Factors influencing the utilization of cattle and chicken manure for soil fertility management by emergent farmers in the moist Midlands of KwaZulu-Natal Province, South Africa

The study established the factors that influence the use of cattle andchicken manure for managing soil fertility by surveying a random sample of 224farm households in the Midlands of KwaZulu-Natal province, South Africa. Themajority (87%) of the respondents are farming on communal land with an averagefarm size of 2.9 ha. Sixty-three% of the farmers in the sampleusedmanure to manage soil fertility in their fields. Despite the fact that chickenmanure was available in large quanties in the area, 54% of manure usedwas from cattle while chicken manure was used by 39% of the sample.Manure was readily available to 73% of the respondent farmers and it wasobtained mostly from commercial and semi-commercial livestock production unitswithin the area. Most of the manure was applied on land planted to high valuecrops such as maize, potatoes and vegetables. The common method of applyingmanure was by a spreader. The major factors that positively influencedthe farmers' decision to use manure were availability of manure, herd size,farmers' experience in farming and the availability of extension services.Both land ownership and attendance of training did not seem to affect thefarmers' decision to use manure. Farm size was the factor that was foundtonegatively affect manure utilization. Other important considerations includedlabor and transport requirements for handling manure, lack of technicalinformation on the fertilizer value and management of manure, increased growthof weeds and bad smell. Some suggestions are made on strategies that couldimprove the efficiency of utilization of manure for soil fertility managementinthis agroecosystem.     

Utilization and management practices of animal manure for replenishing soil fertility among smallscale crop farmers in semi-arid farming districts of the North West Province,South Africa

Poor soil fertility is one of the most limiting biophysical factors to agricultural production among smallscale farmers in much of the sub-Saharan Africa, especially the semi-arid areas. In this study, a survey of 200 randomly selected farming households across four districts (Mafikeng, Ditsobotla, Ganyesa and Taung) located in a semi-arid environment of the North West Province in South Africa was conducted to establish the utilisation and management of animal manure for managing soil fertility. The results showed that 66% of the farmers across the districts used animal manure on their crops. The types of manure used were in the order cattle > sheep = goat > chicken. Cattle manure was readily available from farmers’ own kraal or neighbours. Despite its availability and advantages, chicken manure was seldom used. The rates of manure application were generally low (mean 2.5 tha⁻¹) although most farmers (71%) applied it annually. In the majority of cases, manure would be applied to about half (57.5%) of the cropped land every year (average farm size was 5.3 hectares). The manure was mostly broadcasted (76%) on the surface before being ploughed under followed by dollop (53%). The quality of most of the manure resources was relatively poor as it had low N and P but high soil content (mean 22.7%). The study found that farmers have developed local knowledge with regards to criteria for defining manure quality. The criterion, which used physical characteristics such as colour, moisture content and presence of moulds in the manure, was quite consistent across the study districts and points to the possibility of the indigenous knowledge being interfaced with scientific knowledge. The factors which positively influenced farmers’ decision to use manure were herd sizes, farming experience, training and availability of manure, extension services and labour. On the other hand, farm sizes negatively affected manure use. It was observed that housing, feeding, storage and handling practices of manure resources was not optimum in most of the study districts and this contributed to loss of nutrients and quality. It is recommended that improved strategies of manure production and handling be adopted by farmers in order to maximise the quality and efficiency of manure utilization. The potential that exists in using chicken manure to supply crop nutrients needs to be explored.     

Farmers' perceptions and attitudes towards introduced soil-fertility enhancing technologies in western Africa

Soil fertility enhancing technologies (SFETs) have been promoted in the West African Semi-Arid Tropics (WASAT) for many years with limited success. Using a qualitative approach of focus group discussions, long, open-ended interviews and observations from field visits, this paper explores with farmers their beliefs and rationales behind the adoption or non-adoption of SFETs. Farmers are knowledgeable about, and practise SFETs of rock phosphate application, crop residue and farm yard manure, chemical fertilizer and crop rotation to combat soil fertility decline. Their attitudes to and rationales behind adoption decisions are influenced by the availability and use policies of land and labour resources, food security concerns, perceived profitability, contribution to sustainability and access to information. Some of the factors are beyond farmers' control and require a broad and integrated effort from research, extension and government to promote the use of the SFETs in the region.     

