1237 92 - 12/63
Review, tropics, symposium, soil fertility, plant production, soil constraints, sustainability
Trop. Agric. Res. Series No. 24; Trop. Agric. Res. Center (TARC), Tsukuba, Ibaraki, 305 Japan; ISSN 0388-9386, 1991, 216 pp.
Generally it is recognized that the tropical and sub-tropical countries and regions are faced with various kinds of soil constraints on sustainable plant production in cultivated lands, pastures and agroforestry schemes, which are presumably caused by fertility, acidity and salinity, erosion, micronutrient deficiency or excess, physical, chemical and biological limitations.
On behalf of the Symposium Organizing Committee of the Tropical Agriculture Research Center (TARC), the "International Symposium on Soil Constraints on Sustainable Plant Production in the Tropics" under the co-sponsorship of the TARC, Ministry of Agriculture, Forestry and Fisheries, Japan, was held.
The TARC was established in 1970 with the objective of contributing to the development of agricultural technology in the tropical areas in undertaking research programs.
The TARC activities cover a fairly wide range of research fields such as crop production, soil and water management, plant protection, pasture and animal husbandry, agriculture and food engineering, forestry and agroforestry.
In the symposium discussed here, the causes of the constraints are evaluated based on scientific data. The establishment of relevant measures for their alleviation with emphasis placed on low-input and sustainable plant production, in taking account of the preservation of the co-systems and environment in the tropics and sub-tropics are discussed.
This book is organized in country reports, technical reports and closes with a general discussion.
The book provides an overview of soil-based constraints which are limiting the sustained productivity of agriculture. It covers the research activities on characterization, genesis and amelioration of soil-related physical, chemical, and biological constraints. Some of the constraints are natural whereas others have arisen due to human interventions. Waterlogging and salinization in irrigation commands of arid and semi-arid regions, overmining of nutrients, and excessive exploitation of underground fresh waters have decreased the productivity of crops in several regions of the tropics. Alternative methods of soil management for improvement of degraded land qualities, and maintenance of environment and productivity of the soil resources are discussed.
1238 92 - 12/64
Europe, review, soil pollution, agricultural practices, plant nutrients, fertilizer, pesticides, animal excreta, water athmosphere
PAIN, B. et al.
Outlook on agriculture, 20, 3, 1991, pp. 153-160
There is a growing appreciation of the need to preserve soils and their chemical status.
There is an urgent requirement to understand and quantify the various inputs and outputs in order to devise protection policies for this key resource.
This paper focuses on the problems that result from high inputs of plant nutrients, from fertilizers or animal excreta, and from the pesticides that are associated with intensive production. Concern is not only about the direct effects on soils but also on leakages to both water and the atmosphere.
Soils are the base resource for food production.
Their physical and chemical properties are wide-ranging, allowing them to act as sinks or sources in complicated cycles and buffer changes in the flows of materials to other compartments of the ecosystem.
Man's activities can disturb the equilibria involved through
- manufacturing and energy-related activities, resulting in atmosheric inputs of sulphate, acidity, nitrogen (N) and trace metals, for example, or indeed accidental inputs of radio- nucleides,
- urbanization, resulting in direct losses or changes due to recreational activities and
- agricultural manipulations.
The effects of agriculture can be physical, induced by mechanically working the soil in an inappropriate way to result in, for example, soil compaction or erosion, or they may be chemical.
This article is concerned with some of the problems associated with chemical changes.
In detail, the effects of fertilizers, slurries and manures from housed livestock and pesticides are discussed.
1239 92 - 12/65
USA, field study, greenhouse study, organic biostimulants, low-input agriculture, forestry, horticulture, plant growth, stress resistance, fertilizer application, organic agriculture
RUSSO, R.O. and G.P. BERLYN
Journal of Sustainable Agriculture, 1, (2), 1991, pp. 19-42
Organic farming maintains soil quality better and reduces contamination of air, water, soil, and final food products, but much research is needed to determine how to maximize the integration of organic practices.
Methods of increasing fertilizer efficiency must be investigated.
The approach to increasing crop productivity is the development of non-polluting organic biostimulants. These compounds increase plant growth and vigor through increased efficiency of nutrient and water uptake. Definitions for biostimulants vary greatly and there are still some arguments surrounding these compounds. However they are defined as on-fertilizer products which have a beneficial effect on plant growth.
Many of these biostimulant materials are natural products that contain no added chemicals or synthetic plant growth regulators. The initial empirical image of these compounds is changing.
An overview of some of the individual components of the biostimulant blend is given in this paper.
Studies were aimed to test different concentrations (dilutions) of the biostimulant.
