils appears to be highest with intermediate cultivation history of about 20 years. These soils that have been recently converted to cultivation also appear to have a greater ability to stabilize added OM than the most degraded soils investigated in this study. It is thus advisable to provide intervention strategies to reverse SOM decline for farming communities at an intermediate stage before the soils are highly depleted of SOC.

Organic Matter and Water Stability of Field Aggregates Affected by Tillage in South Dakota

Tillage has been associated with soil organic matter (SOM) decline. A case study of two adjacent farms was conducted in eastern South Dakota. One farm used no‐till (NT) and the other used chisel tillage (CT). We hypothesized that soil under NT, compared with tillage, would have both greater quantity and greater quality of SOM and that this improved SOM condition would result in increased water stable aggregation (WSA). A rotary sieve was used to sort dry field aggregates into six size groups: <0.4, 0.4 to 0.8, 0.8 to 2.0, 2.0 to 6.0, 6.0 to 19.0, and >19 mm. Water stable aggregation, soil organic C (SOC), N, glomalin, and basidiomycete fungi were measured. Fine particulate soil organic matter (fPOM, 0.5–0.053 mm) and coarse particulate organic matter (2.0–0.5 mm) were isolated by sieving. Quantitative solid‐state 13C nuclear magnetic resonance was used to determine C type in humic acid, humin, and whole soil. The fPOM/SOM ratio was greatest in <0.4‐mm aggregates and 24% greater in NT than CT. Soil organic C was greatest in 0.8‐ to 2.0‐mm aggregates and 11% greater in NT than CT. Average WSA was 63% greater under NT than under CT. Aggregate wettability was less under NT than CT. Slower water uptake under NT might be attributed to a greater abundance of wax‐type C under NT than under CT. We conclude that NT, compared with CT, resulted in better SOM quality during the course of 10 yr. Improved SOM quality was related to improved WSA.

CQESTR Simulation of Management Practice Effects on Long‐Term Soil Organic Carbon

Management of soil organic matter (SOM) is important for soil productivity and responsible utilization of crop residues for additional uses. CQESTR, pronounced “sequester,” a contraction of “C sequestration” (meaning C storage), is a C balance model that relates organic residue additions, crop management, and soil tillage to SOM accretion or loss. Our objective was to simulate SOM changes in agricultural soils under a range of climate and management systems using the CQESTR model. Four long‐term experiments (Champaign, IL, >100 yr; Columbia, MO, >100 yr; Lincoln, NE, 20 yr; Sidney, NE, 20 yr) in the United States under various crop rotations, tillage practices, organic amendments, and crop residue removal treatments were selected for their documented history of the long‐term effects of management practice on SOM dynamics. CQESTR successfully simulated a substantial decline in SOM with 50 yr of crop residue removal under various rotations at Columbia and Champaign. The increase in SOM following addition of manure was simulated well; however, the model underestimated SOM for a fertilized treatment at Columbia. Predicted and observed values from the four sites were significantly related (r2 = 0.94, n = 113, P < 0.001), with slope not significantly different from 1. Given the high correlation of simulated and observed SOM changes, CQESTR can be used as a reliable tool to predict SOM changes from management practices and offers the potential for estimating soil C storage required for C credits. It can also be an important tool to estimate the impacts of crop residue removal for bioenergy production on SOM level and soil production capacity.