Temporal and spatial trends in soil organic carbon stocks following maize cultivation in semi-arid Tanzania,East Africa

Conversion of native ecosystems to agro-ecosystems influences the amount, quality and turnover of soil organic carbon (SOC). As most agro-ecosystems are not in a steady state in terms of the content of SOC, the time scale and feedback mechanisms of changes in SOC are highly relevant for predicting future soil fertility and potential rates of soil carbon losses or sequestration. This paper focuses on changes in land use linked to measured changes in the distribution of total stocks of SOC and the δ¹³C signature in the upper 0.5 m of cultivated soils in the semi-arid parts of Tanzania. Based on documented land use changes since 1950s using remote sensing data, 12 sampling sites along two transects were selected to represent semi-natural/natural savannah and maize fields cultivated for up to five decades. Comparisons between sites representing a chronosequence of well-drained soils showed that soils cultivated the last 50 years have in average less than 50% SOC compared to soils which have never been cultivated. Variations between sites were significant and a reduction in SOC could not be established at sites near present or former villages which have received substantial manure despite a long cultivation history or along a chronosequence representing wetter and more fine-grained soils. Spatial variations in land use changes were parameterized based on remote sensing data and successfully validated against sampling sites. Site-specific rates of soil element loss following cultivation were extrapolated to the study area and uncertainties related to scaling up were discussed.     

Factors affecting the use of fertilizers and manure by smallholders: the case of Vihiga,western Kenya

Sub-Saharan Africa faces huge food supply challenges due to increasing human population, limited opportunities to increase arable land, and declining yields associated with continuously declining soil fertility. To cater for their food requirements, smallholders use only modest levels of inorganic fertilizers and rely to a large extent on manure, which is generally of low quality. To explore factors influencing fertilizer and manure use at the farm level, 253 farm households in Vihiga district of western Kenya were sampled. A pair of Tobit models was used to relate amounts of manure and fertilizer used to household variables. The results indicate that the use of both manure and fertilizer reciprocally influence each other and are strongly influenced by household factors, and also imply that manure and fertilizer uses are endogenous. Policy changes are required to (1) reduce the burden on farming alone in rural areas; (2) promote the use of higher-cost, higher-value inputs such as fertilizers; (3) improve access to input and output markets; and (4) encourage farmer education so as to promote sustainable soil fertility management. Improved understanding of the biophysical and socioeconomic environment of smallholder systems can help target sustainable soil fertility interventions more appropriately.

The role of fertilizers in sustaining agriculture in sub-Saharan Africa

African farmers have relied traditionally on fallowing for up to 15 years to restore soil fertility. Leaving land unproductive for such periods is a luxury many regions cannot afford, given the contemporary decline in per capita food production (1%/year). Thus, alternative soil fertility maintenance measures such as agroforestry, novel intercropping systems, residue conservation, the use of manure, soil amendments, and fertilizer have recently been given greater emphasis. The Food and Agriculture Organization (FAO) estimates that 75% of the increase in regional food production must come from intensive production. However, fertilizer use in sub-Saharan Africa is only one tenth of the world average. The small size of fertilizer markets in most countries is an important contributing factor in relatively high farm-gate prices and low fertilizer use. There is significant scope for improving the efficiency of fertilizer procurement and distribution in the region. Most countries can substantially reduce farm-gate prices by changing to higher analysis formulas, relaxing specifications, importing in bulk and bagging locally, and improving systems of distribution. Various options of fertilizer production are discussed in this context. Intensification in areas where environmental constraints are limited and surplus production can be marketed may alleviate the demographic pressures to cultivate marginal land where increased land and labor productivity is unlikely. Although substantial effort should be made to research sustainable farming system options for marginal lands, efforts in the more resilient environments should concentrate on increased crop production, using inputs where feasible. Provisions should be made for adequate support in the infrastructural, institutional, and policy spheres to transform these regions into granaries.     