Research at the Yale University School of Forestry and Environmental Studies has developed, a new biostimulant (ROOTS). The product consists of a mix of humic acids, algae extracts, a non-hormonal reductant plant metabolite, and vitamins. This blend greatly increases root and top growth of plants, while decreasing fertilizer requirements up to 50% in a number of species (coffee, several grass species, pines, Douglas-fir, Gliricidia). The biostimulant also increases resistance to low soil water potential and possibly residual herbicides in soil.
The organic biostimulant, ROOTS, seems to offer a significant opportunity to increase plant growth, according to findings from current university research and field trials. Improved root and shoot growth, better root growth potential, and better stress resistance seem to be consistent with other results. The most important possibility for the future of this organic biostimulant, may be its ability to cut down chemical fertilizer without affecting growth. Preliminary research showed that in the presence of the biostimulant, coffee seedlings treated with the half amount of fertilizer yielded the same shoot biomass and higher root biomass than those fully fertilized.
1240 92 - 12/66
Europe, Netherlands, field study, high input agriculture, low external input agriculture, nitrogen cycling, nitrogen balance, nitrogen mineralization, nitrogen immobilization, denitrification, microbial biomass
VAN FASSEN, H.G. and G. LEBBINK
Netherlands J. of Agric. Sc., 38, 1990, pp. 265-282
In this paper, N1-balance calculations covering the growing season will be discussed as well as changes in soil N mineralization rate, in N uptake by the crop, and in N losses due to changes in management. A conventional farming system was compared with two integrated systems, each system with the same rotation of winter wheat, sugar beet, spring barley and potatoes on a silt loam soil. Soil physical conditions and meteorological data necessary to account for some of the differences in overall N budget are discussed.
Field work was carried out at an experimental farm on a calcareous silt loam soil.
A previous experiment at the experimental site, in which three different input regimes of organic matter were compared, was taken as a starting point.
Agroecosystems are inherently more 'leaky' than undisturbed natural ecosystems where vegetation is continuously present. Increased inputs of nitrogen into agriculture have greatly increased crop (N) outputs, but they have also increased N losses to the environment.
Integrated management might give lower crop yields than conventional management, but because of lower costs, the profitability to the farmer could be similar.
Nitrogen balance sheets for the growing seasons of 1986-1988 showed N deficits of 0-170 kg ha-1, suggesting substantial N losses to the environment.
The uncertainty about actual N losses mainly depended on the uncertainty of estimated net N mineralization. Periods with much rainfall in 1987 and 1988, inappropriate use of animal manure and soil compaction may partly account for the heavy N losses in all farming systems. Potential rates of N-cycle processes were studied over the years to observe effects of changes in management.
The following conclusions can be drawn from these studies:
- The uncertainty about actual N losses mainly depended on the uncertainty in the calculated net N mineralization for field conditions. Especially uncertain was the contribution of the layer 40-100 cm, with a rather high organic matter content, to N supply of the crops.
- The soil organic matter and total-N contents showed a tendency to differentiate from their original two levels, into four levels as a result of changes in management. The next years will show which new steady-state levels will eventually result from integrated or conventional management.
- Correlations between N mineralization rates and biomass-N flush of soil samples were found to be situation-dependent.
- On fields with initial organic matter levels of 2.2% and 2.7%, crop yields under integrated management were on average 83% and 88%, respectively, of crop yields under conventional management.
- In the integrated system, the spring application of pig manure had to be changed to autumn application of spent mushroom compost, to prevent N loss by NH3 volatilization and by denitrification. The use of compost is also needed to maintain a high level of soil organic N.
- To minimize the risk of N losses to the environment, soil inorganic N concentrations should be kept low, especially in periods when no active crop is present and N losses are most likely to occur.
1241 92 - 12/67
Review, symposium, rice farming, green manure, cropping systems
Publ. of the International Rice Research Institute, Los Banos, Philippines, 1988, 378 pp., USD 12.30
This book embodies the proceedings of a symposium on sustainable agriculture held in 1987, at the International Rice Research Institute (IRRI), Los Banos, Philippines.
Some 92 scientists from over the world participated in the conference.
Topics include the use of green manures in China, southern Asia, parts of Africa, USA and other areas, as well as topics on woody species, N transformation, soil redox dynamics, and others dealing with general principles.
This book contains a wealth of valuable information on perennial and annual legumes as a N source and for soil improvement in upland and lowland rice production. Basic concepts and practical applications are covered well.
Discussion of N transformation, crop uptake, losses and residual is handled in an thorough manner.
Several of the writers pointed out, the value of green manuring is greater than N supply per se, e.g., several physical and chemical properties are also modified beneficially.
Contributions of N by food-crop grain and food-crop legumes were presented as an important consideration, since the economics of appropriating land and time for N production is often not cost effective due to the cost constraints of labour, land opportunity and seeds. These constraints forced a steep decline in the use of green manures in rice production everywhere as N fertilizer became available and affordable.
