Integrated Soil Management Research Articles

Soil Organic Carbon Fractions and Enzymes Activities as Affected by Organic and Inorganic Amendments in an Acid Soil of Meghalaya

Soil organic carbon (SOC) and its fractions (labile and non-labile) are important for sustainability of any agricultural production system as they govern most of the soil properties, and hence soil quality and health. Being a food source for soil microorganisms, they also affect microbial activity, diversity and enzymes activities. The present paper reports the results from a three years (2011–14) field experiment to elucidate the effect of soil amendments (lime and FYM) on SOC fractions and enzymes activity. Results revealed that integrated soil management comprising 50% NPK+FYM @ 5 t ha−1+Lime @ 0.5 t ha−1 significantly improved the SOC fractions, and the proportional changes were more in the labile SOC fractions. Soil enzymes activities were also better correlated with the labile SOC fractions. Rhizosphere soil had proportionally more amount of labile organic carbon (LBC) over total organic carbon (TOC), and also had better enzymatic activities than non-rhizosphere soil. This experiment shows that proper combination of soil amendments improves the SOC fractions, and changes would be more readily reflected by the labile SOC fractions. Soil enzymes activity, which is directly related with the labile SOC fractions, is a good indicator of changes induced by various management practices. Relative changes in the SOC fractions and soil enzymes activity are more pronounced in the rhizosphere than in non-rhizosphere soil.

Assessment of soil health indicators for sustainable production of maize in smallholder farming systems in the highlands of Cameroon

Agricultural intensification has been recognized as one of the solutions to increase food production to feed the ever-increasing population in sub-Saharan Africa. This can partly be achieved if quantitative and up-to-date information on soil health indicators are not available. This study used the land health surveillance framework, which combines ground-sampling schemes based on sentinel site and infrared spectroscopy to select a minimum dataset of soil health indicators to identify key land constraints for maize production and target potential interventions. We found high variability in soil properties in the study area which was mainly due to inherent soil conditions and land management practices. The most variable soil properties (CV>0.38) were nitrogen (N), electric conductivity (ECd), exchangeable bases (ExBas), boron (B), calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn) and phosphorus (P). Moderate variability (0.2<CV<0.38) was observed for carbon (C), silt and sand, while properties with least variability (CV<0.2) were pH and aluminium (Al). The effects of land-use and soil depth were significant (p<0.05) for most of the soil properties. Principal component analysis (PCA) identified soil nutrient availability, metal concentration and texture as the three main factors that explain most of the variability observed. Significant interactions were observed between soil properties confirming the need for a minimum dataset of indicators. ExBas, B, pH, Mn, ECd, P and clay content formed the minimum dataset of soil health indicators for the study area. The results also showed that the soils of the study site are marginally suitable for the production of maize (Zea mays L.). Low limitations with respect to exchangeable bases (Ca, Mg, K and Na) and severe limitations with respect to B (<0.15mgkg−1), pH (<6.20), P (<6.5mgkg−1 soil) and clay content (>63%) were detected. However, potential for improvement exists through integrated soil management practices that include the use of organic and inorganic fertilizers, minimum soil tillage, and inclusion of legumes in crop rotations that could improve soil physical and chemical properties.