Composting of Disposal Organic Wastes: Resource Recovery for Agricultural Sustainability

One of the major problems of agricultural soils in the tropical regions of the Pacific is the low organic matter content. Because of the hot and humid environment, the soil organic matter (SOM) is minimal due to rapid decomposition. Composted organic material is being applied on agricultural fields as an amendment to provide nutrients and enhance the organic matter content for improving the physical and chemical properties of the cultivated soils. In addition land application of composted material as a fertilizer source effectively disposes of wastes that otherwise are buried in landfills. In our soil program at the University of Guam, we are evaluating the use of organic material as an alternative to synthetic fertilizers. Its goal is to develop management strategies and use available resources for improving crop production while conserving resources and preserving environmental quality. Our case study project is designed to improve soil fertility status by using composted organic wastes and assessing how the nitrogen and other essential nutrients contribute to long-term soil fertility and crop productivity without application of synthetic fertilizers. In our pilot project, compost is produced from wood chips, grinded typhoon debris mixed with animal manure, fish feed, shredded paper and other organic wastes. Mature compost is then applied on the field at the rates of 0, 5, 10 and 20 t/ha as a soil amendment on the eroded cobbly soils of southern Guam. Corn is planted and monitored for growth performance and yield. The effect of land application of composted material on the SOM content and overall soil quality indices are being evaluated in this pilot study.     

A critical analysis of challenges and opportunities for soil fertility restoration in Sudano-Sahelian West Africa

Since the 1970s, research throughout West Africa showed that low soil organic matter and limited availability of plant nutrients, in particular phosphorus and nitrogen, are major bottlenecks to agricultural productivity, which is further hampered by substantial topsoil losses through wind and water erosion. A few widely recognized publications pointing to massive nutrient mining of the existing crop–livestock production systems triggered numerous studies on a wide array of management strategies and policies suited to improve soil fertility. Throughout Sudano-Sahelian West Africa, the application of crop residue mulch, animal manure, rockphosphates and soluble mineral fertilizers have been shown to enhance crop yields, whereby yield increases varied with the agro-ecological setting and the rates of amendments applied. In more humid areas of Western Africa, the intercropping of cereals with herbaceous or ligneous leguminous species, the installation of fodder banks for increased livestock and manure production, and composting of organic material also proved beneficial to crop production. However, there is evidence that the low adoption of improved management strategies and the lack of long-term investments in soil fertility can be ascribed to low product prices for agricultural commodities, immediate cash needs, risk aversion and labour shortage of small-scale farmers across the region. The wealth of knowledge gathered during several decades of on-station and on-farm experimentation calls for an integration of these data into a database to serve as input variables for models geared towards ex-ante assessment of the suitability of technologies and policies at the scale of farms, communities and regions. Several modelling approaches exist that can be exploited in this sense. Yet, they have to be improved in their ability to account for agro-ecological and socio-economic differences at various geographical scales and for residual effects of management options, thereby allowing scenario analysis and guiding further fundamental and participatory research, extension and political counselling.     

Intensity cultivation induced effects on soil organic carbon dynamic in the western cotton area of Burkina Faso

The soil organic carbon (SOC) dynamic is a key element of soil fertility in savannah ecosystems that form the key agricultural lands in sub-Saharan Africa. In the western part of Burkina Faso, the land use is mostly linked to cotton-based cropping systems. Use of mechanization, pesticides, and herbicides has induced modifications of the traditional shifting cultivation and increased the need for sustainable soil fertility management. The SOC dynamic was assessed based on a large typology of land cultivation intensity at Bondoukui. Thus, 102 farm plots were sampled at a soil depth of 0–15 cm, considering field–fallow successions, the cultivation phase duration, tillage intensity, and soil texture. Physical fractionation of SOC was carried out by separating the following particle size classes: 2,000–200, 200–50, 50–20, and 0–20 μm. The results exhibited an increase in SOC stock, and a lower depletion rate with increase in clay content. After a long-term fallow period, the land cultivation led to an annual loss of 31.5 g m⁻² (2%) of its organic carbon during the first 20 years. The different fractions of SOC content were affected by this depletion depending on cultivation intensity. The coarse SOC fraction (2,000–200 μm) was the most depleted. The ploughing-in of organic matter (manure, crop residues) and the low frequency of the tillage system produced low soil carbon loss compared with annual ploughing. Human-induced disturbances (wildfire, overgrazing, fuel wood collection, decreasing fallow duration, increasing crop duration) in savannah land did not permit the SOC levels to reach those of the shifting cultivation system.     