The first chapter of the book, nine pages, consists of the recommendations that emerged from the symposium discussions, including research needs and proposed research areas.
Advantages und disadvantages of green manure use are listed.
The papers and discussions during the symposium reconfirmed that - broadly defined - green manure does increase rice yields. Moreover, empirical evidence and theoretical considerations strongly suggest that green manure can contribute to the sustainability of tropical agricultural systems in which rice is a major crop.
The information is presented in 25, generally well-written, edited and documented chapters.
The book is a valuable resource and the information is presented interestingly.
It is an excellent reference to those involved in rice production and possibly a textbook in courses in soil management and sustainable agriculture, especially looking to the future.
1242 92 - 12/68
Africa, Nigeria, humid tropics, field trials, maize, cassava, low-input agriculture, green manure, IRRI
VAN DER HEIDE, J.
In: Green Manure in Rice Farming; Proc. of a Symp. on Sust. Agriculture, IRRI, Philippines, 1988, pp. 186-191
The use of cover crops is particularly relevant in the humid tropics, as high rainfall generally has depleted the soil of nutrients, especially nitrogen, which leaches easily. Levels of soil-organic matter are generally low, and there is a rapid and persisting weed growth, which is one of the main reasons why farmers have to abandon their plots.
Cover crops have been used for a long time by small farmers in the tropics in their crop rotations, mostly as a cheap source of biologically fixed nitrogen, for the recycling of leached nutrients, for protection against erosion, for the build-up and maintenance of soil organic matter and for the suppression of weeds.
Field experiments under humid tropical conditions in southeastern Nigeria for several years studied N requirement and utilization of upland cropping systems, with and without legumes and with low-input management on acid, low-activity clay soils. Total N utilization over several cropping systems was assessed. Quantities of N removed from the soil and left behind as crop residues after harvest and residual effects of N fertilizers and legumes included in the cropping systems were determined.
Although the data presented were obtained in the first years of a long-term experiment, the results indicate that, from the first year after clearing, considerable differences occur in N use and conservation of intercropped or sequentially cropped systems of non-irrigated agriculture in the humid tropics. In three of the four systems studied, more N was removed by harvest products than was returned after harvest with the crop residue, even at the high N fertilizer levels applied in the experiment. This also occurred if pigeonpea or cowpea were included in the cropping system.
A green manure planted after monocropped maize in the second season did not have a significant effect on yield of the following maize crop compared to cowpea, substantially more nitrogen was returned to the plot than was removed by harvest products.
After continuous cropping for 4 yr, the inclusion of a legume in the crop rotation, in particular as a second season cover crop, showed an important residual effect on N supply to monocropped maize. No residual effects were observed from N fertilizer applications.
Cassava utilizes substantial amounts of fertilizer N. Removal of stems from the field after harvest removes large quantities of N from the cropping system. After the basic requirement of cuttings has been satisfied, ways should be found to restore the N in the stems to the soil without harmful side effects. Including a green manure in traditional cropping systems appears to be the best alternative to attain sustained crop production in low-input agriculture, as far as the supply of N is concerned.
Including a green manure crop such as mucuna in the minor season did not result in better performance of maize than of second season cowpea, but did have a pronounced residual effect on the succeeding maize crop.
Detailed studies on the relationship between the inclusion of cover crops and the buildup and maintenance of soil organic matter, and the processes that control the availability of plant nutrients in the low-activity clay soils in the humid tropics are needed.
Since many green manures cannot be used for human consumption, other benefits should become obvious to the farmer after one or two cropping cycles. Grain legumes, although providing immediate economic benefit, tend to accumulate nutrients in the grain which is harvested, so that their effect on the performance of the following crop is usually low.
Nitrogen-fixing cover crops can be an excellent way to supply a substantial quantity of nitrogen and recycled nutrients to the annual crop rotation, by returning the total biomass produced to the soil, just before planting one, or a combination of food crops in the following season. Leguminous forage crops to provide feed for cattle can have a double function.
1243 92 - 12/69
Africa, Rwanda, highlands, acid soils, field trials, beans, wheat, vetch, green manuring, yield, soil fertility, FSRP
YAMOAH, C.F. et al.
Biol. Agric. and Hort., 7, 1991, pp. 303-310
The purpose of this study is to assess the value of vetch used as a green manure crop on acid soil prevalent in the highland region of Rwanda. Bean (Phaseolus vulgaris) and wheat (Triticum aestivum) yields and soil chemical analysis following incorporation of vetch were used to evaluate success in the improvement of soil fertility.
The study was carried out during four cropping seasons.
The soils are classified in the USDA system as Oxisols.