English

The study was conducted in the Kimbibit District, which is located at the North Shoa Zone of Oromia National Regional State, with the objective of investigating the effects of traditional practice of soil burning (guie) on physical properties of soils of the study area. Both disturbed and undisturbed soil samples were collected from farmers’ burned fields and normal fields in three peasant associations. The burned soils samples were collected from the bottom, middle and top of the heap. Soil parameters were analyzed using standard procedures and the results were subjected to analysis of variance (ANOVA). Mean separation was done using the least significant difference (LSD). Except silt content, total porosity, percentage base saturation, all the other parameters considered in this study were significantly affected by soil burning. The burning reduced clay content (71.9, 78.4 and 75.8%), total porosity (20.3, 21.7 and 0.1%), water retained at FC (26.0, 58.4 and 33.8%) and PWP (19.7, 55.5 and 25.0%) and available water holding capacity (42.9, 67.1 and 57.1%), of the bottom, middle and top of the heap, respectively. Burning increased sand content (31.0, 38.0 and 34.5%), bulk density (19.7, 30.3 and 9.2%), particle density (7.7, 16.3 and 9.5%), water repellency (84.0, 149.4 and 95.1), on the bottom, middle and top of the heap, respectively. The soil attributes due to soil burning showed an overall change towards the direction of the loss of its physical fertility as compared to unburned soils. Therefore, strategies to feed the expanding population in the study areas will have to seek a sustainable solution that better address integrated soil management. Key words: Guie, heap, Kimbibit district, soil burning.

프랙탈 차원 해석을 통한 인위토양과 자연토양 비교

In general, fractal analysis which is based on self-similarity as a basic theory has been mainly used to define the characteristics of complex mathematical figures, however, considering its basic theory, it can be also used to analyze the surface ununiformity of unknown materials. In this study, the soil samples were collected from the reclaimed (remodelled) agricultural fields which mean that the external soil is artificially piled up (mainly up to 1m) on the lands, Naju, Jellanam-do and Gumi, Gyeongsangbuk-do, and the conventional agricultural fields, Anseong, Gyeonggi-do and Hwasoon, Jellanam-do, and compared using fractal dimension analysis on the basis of the results of chemical properties. The score of fractal dimension (<TEX>$D_0$</TEX>) for organic matter was lower in Hwasoon (1.46) and Naju (1.58) than Anseong (1.86) and Gumi (1.96), and this trend showed similarly in soil pH. On the basis of the results of chemical properties, fine textured-soils (Hwasoon and Naju) and conventional agricultural fields were chemically uniform compared to coarse textured-soils (Anseong and Gumi) and the reclaimed. Therefore, it is required to develop technical methods for integrated soil management to the reclaimed lands.

English

The knowledge of soil properties and availability of reliable soil data play vital role in understanding the soil environment and its services. This study was conducted with the objective of characterizing and classifying soils of Wadla Delanta Massif, North Central Highlands of Ethiopia. Twelve representative soil pedons (profile pits) were opened on various landscape positions, described in the field and horizon-wise samples collected for morphological and physicochemical analysis. Variations in color (moist and dry) within a pedon and among pedons along the toposequence were observed with grayish, dark brownish or black colors dominating the surface layers, while stronger and brighter colors with shades of reddish brown and light brownish gray dominated the surface layers. The soils are heavy clays (35 to 80%), of low bulk density (1.02 to 1.35 g cm-3), acceptable ranges of particle density for mineral soils (2.41-2.82 g cm-3) relatively high total porosity (46.51-60.55%), and high available water holding capacity (129.9-287.9 mm m-1).The soils were slightly acidic to moderately alkaline (6.25 to 8.29) in their reaction, salt free (EC &lt; 0.5 dS m-1), very low to medium in organic matter (0.12 to 4.82%) and total N (0.02 to 0.28%) contents, and available P (0.52 to 18.44 mg kg-1), high to very high in CEC (31.98 to 65.48 cmolc kg-1), exchangeable bases and base saturations (60.22 to 98.97%), with medium status of micronutrients occurring in order of Fe (0.82-10.40 mgkg-1) &gt;Mn (2.01-9.22 mgkg-1) &gt; Cu (0.80-6.03 mgkg-1) &gt; Zn (0.80-5.80 mgkg-1), all of which were above the critical limit. Based on morphological, physical and chemical analysis, and the FAO-WRB Soil Classification System, the soils are classified as Mazi-Pellic Vertisols, Mazi-Calcic Vertisols, Haplic Cambisols and Mollic Leptosols. The soil potentials are hampered by their stickiness when wet and hard when dry, waterlogging and soil erosion due to inappropriate tilling and timing of cultivation. Therefore, integrated soil management is essential in the area. &nbsp; Key words: Altitude, horizon, pedon, topography.&nbsp