Farm typologies,soil fertility variability and nutrient management in smallholder farming in Sub-Saharan Africa

Farm typologies are a useful tool to assist in unpacking and understanding the wide diversity among smallholder farms to improve targeting of crop production intensification strategies. Sustainable crop production intensification will require the development of an array of nutrient management strategies tailored to farm-specific conditions, rather than blanket recommendations across diverse farms. This study reviewed key literature on smallholder farm typologies focusing on three countries (Kenya, Malawi and Zimbabwe), to gain insights on opportunities for crop production intensification, and the importance of developing farm-specific nutrient management practices. Investigations on farm typologies have done well in highlighting the fundamental differences between farm categories, with 3–5 typologies often adequate to represent the wide differences in resource endowment. Resource-endowed farmers have ready access to large quantities of manure and mineral fertilizers, which contribute to higher soil fertility and crop productivity on their farms. Resource-constrained households use little or no manure and mineral fertilizers, and have limited capacity to invest in labour-demanding soil fertility management technologies. These farmers often have to rely on off-farm opportunities for income that are largely limited to selling unskilled labour to their resource-endowed neighbors. The variability in management practices by farmers has resulted in three main soil fertility classes that can be used for targeting soil fertility management technologies, characterized by potential response to fertilizer application as: (1) low-responsive fertile fields that receive large additions of manure and fertilizer; (2) high-responsive infertile fields that receive moderate nutrient applications; (3) poorly responsive degraded soils cultivated for many years with little or no nutrient additions. The main conclusions drawn from the review are: (1) resource constrained farmers constitute the widest band across the three countries, with many of the farmers far below the threshold for sustainable maize production intensification and lacking capacity to invest in improved seed and fertilizer, (2) farm sizes and livestock ownership were key determinants for both farmer wealth status and farm productivity, and (3) soil organic carbon and available P were good indicators for predicting previous land management, that is also invariably linked to farmer resource endowment.     

Social, economic and policy dimensions of soil organic matter management in sub-Sahara Africa: challenges and opportunities

In recent years and in some situations the status of soil organic matter (SOM) has deteriorated considerably due to long periods of continuous cultivation and limited external inputs in the form of mineral fertilizers. Deterioration of SOM varies by agro-ecological zones, by soil types and by cropping patterns. It is more intense in East Africa, followed by coastal West Africa and Southern Africa and least intensive in the Sahel and Central Africa. It is also more serious in areas under low-input agriculture irrespective of the prevailing cropping system. The major consequence of the decrease in SOM in the tropics is lower agricultural productivity with a direct negative effect on food security. While biophysical dynamics of SOM have been extensively covered in the literature, social considerations have not received similar attention. This paper examines the social, economic and policy factors associated with the management of tropical soil organic matter. Empirical data from a range of environments in Africa show that SOM improvement options yield a positive return to land as well as labour. However, there are a number of constraints. Social constraints are related to the large quantities of organic matter that are required (case of farmyard manure), the competitive uses for the material (case of crop residues), land and labour requirements, and gender-related issues. From a policy stand point, unsecured tenure rights together with price distortions and other market failures may be important constraints. Challenges for sustainable management of SOM are identified. These include management conflicts, land tenure arrangements, the divergence in goals between individuals and society, land and labour requirements, inadequate support systems for land users, profitability issues, the role of subsidies, and the absence of national action plans. A number of opportunities are identified that could enhance the improvement or maintenance of SOM. These include: exploring the need and potential role of community-based SOM management practices; development of an integrated plant nutrient management strategy involving both organic and inorganic inputs; and development of concrete national action plans. It is argued that because externalities of SOM improvement or maintenance extend beyond the farmer's fields, SOM investment may require cost sharing between individuals and the society. Policies on subsidies need to be reconsidered. Research priorities are identified that require closer collaboration between scientists from a variety of disciplines. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fertilizer use in semi-arid areas of Kenya: analysis of smallholder farmers' adoption behavior under liberalized markets

This paper analyzes the factors influencing farm level fertilizer adoption decisions under an era of liberalized markets in Kenya using a Tobit regression model. The level of education of the household head, experience using fertilizer, growing a cash crop, availability of fertilizer in rural retail outlets, availability in small packages, and land pressure positively influenced fertilizer use, while the size of family labor and location in the drier semi-arid zone were negatively associated with fertilizer use. The paper concludes with policy and research implications for strategies aimed at achieving greater fertilizer use on smallholder farms.     