The advantages ascribed to legume green manuring are numerous and include: improvement in soil fertility, increased cation exchange capacity, increased water retention, enhanced microbial activity and improved soil structure.
Vetch (Vicia sativa L.) is a potential green manure crop in the East-Central African highland region where soils are generally acidic.
In this area, vetch grows relatively fast, assumes a quick soil cover to check ground erosion and produces high biomass.
Incorporation of 5-month old vetch lowered soil pH as well as raising exchangeable Al and H and reducing exchangeable Ca, Mg, and P.
Consequently, bean and wheat yields for the subsequent season were reduced by 71 and 33%, respectively. There was no response to fertilizer N on either main treatment. There were no significant yield differences for either crop with respect to vetch treatment during the second season. Third season crop yields were superior on the control plot, with that of beans being significantly different. Application of lime raised exchangeable Ca, K and reduced exchangeable Al. Bean was more affected by exchangeable Al than wheat. Half-life for decomposition of the vetch was 3.5 weeks and nutrient release pattern followed the order: K>N>P>Ca indicating that liming may be required to supply Ca and to neutralize soil acidity at the initial stages of decomposition.
Concluding, it can be stated that in the Rwandan highlands vetch grows rapidly and provides a quick cover to control erosion. Its use for green manuring on the acid soils in this region must be treated with caution.
Decomposing vetch material initially made the soil acidic and crops which immediately followed vetch incorporation suffered severe yield losses. It may be advisable to allow three to four weeks after incorporation before seeding food crops. Similarly, lime application may be necessary to counteract adverse effects of soil acidity during early stages of decomposition and also to supply Ca.
1244 92 - 12/70
Asia, Philippines, humid tropics, lowland, field experiment, cropping systems, preceding crops, organic manure, nitrogen fertilizer, mungbean, sesbania, green manure, rice, maize, yield, residual effects
MEELU, O.P. et al.
Trop. Agric. (Trinidad), 69, 1, 1992, pp. 96-100
This study determined the effects of alternative crops grown late in the dry season on fertilizer N response of wet season irrigated rice and residual effects on dry season irrigated maize.
The experiment was initiated in 1984 on the farm of the International Rice Research Institute, Philippines, and repeated in 1985.
Five cropping sequences were examined:
- Green manure (Sesbania cannabina [Retz] Poir)
- rice (Oryza sativa L.)
- maize (Zea mays L.)
- Fallow [farmyard manure (FYM)] - rice - maize;
- Fallow - rice - maize;
- Mungbean (Vigna radiata [L.] Wilczek) - rice - maize; and
- Maize fodder - rice - maize.
The experiment was laid out in a strip plot design with strips of crops in one direction and strips of N levels in the other. The treatments were replicated four times. Crop sequence and N level strips were re-randomized for each of the four replicates.
The soil of the experimental field was clay.
Mean rice grain yield without fertilizer N was maximum (4.5 t ha 1) after Sesbania and minimum 2.7 t ha-1) after maize fodder. Mean yields of unfertilized rice after FYM, fallow, and mungbean were intermediate, decreasing in that order. Yields of unfertilized rice grown after Sesbania, the aboveground biomass of which accumulated 70 kg N ha-1 (1984) and 98 kg ha-1 (1985) in 60 days were comparable with rice yields in fallow plots to which 44 and 96 kg ha-1 fertilizer N, respectively, were applied. FYM (15 t ha 1) supplied 68 kg N. The efficiency of N from FYM in combination with different N levels on rice ranged 31-51%.
Significant residual effects of FYM and green manure on the succeeding maize crop were not detected. Soil organic C and total N after wet season rice in 1985 were higher when Sesbania and FYM preceded rice compared with maize fodder, mungbean or fallow.
Crops in the tropics are often grown in a particular sequence.
Fertilizers and manures applied to one crop can affect the response of the succeeding crop.
To estimate optimum N fertilizer rates for crops grown in sequence, the effects of the preceding crop species and application of farmyard and green manures should be considered.
1245 92 - 12/71
Africa, Niger, semi-arid tropics, drylands, farm practices, field trials, pearl millet, cowpea, intercropping, soil fertility, crop productivity
REDDY, K.C. et al.
Field Crops Res., 28, 1992, pp. 315-326
The objective of this study was to compare the productivity and effects on soil fertility by rotations of these common crops in Niger.
A 4-year field experiment was conducted in a Psammentic Paleustalf in Niger to determine the continuous cropping effects of pearl millet (Pennisetum glaucum (L) R.Br.), cowpea (Vigna unguiculata (L.) Walp.) and three pearl-millet/cowpea intercrop systems with cowpea planted 1, 2, and 8 weeks after millet planting on soil and crop productivity.
Crops were grown for grain on the same plots under rainfed conditions in 1986, 1987 and 1988 crop seasons and all crop residues were removed from experimental plots.