The Magruder Plots: Untangling the Puzzle

Long‐term experiments play a vital role in revealing dynamic soil and weather processes that directly influence sustainable crop production and ecosystem health. The objective of this review paper is to present one of the oldest long‐term continuous winter wheat (Triticum aestivum L.) experiments, the Magruder Plots, and their contribution to the scientific community regarding questions of yield response to amendments, yield stability, percentage organic matter (OM) lost over time, soil nutrient status, microbial activity, weed population, and information on the economic return from winter wheat production. Alexander C. Magruder initiated the experiment in 1892 and is in progress to date. The original plot was started to evaluate wheat production on native prairie soils without fertilization. After 6 yr the principal investigator split the initial plot into two and fertilized one half with cattle manure. The experiment was then modified to include 10 treatments in 1930 by Dr. Horace J. Harper to answer several soil fertility related questions. Since 1947, six treatments have remained intact that evaluate simple combinations of manure, and inorganic N, P, K, and lime. Following 114 yr of continuous winter wheat production under conventional tillage, the check plot that has never received any fertilizer addition continues to produce wheat grain yields of >1 Mg ha−1. Despite the decline in soil organic matter from 4 to 1% during this time period, wheat grain yields continue to show slight increases with time, likely due to improved genetics. While continuous wheat without rotation is not recommended, this 114‐yr study documents the feasibility.

EU strategies and policies on soil and waste management to offset greenhouse gas emissions

Climate change has become an important political priority in the environmental field, and beyond. To revert the increase in the Earth's temperature, developed country parties to the Kyoto Protocol committed to limit their greenhouse gas emissions. The 15 Member States that made up the European Community in 1997 have a combined reduction target of 8% in CO2-equivalent emissions in the period 2008-2012 compared to 1990. The role of soil, both as a source and a sink for carbon, is particularly important. How can soil organic matter be maintained or increased? There is no single answer, and a broad range of options need to be explored. Among the different measures proposed, the promotion of organic input on arable land (crop residues, cover crops, farm yard manure, compost, sewage sludge) has been mentioned. The challenge is to ensure that organic wastes of good quality are used to increase soil organic matter in carbon depleted soils and that appropriate monitoring is established. On the waste management front, the European Commission intends to produce guidance for Member States on the management of biowaste that will take into account all related environmental issues, including soil aspects. As for monitoring, the European Commission has put forward legislation according to which Member States would have to identify the areas at risk of soil organic matter decline in their national territory. Such legislation should be regarded as a major step forward for Europe, as it would ensure a high level of soil protection across the Community. This development will have the potential to enable the kind of estimation, measurement or modelling of crop or grazing land management needed for accounting under Article 3.4 of the Kyoto Protocol.

The Magruder Plots: Untangling the Puzzle

Long‐term experiments play a vital role in revealing dynamic soil and weather processes that directly influence sustainable crop production and ecosystem health. The objective of this review paper is to present one of the oldest long‐term continuous winter wheat (Triticum aestivum L.) experiments, the Magruder Plots, and their contribution to the scientific community regarding questions of yield response to amendments, yield stability, percentage organic matter (OM) lost over time, soil nutrient status, microbial activity, weed population, and information on the economic return from winter wheat production. Alexander C. Magruder initiated the experiment in 1892 and is in progress to date. The original plot was started to evaluate wheat production on native prairie soils without fertilization. After 6 yr the principal investigator split the initial plot into two and fertilized one half with cattle manure. The experiment was then modified to include 10 treatments in 1930 by Dr. Horace J. Harper to answer several soil fertility related questions. Since 1947, six treatments have remained intact that evaluate simple combinations of manure, and inorganic N, P, K, and lime. Following 114 yr of continuous winter wheat production under conventional tillage, the check plot that has never received any fertilizer addition continues to produce wheat grain yields of >1 Mg ha−1. Despite the decline in soil organic matter from 4 to 1% during this time period, wheat grain yields continue to show slight increases with time, likely due to improved genetics. While continuous wheat without rotation is not recommended, this 114‐yr study documents the feasibility.