Beyond adding up inputs and outputs: Process assessment and upscaling in modelling nutrient flows

Departing from the historical background of scientific interest in soil fertility and sustainable agricultural production in sub-Saharan Africa, a review is conducted of nutrient budget studies carried out in semi-arid West Africa at scales ranging from individual fields to the sub-continent. For both, nitrogen and phosphorus, the comparison discloses largely diverging balances calculated for similar agro-ecosystems. In a first step, the modes of calculation of the nutrient budgets are examined. It is demonstrated that the calculations used in the different studies differ by the variables and biophysical processes taken into account, and by the choice of spatial scales as well as related time scales. One important discrepancy between approaches is whether and to which extent nutrient flows are internalized when upscaling. The extent to which the impact of individual and communal management, especially of pastoral and forestry resources, on nutrient flows is accounted for is a second cause of divergence. Moreover, it was observed that nutrient budgets tend to be increasingly negative as the spatial scale of the study increases from farm to sub-continent. This unexpected trend is traced back to the lack of internalization of nutrient flows when upscaling. The complexity of the scale patterns of nutrient flows and that of the interactions and the tradeoffs in the effects of management calls for the use of models to calculate nutrient budgets. Therefore, in a second step, examples of a static model, a multiple-goal linear programming model and a decision rules model were reviewed, all of which include the calculation of nutrient flows and balances and which were applied to West-African farming systems. The models are analyzed for their way of dealing with the critical issues of spatial and temporal scales and the impact of resource management on nutrient flows, taking into account that they have different objectives and were designed for different spatio-temporal scales. To conclude, suggestions were made for strengthening the use of models as tools enabling ex-ante testing of alternative agricultural technologies and policies that could improve soil nutrient balances in semi-arid sub-Saharan Africa.     

Beyond adding up inputs and outputs: Process assessment and upscaling in modelling nutrient flows

Departing from the historical background of scientific interest in soil fertility and sustainable agricultural production in sub-Saharan Africa, a review is conducted of nutrient budget studies carried out in semi-arid West Africa at scales ranging from individual fields to the sub-continent. For both, nitrogen and phosphorus, the comparison discloses largely diverging balances calculated for similar agro-ecosystems. In a first step, the modes of calculation of the nutrient budgets are examined. It is demonstrated that the calculations used in the different studies differ by the variables and biophysical processes taken into account, and by the choice of spatial scales as well as related time scales. One important discrepancy between approaches is whether and to which extent nutrient flows are internalized when upscaling. The extent to which the impact of individual and communal management, especially of pastoral and forestry resources, on nutrient flows is accounted for is a second cause of divergence. Moreover, it was observed that nutrient budgets tend to be increasingly negative as the spatial scale of the study increases from farm to sub-continent. This unexpected trend is traced back to the lack of internalization of nutrient flows when upscaling. The complexity of the scale patterns of nutrient flows and that of the interactions and the tradeoffs in the effects of management calls for the use of models to calculate nutrient budgets. Therefore, in a second step, examples of a static model, a multiple-goal linear programming model and a decision rules model were reviewed, all of which include the calculation of nutrient flows and balances and which were applied to West-African farming systems. The models are analyzed for their way of dealing with the critical issues of spatial and temporal scales and the impact of resource management on nutrient flows, taking into account that they have different objectives and were designed for different spatio-temporal scales. To conclude, suggestions were made for strengthening the use of models as tools enabling ex-ante testing of alternative agricultural technologies and policies that could improve soil nutrient balances in semi-arid sub-Saharan Africa.     