Source of technical inefficiency of smallholder wheat farmers in selected waterlogged areas of Ethiopia: A translog production function approach

This study was undertaken to investigate the technical inefficiency and factors affecting efficiency of wheat production in water-logged areas of Arsi-robe and Digelu-tijo districts of Arsi zone in southeastern Oromia region, Ethiopia. Both purposive and two-stage sampling techniques were used. Primary data was collected from 157 randomly selected wheat producing farmers through a structured questionnaire. The translog production function analysis revealed that the mean technical efficiency of wheat producers in the study areas in the season were 55%. Given the present state of technology and input level, the result of the study suggests that there is plenty of scope to increase the output of wheat commodity by up to 45%. Education, gender, fragmentation (number of wheat plots), and access to input and output markets have negative coefficients in the inefficiency model. In addition to this, the study indicates scaling up/out of best farmers’ practices in the use of recommended integrated soil, water and nutrient management practices is essential for improving the productivity of commercial wheat varieties grown under water-logged vertisols. Furthermore, sharing the benefits of improved technologies through informal education and field days in demonstration plots could be important possible interventions for obtaining maximum achievable wheat yield under the difficult growing conditions of water-logged vertisols in Ethiopia. Key words: Technical inefficiency, stochastic frontier, production function, wheat farmers, Vertisols.

Erratum to: Integrated soil and plant phosphorus management for crop and environment in China. A review

Erratum to: Integrated soil and plant phosphorus management for crop and environment in China. A review

An Investigation into the Problem of Crop Failure at the Chathina Irrigation Scheme, Chingale, Zomba District in Malawi

Evaluation studies were conducted to determine the possible causes of the crop failure problem at Chathina Irrigation Scheme and to suggest soil management strategies for addressing the causes for crop production improvement. A detailed soil survey of the area was conducted to determine the extent of different soil types existing in the area. Collected soil and irrigation water samples were analysed for physical- chemical properties at Bvumbwe Soils Laboratory. Three distinctive soil types were identified: Soil Type 1: Compact Soil (Colluvial Soil); Soil Type 2: Cracking Heavy Soil (Vertisols, Makande) with Sub-Soil Type 2a: Stratified Vertisols, and Sub- Soil Type 2b: Uniform Vertisol; Soil Type 3: Brownish Loamy Soil (Alluvial Soil) with Sub-Soil Type 3a: Stratified Brown Loamy Soil (Young Alluvial) and Sub-Soil Type 3b: Uniform Brown Loamy Soil (Old Alluvial Soil). The identified problems causing crop failure in the scheme were: low natural soil fertility; high soil salinity; high soil sodicity; poor quality irrigation and high water tables. Different integrated soil management technologies and tolerant crops were recommended. Follow-up studies were also suggested.

Improving the productivity of lowland soils for rice cultivation in Ghana: The role of the Sawah system