Whole-System Integration and Modeling Essential to Agricultural Science and Technology for the 21st Century

In the 21st century, agricultural research has more difficult and complex problems to solve. The continued increase in population in the developing countries requires continued increases in agricultural production. However, the increased use of fertilizers, pesticides, and water required for the new higher yielding crop varieties has been causing environmental problems. Excessive leaching and runoff of agricultural chemicals are seriously affecting the quality of both the groundwater and surface waters. Increase in soil salinity, decline in soil organic matter, and increase in soil erosion remain the major problems in intensively farmed areas. Even the air quality is being affected. At the same time, market-based global competition is challenging the economic viability of traditional agricultural systems. Global climate change will pose additional challenges. The solution or mitigation of these changing and multiple problems will require continual improvement or changes in management and selection of dynamic cropping systems using a whole-system approach. Therefore, synthesis and quantification of disciplinary knowledge at the whole-system level is essential to meeting these challenges. The process-based models of agricultural systems provide such a synthesis and quantification for evaluating the effects of varying management practices, crops, soils, water, and climate on both the production and the environment. These system models will greatly enhance the efficiency of field research for developing sustainable agricultural systems, serve as guides for planning and management, and help transfer new technologies to various conditions of developing countries. Current state of the system models and their applications for these purposes are reviewed, and advancements needed in models to improve and extend these applications are presented.

Soil fertility differences across a land-use intensification gradient in the highlands of Chiapas, Mexico

In the highlands of Chiapas, southern Mexico, soil texture and soil chemical properties were measured in 70 agricultural fields covering a range of slope positions and managements. Fields represented four corn cropping systems: long fallow, short fallow, pasture–cultivation rotation, and annual continuous cultivation, in addition to fallow at rest (forest, shrubland, and pastures). Fields were located in four slope positions (upper, middle, and lower slopes, and doline floor) in a karst landscape developed on limestone with additions of acid volcanic ashes. Distribution of clays and sands were related to the toposequence and the percentage of clay fraction increased from upper slope to doline floor. Sand presented a reverse pattern. Some soil chemical properties also vary in a characteristic way along the toposequence. Exchangeable Ca2+ and Mg2+ effective cation exchange capacity (ECEC) and pH were higher in the doline floor than in the other slope positions. Soil organic matter and total N contents were 30.4 and 35.2% higher under long fallow than under annual continuous cultivation. Soil Olsen P was greater under cultivation than under fallow (irrespective of the cropping system), with the highest values under annual continuous cultivation (16.2±8.3 mg kg−1) and the lowest in the forest (5.3±2.5 mg kg−1). Exchangeable K+ was 74 and 51% higher in cultivated plots of the long and the short fallow than under forest and shrubland, respectively. Exchangeable Ca2+ and Mg2+ and ECEC did not vary significantly among the cropping systems. Inputs of basic cations through burning of tree and shrub vegetation increased the soil pH. These results indicate that land use intensification is leading to a decline in soil organic matter and total N, whereas Olsen P increased with intensification due to the continuous application of P fertilizers and sheep manure as soil conditioners in intensively cultivated fields.

Strengthening optimal food chain element transport by minimizing soil degradation recommendations for soil threats identification on different scales in the European union

Introduction The functional relationships between the elements of the food chain are strongly affected by the degradation of soil. It was realized by the European Commission when it launched a new policy to maintain the optimum soil functions through minimizing soil degradation. In the context of communication "Towards a Thematic Strategy for Soil Protection" by the European Commission, major threats have been identified representing the most important hazards endangering the functioning of soils (EC 2002, Varallyay 2005), including its ability to enhance plant productivity. According to current proposals, that would aim to strike the right balance between EU action and subsidiarity, Member States of the EU shall identify the location and boundaries of land areas in risk of degradation, for each major area-dependent threat to soils. Five major threats have been identified, which are soil and area specific in their appearance: (I) soil organic matter decline (2) erosion (3) compaction (4) salinisation/sodification and (5) landslides. Soil sealing and contamination as well represent major risks for soil functions, however, the probability of occurrence of these threats are mainly independent from soil and land characteristics (Birkis et al. 2005; JRC-IES 2005; Ling et al. 2004). With the collaboration of the Joint Research Centre (JRC) and the European Soil Bureau Network (ESBN), the Soil Information Working Group (SIWG) has been established to prepare a proposal with identification of common criteria to delineate risk areas on different scales (JRC-IES 2005). Present paper summarizes the main conclusions drawn by the SIWG and attempts to estimate the applicability of the approach.