让腐植酸在补充和提升土壤肥力中发挥重要作用——开展“土壤腐植酸肥力综合指数”研究刻不容缓

当前,面对"粮食安全"和"舌尖安全",坚守18亿亩耕地数量与质量"双红线"至关重要。尤其在耕地数量难以增加的情势下,通过提高耕地质量来弥补数量不足,已成为我国农业可持续发展的战略性选择。腐植酸是构成土壤有机质最基本的"核心材料"和本源性物质,其作用贯穿于土壤肥力形成始终。腐植酸又是决定有机质质量的关键因素,工农业副产物的有机质不一定安全,而腐植酸富存的有机质一定安全。凡是有机质不一定是腐植酸,凡是腐植酸一定是有机质。我们有智慧,通过工业化开发利用,促使腐植酸反哺土壤,以提升和补充土壤肥力,实现耕地的良性循环利用和质量的可持续提高。对此,建议国家开展"土壤腐植酸肥力培育产业"的顶层设计,尽快启动"土壤腐植酸肥力综合指数"专项研究,通过确立"腐植酸肥料环境友好产业"的重要地位,把控土壤源头安全生产关。     

Overcoming soil nutrient constraints to crop production in West Africa: Importance of fertilizers and priorities in soil fertility research

The Alfisols, Oxisols, Ultisols and Inceptisols which dominate the soils of West Africa have sustained crop growth for a very long time. As a consequence, their fertility has become perilously low and the task of increasing or even maintaining the productive capacity of these soils has become perhaps the greatest challenge to agricultural scientists in this latter half of the 20th century.Water is useful not only for the growth of plants but also for the efficient use of costly inputs such as fertilizers. On the other hand, fertilizers increase the water-use efficiency. Such interactions must be closely studied so as to maximize the impact of inputs of agricultural production.The nutrients in the soil are always in a state of flux, with additions and subtractions. Monitoring the dynamics of the nutrients would promote their efficient use by crops and prolong the productive life of the soils.Several models currently exist for the study of organic matter dynamics in soils. These models should be applied to the West African situation since it is vital to develop management practices that can promote efficient use of nutrients released during mineralisation of soil organic matter.Judicious fertilizer use in West Africa should be promoted as this practice will enhance agricultural production while protecting the fragile environment.     

Managing soil fertility diversity to enhance resource use efficiencies in smallholder farming systems: a case from Murewa District,Zimbabwe

Smallholder farms in sub-Saharan African exhibit substantial heterogeneity in soil fertility, and nutrient resource allocation strategies that address this variability are required to increase nutrient use efficiencies. We applied the Field-scale resource Interactions, use Efficiencies and Long-term soil fertility Development (FIELD) model to explore consequences of various manure and fertilizer application strategies on crop productivity and soil organic carbon (SOC) dynamics on farms varying in resource endowment in a case study village in Murewa District, Zimbabwe. FIELD simulated a rapid decline in SOC and maize yields when native woodlands were cleared for maize cultivation without fertilizer inputs coupled with removal of crop residues. Applications of 10 t manure ha⁻¹ year⁻¹ for 10 years were required to restore maize productivity to the yields attainable under native woodland. Long-term application of manure at 5 and 3 t ha⁻¹ resulted in SOC contents comparable to zones of high and medium soil fertility observed on farms of wealthy cattle owners. Targeting manure application to restore SOC to 50–60% of contents under native woodlands was sufficient to increase productivity to 90% of attainable yields. Short-term increases in crop productivity achieved by reallocating manure to less fertile fields were short-lived on sandy soils. Preventing degradation of the soils under intensive cultivation is difficult, particularly in low input farming systems, and attention should be paid to judicious use of the limited nutrient resources to maintain a degree of soil fertility that supports good crop response to fertilizer application.     

Management of soil organic matter in semiarid Africa for annual cropping systems

Ensuring sustainable agriculture in semiarid Africa requires the implementation of methods to balance nutrients and to conserve soil organic matter (SOM). There is an urgent need to improve the management of all types of SOM input. In this paper; the authors review a wide range of agricultural practices and discuss their advantages, limitations and feasibility. They distinguish ‘traditional systems’ such as traditional fallow, parkland and manuring from ‘improved systems’ such as ‘improved fallow’, forest fallow, alley cropping, cover crops and application of composted manure. Biomass production (BMP) for ‘improved systems’ is mainly linked: (i) for agroforestry, to the tree species used in forest fallow, to the synchronization of nutrient supply by the soil with the cereal demand in alley cropping, and generally to the efficiency of the root system and its development with the depth; (ii) for cover crops, BMP is mainly linked to the initial soil fertility and to the ecological zone: establishment and management of cover crops are not yet fully mastered under some conditions such as an annual rainfall below 800 mm and/or on very clayey soils; (iii) for manure, BMP is mainly linked to the improvement of fallow in order to ensure sufficient forage resources. Because semiarid Africa is mainly a livestock zone, the authors emphasise manure: constraints, quality indicators and tools used to encourage its production, are analysed. Thus it was concluded that the intensification of manure production and its rational use in semiarid African regions, threatened by drought and malnutrition, is very important: this cannot be separated from the production of plant biomass, whose possibilities have been examined above. This revised version was published online in June 2006 with corrections to the Cover Date.     