For three years preceding the experiment, millet was continuously planted in association with cowpea at low densities on these plots, similar to much of the dryland farm practices in Niger.
It can be concluded that millet/cowpea intercrop systems showed better land-use efficiency than sole millet or cowpea systems. On a total grain-yield basis, sole cowpea was more productive. Continuous cropping of sole cowpea with residue removal significantly increased soil Mg and OM over sole millet or millet/cowpea intercrops. Test-crop millet produced significantly higher dry-matter yield and N uptake in PCS sole cowpea than other treatments. Test-crop millet N uptake after previous intercrop treatments was significantly greater than previous sole millet. This leads us to believe that cowpea inclusion in sole or intercrop systems would make extra soil N available to following cereal crops such as millet. From a practical point of view, introduction of sole cowpea or cowpea-based intercrop systems in place of traditional millet-dominated intercrop systems may be advantageous.
Pearl millet (Pennisetum glaucum (L.) R.Br.) is planted principally for grain on about 10 million ha in West Africa. Generally in this region, millet is grown on infertile sandy soils in association with cereals such as sorghum and/or with legumes such as cowpea or groundnuts. Of all the combinations, the millet/cowpea association is the most widely used in the Sahelian zone of Niger, extending up to 50% of the country's cultivated area (about 2 million ha).
In recent years, farmers in Niger and other West African countries increased land area under millet cultivation to meet food needs by effectively decreasing the fallow period or replacing the traditional shifting cultivation with continuous cropping of millet-dominated intercrop systems.
As the application of fertilizers is not always economical in the semi-arid tropics of Niger, non-fertilizer-based methods to improve soil conditions, such as legume use, deserve special attention. In spite of a tremendous knowledge base in this area from Asian and Western countries, crop rotation on the impoverished soils of West Africa is not practiced.
This and other improper cultural practices are leading to a large-scale degradation of soils in this area.
1246 92 - 12/72
Latin America, Colombia, field trial, phosphorus availability, bean seed tolerance, seedlings, mineral deficiences, roots, leaves, stems, starch, content, protein content, CIAT
Tesis Universidad Nacional de Colombia, Bogota, Colombia; Ing. Agr. Palmira: 1991, 81 pp.
The influence of certain quantitative characteristics of bean seed on the capacity of seedlings to tolerate low available P in the soil was determined. The starch, protein, phytic acid, and different P fractions of the seed were determined in 23 bean genotypes during the 1th phase of research. Results indicated that the reduction in total biomass production of the seedling and in tissue P concentration was pronounced at 16 days after planting, as a direct consequence of soil P deficiency.
However, this reduction was more pronounced in the leaves since a greater amount of photosynthates were invested in root production, thus increasing the relative extension of the root system in the soil. The no. of main roots proved to be a variety characteristic that is unmodified by soil P levels. On the other hand, the size of endodermical cells was significantly increased by the low P treatment, possibly due to a nutritional physiological adaptation mechanism; however, no significant differences were found among variety. Seed weight and size of cotyledon cells showed a positive, highly significant correlation with seedling vigor. The coefficients of correlation obtained in the low P treatment were higher than those of the high P treatment, indicating that the nutritional dependence of the seedlings is more pronounced under P deficiency conditions. Variance analysis showed that cotyledon reserves satisfied the nutritional needs of the seedlings more less up to 12 days after planting, after which significant differences in growth rates occurred. Although total biomass production was directly related to seed size, it did not affect the duration of reserves. Although the experiments attempted to minimize the variations existing between environments (pots and tubes) and between replications, statistical analysis revealed significant differences due to these factors. Root analysis in modified PVC tubes was useful in the study of overall genotype performance, but maladjustments occurred that affected the final results of P treatment.
1247 92 - 12/73
Asia, India, field trial, legumes, arid areas, phosphate application, soil nitrogen, pearl millet
KATHJU, S. et al.
Trop. Agric. (Trinidad), 64, 2, 1987, 91-96
Low organic matter and low N in most soils of arid and semi-arid parts of Rajasthan present the opportunity for the adoption of a low-input approach towards improvement of fertility through the cultivation of legumes. It is also felt that soil N, thus augmented, might contribute much towards the yield improvements of subsequent cereal crops, particularly of pearl millet, grown extensively in these parts. In this regard, the importance of phosphate fertilization to legumes for the improvement of their performance and N2 fixation has been documented in a number of reports. Although mungbean, moth bean and clusterbean are widely cultivated in these parts, there seems to be little knowledge regarding the effects of phosphate fertilization on these legumes and succeeding cereal crops. Such an assessment, moreover, is particularly needed because of the uncertainty of monsoonal rains and the drought-prone nature of the region; the effects of P on the growth, yield and water-use of legumes in different rainfall situations assume importance. Again, the implication of P application on soil N enrichment and the consequent yield improvement of the succeeding cereal crop warrant special consideration in view of the reports of beneficial effects of P on soil N status, even in situations where the performance of the legumes was not influenced. This paper relates some findings in these areas.