Soils as sources and sinks of greenhouse gases

Abstract Soils annually emit between 6.8 and 7.9 Gt CO 2 equivalents, mainly as CH 4 from intact peatlands and from rice agriculture; as N 2 O from unmanaged and managed soils; and as CO 2 from land-use change. Methane emissions attributable to other wetlands add another 1.6–3.8 Gt CO 2 equivalents. From a global standpoint, N 2 O from unmanaged soils and CH 4 from peatlands and other wetlands make soils naturally net greenhouse gas emitters. In addition, the storage of carbon in soils and the fluxes of CH 4 and N 2 O have been changed by anthropogenic effects towards emission rates 52 to 72% above those under natural conditions before the dawn of intensive agriculture and land-use change. Land-use changes on mineral soils induced most of the recorded losses of soil organic matter (SOM), but there is evidence that proper agricultural management of soil resources is able to recover some of these losses and to maintain soil functions. However, the discrepancy between so-called ‘sequestration potentials’ and the measures already adopted is amazingly large. Globally, only about 5% of the cropped areas is managed according to practices such as no tillage or organic farming. The contribution of soil loss by erosion, desertification and sealing to global oxidative SOM losses is uncertain; however, in the case of soil erosion, it is considered to be a major factor in global SOM decline. Mitigation options calculated for SOM restoration, reduced CH 4 and N 2 O emissions are able to alleviate mean annual emissions by 1.2 to 2.9 Gt CO 2 equivalents, mainly as a result of carbon sequestration, which is the most efficient measure for the next few decades. In the longer term, however, the large potential for reducing CH 4 and N 2 O emissions outweigh the finite capacity of soils to recover C. Integrated assessment of net greenhouse-gas fluxes is key for evaluating management practices aimed at reducing overall emissions. From the viewpoint of climate change and taking into consideration the mean fluxes of CO 2 , CH 4 and N 2 O, peatland protection is more favourable than peatland cultivation in the long term. The most important gaps in our understanding appear to be with regard to estimating fluxes along with soil erosion and desertification processes, in the extent of peatland cultivation; the role of black carbon formation, natural ‘background’ sequestration rates of undisturbed soils; and the net response of soils, particularly in cold regions, to global warming. With regard to the societal perception of soil contributing to the global cycling of greenhouse gases, it is important to emphasize that significant proportions of the emissions are inevitably linked to intensive agriculture.

Soil organic matter map of Hungary derived from digital elevation model and satellite data

One of the major stresses on the soil functions is the decline of soil organic matter (SOM) content. Soil Information and Monitoring Systems were setup to survey the recent situation and estimate the rate and trend of potential changes in different soil properties and components including SOM. These Monitoring systems are profile or point based networks with regular sampling periods, which can provide limited, often insignificant percentage of the country surface. The collected data need to be extrapolated to create continuous coverage of the land area of interest.

Cultivation and Soil Organic Matter Management in Low Input Cereal Production following the Ploughing out of Grass Leys

Nitrogen fertility of low input cereal systems following ploughing out of grass leys is investigated using the soil nitrogen dynamics model SOILN with its linked cereal growth model, supported by a set of experimental data for spring and winter barley cropping. Soil organic matter (OM) plays an important part in transfer of fertility from the fertility-building ley phase to the fertility exploitation arable phase of ley-arable rotations. One aspect investigated is a possible role of ‘protected organic matter’, a component of soil OM which generally mineralises at a slow rate, but which becomes ‘unprotected’ so it mineralises at a somewhat faster rate for a limited period following disturbance of the soil by ploughing. Measurements of CO2 emissions in the laboratory and field support the concept of protected OM. In simulations with the SOILN model, this is represented by a temporary increase in the value of the humus decomposition rate constant for a few weeks following ploughing. The assumption of raised humus decomposition rates after ploughing makes some improvements to fits of simulations with the linked models to measured grain and straw yields and N offtakes, as well as giving a more realistic decline in soil OM over successive years of cereal cropping. Predictive simulations demonstrate how, in the absence of mineral N fertiliser, cereal crop yields decline over the years following ploughing out of leys, but yields can be maintained by making applications of organic manure or slurry.