Lowlands constitute one of the largest and appropriate environments suitable for rice cultivation in Ghana. However, environmental degradation and declining soil productivity, leading to low crop yields are major concerns. Some reasons leading to such concerns may be traced to lack of proper management of our soil resources and possible unsuitable crop production systems and practices. Effective nutrient and water management in addition to suitable land preparation options are key factors for the effective and sustainable utilization of these inland valley ecosystems. Proper and meaningful management strategies therefore need to be developed in a way as to enable and encourage farmers to accept and easily adopt them. Designing and implementation of comprehensive and integrated soil management programs that will not only improve and maintain soil fertility but also make maximum use of available water are necessary. While research has shown that these environments vary considerably in soil type, water holding capacity and nutrient retention, it has been further observed that soils of most valleys are dominant in low activity clay minerals which have low nutrient and water holding capacities. Adoption of the “Sawah” system will enhance and sustain production. The Sawah system is characterized by nutrient replenishing mechanisms with intrinsic resistance to erosion (better water control and nutrient management). Rice responds better to fertilizer (mineral and organic) under the Sawah system than the traditional system of rice production in Ghana. Rice cultivation under the “Sawah” system in inland valleys in Ghana has lead to significant improvement in soil and water management. There has been a gradual and significant increase in rice grain yield in the order: farmers practice < only bunded < bunded and puddled < bunded, puddle and leveled (“sawah”), across locations and varieties. An integration of available farm manures with mineral fertilizer resulted in significant increases in paddy grain yield across locations, thus reducing the over reliance of famers on mineral fertilizers to improve soil fertility. From a significant initial increase (from less than 1.0 t ha -1 to over 4.5 t ha -1 ), mean paddy grain yield under the “Sawah” system consistently and continuously increased annually and currently stands at over 6.0 t ha -1 among farmer groups. Mean net income generated per hector under the “sawah” system also ranged from US $1,500 to US $2,800 over the same period among farmer-groups. There was also a gradual build up of total carbon and exchangeable bases (K, Ca, Mg) leading to improved nutrient levels, even though there was a net loss of both total Nitrogen and available Phosphorus over the same period. Ghana (possibly West Africa) has the potential to increase local rice production by over 300% when the “Sawah” system is adopted. Key words: Lowlands, improvement, rice yields, sawah system, soil productivity.

SOIL SUPPRESSIVENESS TOWARDS MELOIDOGYNE, VERTICILLIUM OR PYTHIUM IN GREENHOUSE HORTICULTURE

Soils originating from fourteen greenhouse horticultural companies were assessed for the level of suppressiveness of three major pathogens of vegetables and flowers, namely the root knot nematode Meloidogyne incognita, Pythium aphanidermatum and Verticillium dahlia. As controls, three well-documented soils in terms of disease suppressiveness and coarse sand were included for each pathogen. Soils were distributed over three treatments with forty replicates each in a random block design under standardized conditions. Each soil was treated with ?-radiation in order to assess the contribution of abiotic properties to disease suppressiveness. Non-sterilized soils served as a measure of abiotic- and biotic factors, and soil without the addition of pathogens served as a control to determine background contamination of indigenous pathogens. Soils were acclimatized for one week. Afterwards, irrigation was started and pathogens were inoculated. Survival stages of V. dahlia or P. aphanidermatum were added as pure suspensions, i.e., microsclerotia or oospores, respectively. For Meloidogyne, second stadium larvae (J2) were used. Seedlings were planted for M. incognita, while for P. aphanidermatum and V. dahlia, seeds were used. A large variation in the level of suppressiveness was observed. Soil suppressiveness towards Meloidogyne, Verticillium or Pythium was not correlated. This means that suppressiveness is pathogen dependent. However, soil structure contributes to a large extent to the level of suppressiveness as exemplified by the survival rate of Meloidogyne and Pythium in sandy soils. With this dataset we aim to unravel the underlying mechanisms and investigate whether suppressiveness levels can be increased and used in an integrated soil management system.

Integrated soil management – moving towards globally sustainable agriculture

SUMMARYThis review introduces the main concepts behind integrated soil management (ISM) and examines the ways in which it currently operates. It suggests the scope for future technological development. The review also highlights the potential of ISM to address the challenge of meeting the demands of the increasing world population, while maintaining sustainable agro-ecosystems, as judged from long-term soil fertility, environmental and socio-economic perspectives. Changes to policy, governance and funding worldwide will be needed to conserve and manage the soil resource, and to restore already degraded systems. Research should be prioritized to ensure continued delivery of new soil technologies. Such changes must engage all land-use stakeholders, must involve educational, training and extension programmes and must embrace the multidisciplinarity required for effective soil conservation and management.