Mungbean (Vigna radiata), moth bean (Phaseolus acontifolius) and clusterbean (Cyamopsis tetragonoloba), grown over three successive years under low and variable rainfall on loamy sand soils of arid western Rajasthan, did not reveal any marked effect of phosphate application (0, 20, 40, 60 and 80 kg P2O5ha-1) on the consumptive use of moisture. The effects on dry matter production and seed yield were marginal, but not significant. Uniform distribution of precipitation during the growing period, rather than its quantum, had the more favourable influence on plants. P application induced a small increase in the available P status of the soil and also in N and P uptake. But the weight of nodules per plant and root CEC progressively increased with increasing level of P up to 40-60 kg P2O5ha-1. Phosphate application also led to an increase in soil N, particularly of the hydrolyzable organic-N fraction. Effects on mineralized N were marginal. The amount of N2 fixed was greater in mungbean and moth bean than in clusterbean but the mineralized and hydrolyzable organic-N fractions increased more under clusterbean. While the phosphate levels did not have any effect on the succeeding pearl millet (Pennisetum typhoides) crop, the legumes significantly promoted its yield equivalent to > 80 kg N ha-1, despite the prevalence of acute drought conditions. The beneficial effect of clusterbean was found to be greatest, followed by moth bean and mungbean. It seems that the beneficial effect of legume cultivation arose not only from the total N2 fixed but also from the level of mineralized and hydrolyzable organic N contributed by plant residues left in the soil.
1248 92 - 12/74
Asia, India, dryland agriculture, field trial, clay loam soil, cropping systems, fertilizer, pigeonpea, sorghum, sole cropping, intercropping
PANDEY, R.C. et al.
IPN, 15, 1992, pp. 12-15
This paper attempts to identify nutrient management in sole and intercropping systems which improves the soil environment and maximizes productivity on a sustained basis.
Three cropping systems, sole pigeonpea, sole sorghum, and pigeonpea intercropped with sorghum (1:2) were tested under two sets of fertilizer regions.
The sustainable yield index (SYI) and the sustainable value index (SVI) were computed to analyze the comparative performance of sole and intercropping systems with respect to fertilizer use.
The data indicate among others that sole pigeonpea gave maximum pigeonpea seed equivalent yield followed by pigeonpea + sorghum intercropping at all levels of N under study. Enhancing the application of nitrogen from 15 to 60 kg ha-1 increased the yield by 40% for sole pigeonpea and sole sorghum, and by 54% for pigeonpea + sorghum intercropping system in terms of pigeonpea seed equivalent over the lowest dose. This showed that an intercrop of pigeonpea + sorghum was beneficial and efficient compared to sole cropping in respect of nitrogen uptake. The maximum LER (1.24) was obtained in pigeonpea + sorghum intercropping system at 60 kg N ha-1.
The superiority of intercropping over sole cropping in terms of insurance from risk, better resource use, and higher return has been highlighted by many workers. But sustainable fertilizer management in an intercropping system is not yet well understood. Under dryland situations, land, water, and crop management systems which guarantee sustained production and productivity over a wide range of environments or over many years in the same location would qualify to be called sustainable agricultural systems.
1249 92 - 12/75
Review, book, humid tropics, acid upland soils, Oxisols, Ultisols, plant nutrients, organic matter, soil management systems, fertilizer, crop production, FAO
VON UEXKULL, H.R.
FAO Fertilizer and Plant Nutrition Bulletin, 10, ISBN 92-5-102387-5,
1986, 51 pp. + references
The largest reserves of potential arable land still available in the world are located in the humid tropics.
Significant advances have been made in the characterisation and management of acid soils in the uplands of the humid tropics. The aim of this bulletin is to review the experience already acquired and to summarise the research findings which have recently become available.
On the uplands, acid soils predominate and agriculture at a low level of inputs is only possible through shifting cultivation, in which the land is cropped for a few years in alternation with long periods of fallow.
In most cases crop growth in acid soils can be directly correlated with Al saturation or Al concentration in the soil solution. High H+ concentrations in the soil solution, however, favour weathering of soil minerals, resulting in the release of Al3+ and the leaching of ions such as K+, Mg2+, Ca2+ and Mn2+.
Poor crop growth on acid soils is usually caused by aluminium and/or manganese toxicity and/or by deficiencies of phosphorus, calcium and magnesium.