Accumulation and apparent recovery of N,P and K after the incorporation of gliricidia and manure in intercropping during the cultivation of corn–cowpea–cotton

Fertilization with manure is widely adopted by farmers in the semiarid region of northeastern Brazil, although the quantity of available manure is limited. Thus, among other alternatives, gliricidia has been used as an additional source of organic fertilizer. The objective of this study was to evaluate the accumulation and apparent recovery of N, P and K after using different forms of gliricidia and manure application in the intercropping of corn, cowpea and cotton in three crop cycles in the semi-arid northeast region of Brazil. The following treatments were used: gliricidia incorporated into the soil before planting; gliricidia spread on the surface of the soil at 45 days after planting; manure and gliricidia incorporated into the soil before planting; manure incorporated into the soil before planting and gliricidia spread on the surface of the soil at 45 days after planting; manure incorporated into the soil before planting; and no addition of organic fertilizer (control). Accumulations followed the same pattern as biomass production but differed greatly from the concentrations. Low apparent recoveries were obtained in the first and second cycles, and high apparent recoveries were obtained in the third cycle. The nutrient balances indicated that the incorporation of gliricidia before planting or spread on the surface does not meet crop needs. The incorporation of manure as well as manure and gliricidia when applied on the surface, were able to meet growth needs and maintain soil fertility.     

Fertiliser use and definition of farmer domains for impact-oriented research in the northern Guinea savanna of Nigeria

One of the options to alleviate soil fertility constraints for sustainable agriculture in the savannas of West Africa is to develop soil nutrient management technologies from an adequate supply and feasible share of organic and mineral inputs. This paper makes a diagnosis of farm-level use of organic and inorganic inputs, as a basis for the development of technologies.The results from the diagnosis are then used to develop a framework for characterizing farmers for impact-oriented research on soil nutrient management systems. The survey was carried out with 200 farmers carefully selected in two villages in the northern Guinea savanna of Nigeria. The results showed that more than 90% of farmers in both villages used chemical fertilizers. This is contrary to a general belief that they are not widely applied to food crops by small holders in African agriculture. However, up to 81% of the fields received less than half of the recommended 120 because of high costs due, probably to removal of subsidies and inefficient marketing systems. Organic inputs such as animal manure were applied in very small quantities (about 8% of the requirements). However there is evidence of integrated use of inorganic fertilizers and organic manure on some(24%) of the fields. The problem to be addressed is that of the production (and efficient utilisation) of organic inputs in the northern Guinea savanna. Nitrogen deficiency is the most limiting soil nutrient in the cereal-dominated systems of study area. On this basis, farmers were classified into two a-priori groups using a threshold of 30, and multiple quantitative variables were fitted in a discriminant analysis tovalidate the typology. Results indicated that more than 75% of farmers were well classified into two groups that had the characteristics of thea-priori groups. Two others were a typical and included the remaining 25% of farmers. Thus, there are a total of four groups of farmers referred to as farmer domains in this paper. The two domains with 75% of well-classified individuals are suitable for the selection of farmers with whom to conduct applied research or for development activities because they represent the general patterns in the supply and use of soil nutrients in the study area.Although basic research can be done in the four domains, the two atypical groups are most suited for process-level studies to improve the understanding of factors that make the systems either more efficient or less efficient than the two other farmer domains. In either case, representative farmers were easily identified by their highest probability of belonging to a specific domain from the model results. Multivariate models constitute a good framework to make a typology of, and to select farmers for, participatory research and extrapolation of results in the northern Guinea savanna. This revised version was published online in June 2006 with corrections to the Cover Date.