Integrated soil management in eroded land augments the crop yield and water-use efficiency

Cultivated lands in erosion prone agro-ecologies incessantly experience a substantial loss of productive soil and organic matter. Currently, the fertility-management and rainwater-conservation practices are given emphasis separately. This study appraised collectively both the water-conservation and fertility-management practices for the restoration of soil productivity in eroded farmlands. Field experiments were carried out on wheat (Triticum aestivum L.) and maize (Zea mays L.) in eight farmer fields. Four fields of Missa soil series (Typic Ustochrept) and four of Rajar soil series (Typic Ustorthent) were selected. Treatments in each field were: farmers' practice as control without soil-water conservation, and with farmers' rate of fertilizer (per hectare 40 kg N + 30 kg P2O5); improved fertilization (per hectare 100 kg N, 60 kg P2O5, 2 kg Zn, and 1 kg B) without soil-water-conservation practices; soil-water-conservation practices (deep plowing, bund improvement, ploughing across the contour) + farmers' rate of fertilizers; and soil-water conservation + improved fertilization. Crop grain yields were at the highest with soil-water conservation + improved fertilization (per hectare wheat 3.31 Mg and 1.65 Mg in 2004–2005 and 2005–2006; and maize 4.55 Mg and 4.19 Mg in 2005 and 2006, respectively). The lowest yields were recorded under farmers' practice for both crops. Similar was the response for water-use efficiency and plant uptake of nitrogen, phosphorus, zinc, and boron. Missa soil series was more responsive than was Rajar to integrated soil-management practices. Synergistic application of soil-water conservation and improved fertilization practices significantly improved the crop yields, nutrient uptake, and water-use efficiency.

Estimation de la fertilité potentielle des ferralsols par la couleur

A farmer-friendly method of determining the most suitable cultivation soils would help in transferring new integrated soil management technologies. The potential for using soil color (Munsell data) was tested by physico-chemical analysis of 1028 ferrallitic soil samples from 289 profiles unequally allocated above 7 deg N in Côte d’Ivoire. Soil hue variations in depth and along the toposequence revealed the existence of vertical and lateral gradients of soil hue. The relative contribution of the different descriptors (clay, sand, carbon, total nitrogen, total phosphorus, potassium, magnesium and calcium) to the three functions extracted using a discriminant analysis to differentiate the four groups of soils with different hues was evaluated as well as the analysis of variance to determine the possible groups number for each one of the descriptors. Differences between physico-chemical components of red (2.5YR and 5YR) and yellow (7.5YR and 10YR) soils were determined, especially for P, Mg and K in extension. A decreasing gradient of inherent soil fertility indicators with an increasing yellowness in soil hue was revealed using multiple regression models. The soils 2.5YR and 5YR were therefore deemed more appropriate for stable and sustainable agriculture.Key words: Hue, ferralsols, fertility, soil use

Citrus Decline: Soil Fertility and Plant Nutrition

ABSTRACT Soil physical properties related constraints (clay gradient in soil profile, drainage/irrigation/waterlogging) and soil fertility constraints induced by soil pH, salinity (specific ion-and cumulative osmotic pressure effect), calcareousness (pedogenic or non-pedogenic CaCO3), besides increasing menace of nutrient mining, are the important pedological factors contributing to citrus decline. But, the orchards established on later two soil orders confronted with subsurface constraints in form of argillic (clay rich horizon with acidic or alkaline pH and varying intensity/forms of calcareousness) and spodic horizonation (organic hardpan with very acidic pH), in addition to multiple soil fertility constraints. Soil condition-based rootstock alternatives, site specific nutrient management coupled with variable rate application, and integrated soil management systems representing different modules of INM, are the viable means of combating an untimely decline in citrus orchards’ productivity.

Effect of Organo- mineral fertilizer Application on growth and yield of French- beans (&lt;i&gt;Phaseolus vulgaris&lt;/i&gt; L.)