Most of these soils are at present under virgin rain forest, with smaller areas under savanna, tree crops and shifting cultivation. The main reason for lack of development of these soils is that a high standard of management and costly inputs are needed to bring them into permanent arable cropping.
Most of the acid upland soils of the humid tropics are classified as Oxisols (Ferrasols) and Ultisols (Acrisols). Both groups are very acid with low base status, their mineral horizons containing small amounts of most nutrients.
When cropped without proper management, most acid soils of the humid tropics deteriorate, chemically and physically, so quickly after clearing that after a few years no crop can be grown on them. With adequate inputs and proper care, the annual productivity of these soils can far exceed the productivity of most fertile soils in temperate regions.
Where population pressure is low, shifting cultivation is often still the most appropriate land use system.
Better techniques of forest clearing are being developed. Zero-burn techniques in which the felled forest biomass is broken down under a short term leguminous cover crop followed by moderate applications of lime and P fertilizer show considerable promise.
Three levels of intensity can be distinguished and are discussed in this book:
- shifting cultivation with no lime or fertilizer inputs, relying on long fallow periods for regeneration;
- continuous cultivation with moderate applications of lime and P fertilizer, using leguminous cover crops or alley crops to provide biologically fixed nitrogen and organic matter;
- intensive continous cropping with large and continued inputs of NPK fertilizer, lime and other nutrients, a system that is capable of reaching and maintaining very high levels of productivity.
With good management once infertile acid tropical soils can produce annually the equivalent of 15 to 20 t/ha of grain. The availability of high yielding and disease resistant cultivars means that maize yields in excess of 10 t/ha per crop are now obtainable, while acid tolerant and disease resistant soybean cultivars can yield 2.5 to 3 t/ha per crop. It will usually take several years of good management to achieve these yield levels.
High rates of fertilizer are recommended by the author to maintain production when three crops are taken.
The rates are very similar to the rates used by many temperate region farmers aiming for comparable yields.
When high inputs are used the risks involved must be minimised. For acid upland soils this can only be done by conserving organic matter.
Organic matter, lime, and P are the three main factors on which a successful soil management and crop productivity programme for acid tropical soils can be built.
The agronomic practices adopted must supply a correct balance of organic manure and additional mineral fertilizer.
1250 92 - 12/76
Review, book, Latin America, Colombia, CIAT, mycorrhiza management, agronomic importance, cropping systems, practical technologies
Publ. of GTZ, 6236 Eschborn, Postf. 5180, Germany, ISBN 3-88085-462-9, 1991, 371 pp., pbk
Increasing crop production and land productivity in the tropics is essential if the food demand of the growing population in these areas is to be met. Of all the soil-related constraints on crop production, low soil fertility is the most severe on more than half of the arable land in the tropics. Infertile soils are acidic and may be deficient in phosphorus, nitrogen and potassium. On these soils crop production can only be improved when fertilizers, in either organic or inorganic form, are applied, and when soil amendments are combined with improved crop production technologies. This is explained by Ewald Sieverding in his book Vesicular-Arbuscular Mycorrhiza Management, in which he describes the role these fungi can play in improving soil fertility.
The author explains that until about 20 years ago, vesicular-arbuscular mycorrhizal (VAM) fungi were virtually ignored by most soil and plant scientists. However, under controlled greenhouse conditions it has been demonstrated that VAM fungi increase phosphorus uptake. They also play a role in the uptake of other plant nutrients as well as in the biological nitrogen fixation of Rhizobium, the biological control of root pathogens, and the drought resistance of plants.
In 1980 a Mycorrhiza Special Project was initiated at the Centro Internacional de Agricultura Tropical (CIAT), in Cali, Colombia. The general objectives of this project were to test the agronomic importance of VAM in tropical crop production systems and to develop practical technologies to utilize VAM fungi as a biological resource to enhance phosphorus uptake and utilization.
Although the content of this book relates directly to South America, with particular reference to cassava, the principles of the VAM technology presented can be transferred to other crops and to conditions in tropical Africa and Asia, provided that the technology is adapted to the prevailing ecological and socio-economic conditions.
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Germany, study, greenhouse conditions, mycorrhiza, pigeonpea, phosphorus fertilizer, plant growth
Publ. of the Institute of Agronomy in the Tropics, Univ. Gttingen, Germany. Presented at the Int. Symposium on Management of Mycorrhiza in Agric., Hortic. and Forestry, Perth, Australia, 1992
The aim of the present paper revolves around the following questions: Are there differences between various VA mycorrhizal fungi in improving P uptake from different P sources with varying solubility? Do different P fertilizers exert an effect on the interaction of VA mycorrhiza and rhizobium? Does pigeon pea take advantage of a dual symbiosis?