Soil organic matter, surface crusting and erosion in Sahelian farming systems based on manuring or fallowing

The cultivated soils of the Sahel are sandy, very poor in organic matter, and are prone to surface crusting and erosion. Farmers sustain pearl millet production through permanent cultivation with manure input or long-term fallowing. Due to population increase fallows are reduced bringing on low yields. This on-farm study (Banizoumbou, semi-arid Niger) examines the impact of clearing and weeding on soil surface processes, the decline in soil organic matter under prolonged cultivation, and whether manure inputs are sufficient to sustain millet production. Short-term effects were examined in a 3-year experiment with dung application (5 Mg ha−1) and weeding frequency (no, two and four weedings). Long-term effects were studied a 4-year experiment comparing three farming systems: (i) permanent cultivation with manure; (ii) cultivation after long fallows >15 years; (iii) cultivation after short fallows 3–5 years. Due to the difference in scale, different processes of erosion were studied, saltation and creep in the first experiment, suspension in the second. Dung deposits provided mechanical protection of the soil surface by reducing crusting and by trapping aeolian sand. A very low cover of dung, 0.5–5%, is enough to protect the soil effectively by forming barriers against creep and saltation. Suspension occurs during tillage. Manual cultivation, while disrupting aggregates and surface crusts, enhances wind erosion and this leads to loss of clay and silt from the top soil. Changing from long to short fallow periods and even to permanent cultivation, constitutes a trend towards more intensive land use and this, eventually, leads to extremely sandy top soils (from 890 up to 934 g kg−1) and coincidences with a soil surface becoming less crusted (from 49% of field surface affected down to 7%). Manure input cannot prevent the erosion of fine earth which seems to be an irreversible feature of long-term cultivation. Dung inputs, 0.5–1 Mg ha−1 per year, are insufficient to increase substantially millet grain yield (350 kg ha−1 in manured; 300 kg ha−1 in long fallow fields), or elevated soil organic matter (2.9 g kg−1 soil, in manured fields; 4.0 g kg−1 in long fallow fields, 0–20 cm). Yet grain yield remains stable under permanent cropping, while fields without manure need fallowing for long periods to restore fertility. Under short fallows without dung input soil organic matter drops to 2.4 g kg−1, and grain yields to 125 kg ha−1.

The technology adoption behavior of women farmers: The case of alley farming in Nigeria

The indigenous system of crop production in Nigeria, the bush fallow farming system, which is known for its stability and biological efficiency, can no longer be operated effectively, due to a shortage of land. In order to increase farm productivity, researchers have devised alley farming, a low-input farming system which sustains crop and livestock production, can reduce competition from weeds, and conserves soil by reducing soil physico-chemical degradation and the decline of soil organic matter. The mobilization of women to adopt agricultural innovations is an important topic in development studies. Due to the important role of Nigerian women farmers in crop and livestock production, they are encouraged to adopt alley farming. Contrary to some of the literature, which claims that women are slow innovation adopters, this study argues that women farmers easily adopt innovations that can enhance their economic status. The paper argues that the characteristics of alley farming influence women farmers‘ adoption or rejection of the farming system. It was observed that the land tenure system is not an inflexible constraint on alley farming adoption. It is argued that low participation of women in agricultural innovation adoption is caused by lack of information about the advantages of the innovations, because meetings are fixed at times when women are not able to attend. This paper points out that the adoption of alley farming has increased the agricultural production and the quality of life of women farmer adopters.