The main constraints to sustainable crop production in arid environment are mainly inherent low fertility of the soil and moisture deficit. A study was conducted at Mekelle University, Tigray Region in Ethiopia to test the hypothesis that Integrated soil management practices consisting of manure (Cow dung) and Inorganic fertilizers (Urea and Dap) in combined form, thereby resulting in higher yields and fertilizer use efficiency, resulted in high productivity with reduced risk. Results from an analysis of variance showed that the high combination of organic and inorganic manure gave higher yields. Among the nutrient applications, the combination of high amount of urea with manure gave higher yields than the use of either higher amount of Dap, Urea with lower manure and unfertilized plot. There was significant difference among all the treatments consider: fresh weight, leaf area, plant stand and plant height. Returns from French beans grown with higher fertilizer combination rates (100kg urea, + 125kgDap and 3.75tones of manure were found to be the most profitable in terms of high returns and low risk, mainly because higher fertilizer use efficiency and residual effects on the soil properties than any of the treatments. The study recommends combined use of organic and inorganic manure with no effects on higher rate of manure combination for the arid environment as an insurance against total crop failure. Keywords: Organic, Inorganic fertilizers, Urea, Dap, yield, growth, French bean Ethiopian Journal of Environmental Studies and Management Vol. 1 (3) 2008: pp. 8-17

Role of Legume Fallow in Intensified Vegetable-Based Systems

Traditional shifting cultivation systems can no longer be sustained in intensive vegetable production systems of southwestern Nigeria. Alternative cropping systems include the use of site‐specific, weed‐suppressing, multipurpose cover legumes as short‐duration crops while reducing production costs. The purpose of this study was to investigate an integrated soil management system with leguminous cover crops in vegetable‐based systems. One year, planted fallow of leguminous cover crops Aeschynomene histrix, Canavalia ensiformis, Centrosema pubescens, Chamaecrista rotundifolia, Crotolaria ochroleuca cv. “Utiisp”, Mucuna Ghana, Mucuna pueraria cv. “IRZ”, Mucuna puriens cv. “Utilis”, Mucuna rajada, Pueraria phaseolodies, Stylosanthes hamata, and natural grass fallow as a control were followed by sweet maize (Zea mays cv. “TZSR‐sweet”) and vegetable amaranth (Amaranthus hybridus cv. “NHAc3”) in the second year, with 0 or 60 kg nitrogen (N) ha−1 as urea. Results showed that ground coverage by the cover crops within the first 3 months after planting (MAP) was highest in Crotolaria and lowest in Centrosema. At 5 MAP, Crotolaria had the highest biomass accumulation followed by Canavalia, Aeschynomene, and Mucuna cv. “IRZ”. Mucuna puriens cv. “Utilis” had a significantly higher soil total N compared with the grass fallow. Legume rotation increased vegetable yields and N accumulations. Legume fallow appeared to offer potential to sustain vegetable yields under intensified cropping. However, the absolute effect varied as a function of legume species and N‐management practices.

Soil management practices for sustainable agro-ecosystems

A doubling of the global food demand projected for the next 50 years poses a huge challenge for the sustainability of both food production and global and local environments. Today’s agricultural technologies may be increasing productivity to meet world food demand, but they may also be threatening agricultural ecosystems. For the global environment, agricultural systems provide both sources and sinks of greenhouse gases (GHGs), which include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). This paper addresses the importance of soil organic carbon (SOC) for agro-ecosystems and GHG uptake and emission in agriculture, especially SOC changes associated with soil management. Soil management strategies have great potential to contribute to carbon sequestration, since the carbon sink capacity of the world’s agricultural and degraded soil is 50–66% of the historic carbon loss of 42–72 Pg (1 Pg=1015 g), although the actual carbon storage in cultivated soil may be smaller if climate changes lead to increasing mineralization. The importance of SOC in agricultural soil is, however, not controversial, as SOC helps to sustain soil fertility and conserve soil and water quality, and organic carbon compounds play a variety of roles in the nutrient, water, and biological cycles. No-tillage practices, cover crop management, and manure application are recommended to enhance SOC storage and to contribute to sustainable food production, which also improves soil quality. SOC sequestration could be increased at the expense of increasing the amount of non-CO2 GHG emissions; however, soil testing, synchronized fertilization techniques, and optimum water control for flooding paddy fields, among other things, can reduce these emissions. Since increasing SOC may also be able to mitigate some local environmental problems, it will be necessary to have integrated soil management practices that are compatible with increasing SOM management and controlling soil residual nutrients. Cover crops would be a critical tool for sustainable soil management because they can scavenge soil residual nitrogen and their ecological functions can be utilized to establish an optimal nitrogen cycle. In addition to developing soil management strategies for sustainable agro-ecosystems, some political and social approaches will be needed, based on a common understanding that soil and agro-ecosystems are essential for a sustainable society.