The contribution of legumes in tropical cropping systems to maintain/restore soil fertility is gaining increasing importance. The most important aspect of tropical legumes is their ability to fix P in association with rhizobium atmospheric dinitrogen which becomes available to subsequent crops in rotational cropping systems. This is true for pigeon pea (Cajanus cajan) which fits into many agronomic management systems because of its multipurpose use. However, unfavorable soil conditions in the tropics often impede development of pigeon pea and phosphorous is considered to be the most limiting factor. Studies indicate the need for application of between 20-100 kg/ha of phosphorus.
This, however, is a luxury most farmers in the tropics with very limited financial resources can ill-afford. Consequently, seeking other possibilities to overcome this problem deserves special attention. In this context, the management of effective VA mycorrhizal fungi could become a promising tool to increase the efficiency of applied P fertilizers and thus reducing financial expenses.
The present research work was conducted under greenhouse conditions using a non-sterilized P fixing soil. Three P sources were applied at the following rates (kg P/ha): single superphosphate 10, 30, 60; and two rock phosphated from Brazil; Patos de Minas (total P, 10.7%): 50, 150, 300; and Arax (total P, 12.1%): 50, 150, 300. The soil contained 2 native species of Glomales: Glomus albidum and Glomus intraradix. The mycorrhizal inoculum consisted of an air-dried mixture of soil/roots/spores and was applied at the rate of 2g/pot. Four VAM species originating from the Cerrado Ecosystem of Brazil were tested:
Glomus clarum, Glomus pallidum, Entrophospora colombiana, Acaulospora rehmii and Glomus manihotis from CIAT/Colombia (C-1-1). Cajanus cajan plants were not fertilized with N but inoculated with a peat-based inoculum of effective strains of rhizobium also from the Cerrado region.
The present results clearly indicate a strong dependency of pigeonpea on VAM fungi under P stress and Glomus clarum proved to be the most effective fungus irrespective of the P source and P level. In general, mycorrhizal infection rate was not influenced by the P source. However, with the exception of Glomus clarum, infection rate tended to decrease with increasing P levels. P uptake of inoculated plants corresponded well with the plant development and a similar tendency was observed with N uptake. With inoculated plants a significant relationship between P uptake/nodule formation and nodule formation/shoot dry weight was found, in particular with rock phosphate (Araxs). This relationship decreased with increasing solubility of the P source. The present results bear evidence that the fertilizer efficiency of low grade rock phosphates is dependent on an effective VA mycorrhiza. With Cajanus cajan an additive interaction of effective VA mycorrhiza and rhizobium was observed resulting in: improved P and N uptake, increased nodule formation and, enhanced plant growth.
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USA, study, greenhouse experiment, sorghum, genotypes, mycorrhiza, phosphorus efficiency, cost/benefit analysis
RAJU, P.S. et al.
Plant and Soil, 124, 1990, pp. 199-204
This study was conducted to determine benefit and cost analysis and P efficiency (dry matter produced/unit P absorbed) of Glomus fasciculatum colonization with sorghum roots when genotypes were grown at different soil P levels.
Sorghum [Sorghum bicolor (L.) Moench] was grown in a greenhouse in a low P (3.6 mgkg-1) soil inoculated with the vesicular-arbuscular mycorrhizal fungi (VMAF) Glomus fasciculatum and P added at 0, 12.5, 25.0, and 37.5 mgkg-1 soil to determine the effects of VAMF-root associations on plant growth, and P efficiency (dry matter produced/unit P absorbed).
Root associations with vesicular-arbuscular mycorrhizal fungi (VAMF) normally benefit plant growth, particularly through enhanced P uptake.
Host plants must provide carbohydrates to VAMF for development and growth.
In this study root colonization with VAMF and shoot growth enhancements decreased with increased soil P applications. Mycorrhizal plants were less P efficient than nonmycorrhizal plants. Shoot dry matter differences between mycorrhizal and nonmycorrhizal plants were considered the benefit derived by plants from VAMF-root associations.
Shoot dry matter differences between mycorrhizal and nonmycorrhizal plants with similar P concentrations were considered the costs paid by plants for VAMF-root associations. Values of benefit and cost analysis for VAMF-root associations were highest when soil P was lowest and decreased with increasing P applications. Genotypic differences for calculated costs were pronounced, but not benefits. Benefit and cost analysis may be helpful to evaluate host plant genotypes and VAMF species to optimize efficiencies of VAMF symbiosis in different soil environments.
VAMF associations with plant roots not only benefit growth and mineral element uptake, but VAMF infected plants can give greater tolerance to root pathogens, drought, low soil temperatures, adverse soil pH, and transplant shock. VAMF-root associations have great potential in land reclamation and agriculture practices on arid and acid lands, where drought, low soil fertility (especially P deficiency), and high soil salinity and/or toxicity elements can be major constraints to crop production.