Implications of local soil knowledge for integrated soil management in Latin America

The increasing attention paid to local soil knowledge in recent years is the result of a greater recognition that the knowledge of people who have been interacting with their soils for long time can offer many insights about the sustainable management of tropical soils. This paper describes two approaches in the process of eliciting local information. Case studies show that there is a consistent rational basis to the use of local indicators of soil quality and their relation to improved soil management. The participatory process used is shown to have considerable potential in facilitating farmer consensus about which soil-related constraints should be tackled first. Consensus building is presented as an important step prior to collective action by farming communities in integrated soil management at the landscape scale. Taking advantage of the complementary nature of local and scientific knowledge is highlighted as an overall strategy for sustainable soil management.

Food Insecurity, Soil Degradation and Agricultural Markets in West Africa: Why Current Policy Approaches Fail

The agricultural sector in West Africa is not at present capable of meeting the growing demand for food for its population and of reversing unfavourable trends in soil degradation. We argue that integrated soil management is an essential condition for sustainable agricultural development in the many regions in West Africa where population pressure forces an intensification of land use. Such an approach combines improved soil-moisture storage measures, and the use of organic and inorganic fertilizers and soil amendments. The synergetic effects which could result from this combination are indispensable for achieving the productivity increases needed to cope with the pressure of population. Current (neo-liberal and ecological-participationist) policy approaches are unable to realize the transition towards integrated soil management technologies. The time lags involved in learning to use new technologies, in the adaptation of technologies to local circumstances, and in reaping the benefits of soil fertility investments call for (at least temporary) support of agricultural incomes.

Integrated soil management for the savanna zone of W. Africa: legume rotation and fertilizer N

Integrated soil management with leguminous cover crops was studied at two sites in the northern Guinea savanna zone of northern Nigeria, Kaduna (190 day growing season) and Bauchi (150 days). One-year planted fallows of mucuna, lablab, and crotalaria were compared with natural grass fallow and cowpea controls. All treatments were followed by a maize test crop in the second year with 0, 30, or 60 kg N ha−1 as urea. Above ground legume residues were not incorporated into the soil and most residues were burned early in the dry season at the Kaduna site. Legume rotation increased soil total N, maize growth in greenhouse pots, and dry matter and N accumulation of maize. Response of maize grain yield to 30 kg N ha−1 as urea was highly significant at both sites and much greater than the response to legume rotation. The mean N fertilizer replacement value from legume rotation was 14 kg N ha−1 at Kaduna and 6 kg N ha−1 at Bauchi. W ith no N applied to the maize test crop, maize grain yield following legume fallow was 365 kg ha−1 higher than natural fallow at Bauchi and 235 kg ha−1 higher at Kaduna. The benefit of specific legume fallows to subsequent maize was mostly related to above ground N of the previous legume at Bauchi, where residues were protected from fire and grazing. At Kaduna, where fallow vegetation was burned, maize yield was related to estimated below ground N. The results show that legume rotation alone results in small maize yield increases in the dry savanna zone.