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Use of Radioactive 32p Technique to Study Phosphate Rock Dissolution in Acid Soils
(2002) G.L. Mullins; Sen H. Chien; Mahisarakul, J.
A laboratory experiment was conducted to evaluate the dissolution of six sources of phosphate rock in two acid soils (Ultisols): a sandy soil and a red clay soil. Labile P was determined using the radioactive 32P technique for Pi extractable P and resin extractable P. Incubations were conducted for 0, 1, 2, 3, 4 and 5 weeks for 32P exchangeable technique, 0 and 5 weeks for Pi technique and 5 weeks for resin technique. Rates of PR were 0 and 400 mgP/ha. The results showed that labile P in the sandy soil decreased from 0-1 weeks for all the PRs except Hahotoe PR and Hazara PR's. Between 1 and 5 weeks labile P remained relatively constant. The ranking of labile P from PRs was: North Carolina = Kouribga > Matam > Hahotoe = Hazara> Patos de Minas. In the red soil, labile P from all PRs appeared to be relatively unchanged during the 0-5 week incubation. Pi extractable P in sandy soil showed no significant differences due to incubation time. In the red clay soil, there was a significant decrease in Pi-P extracted from soil mixtures with PRs after 5 weeks as compared to 0 weeks. Results of the Resin-extractable P in both sandy and red soils were in agreement with labile P as measured by 32P exchange technique.
Water Productivity and Potato Cultivation
(2003) Walter Truman Bowen
This chapter provides a review of work done at the International Potato Center (CIP) on improving water productivity in potato. Generally, potato is shallow-rooted and sensitive to even mild water deficits. Most of CIP’s work related to water productivity was done in the 1980s as part of a research programme to develop improved germplasm and agronomic practices for potato production in warm tropical environments. Heat-tolerant as well as drought-tolerant materials were selected and tested under a range of warm climates, with studies conducted to quantify evapotranspiration, stomatal conductance, leaf water potential, soil water dynamics and root growth. These same parameters were also determined in agronomic field experiments designed to quantify the effects of mulching, intercropping and close plant spacing on yield and water-use efficiency. Although needed, similar detailed studies on water-productivity components have yet to be done for potato grown more commonly in cooler environments at high altitudes in the tropics.
World Phosphate Deposits
(2004) McClellan, G.H.; Van Kauwenbergh, S.J.
This chapter delves into the global distribution, production, consumption, reserves, and future trends of phosphate rock (PR). PR, encompassing both unbeneficiated ores and concentrated products, primarily originates from sedimentary and igneous deposits. Sedimentary deposits, notably prevalent in Morocco, the United States, and China, constitute the majority of global production, with sedimentary francolite deposits being highly reactive for direct agricultural application. Igneous deposits, although less abundant, are found in various countries but typically contain less reactive fluorapatite. The chapter outlines world PR production, highlighting major producers and indicating a decline in direct application phosphate rock (DAPR) consumption over the years. Additionally, it examines global PR reserves and resources, emphasizing regional disparities and estimating potential resources suitable for direct application. Future trends suggest potential growth in production from certain regions and the possibility of discovering new deposits, including offshore reserves.
Soil Testing for Phosphate Rock Application
(2004) Sen H. Chien
Soil testing for phosphorus (P) has been a subject for extensive research. Numerous extractants ranging from strong acids to alkalis and various organic and inorganic complexing agents have been developed to evaluate P bioavailability with certain crops and soils. The most widely used soil P tests are Bray I (Bray and Kurtz, 1945), Mehlich I (Nelson et al., 1953), and Olsen (Olsen et al., 1954). Other common tests include Bray II, Mehlich II and III, and resin (Fixen and Grove, 1990). However, all these soil tests are mainly for recommendations with water-soluble P fertilizers such as di-ammonium phosphate (DAP), single superphosphate (SSP) and triple superphosphate (TSP). Reports have shown that these conventional acid or alkaline soil tests do not work well in soils fertilized with phosphate rock (PR) (Perrott et al., 1993; Menon and Chien, 1995; Rajan et al., 1996). Thus, there is a need to develop appropriate soil tests that reflect closely P uptake from PR over a wide range of PR sources, soil properties, and crop varieties. Furthermore, the soil tests should be suitable for PR and for water-soluble P fertilizers. This issue has become more important because of the increasing interest in the use of PR for direct application in developed and developing countries, e.g. Australia, New Zealand, Brazil, Indonesia, Malaysia and countries in sub-Saharan Africa. This chapter provides an overview of the soil tests that have been used to measure available P from soils treated with PR and water-soluble P fertilizer. It provides an introduction to the nature of the reactions of PR and water-soluble P fertilizer in soils. It then discusses the use of the 32P isotopic exchange kinetic method in relation to soil-available P measurement.
Legislation and Quality Control of Phosphate Rocks for Direct Application
(2004) Sen H. Chien
Legislation plays a crucial role in ensuring the quality and safety of phosphate rocks (PR) used for direct application as fertilizers. This chapter reviews the existing legislation in various countries regarding PR for direct application, focusing on total P2O5 content, solubility, and particle size. Examples from countries like Malaysia, Brazil, India, and New Zealand are discussed. Issues associated with legislation, such as the relevance of total P2O5 content to agronomic effectiveness and the effects of solubility, particle size, and free carbonates on PR reactivity, are explored. Guidelines for legislation on PR for direct application are proposed, emphasizing the importance of considering agronomic effectiveness, solubility measurement methods, particle size requirements, and other factors affecting PR quality.
Soil Phosphorus Dynamics, Acquisition and Cycling in Crop–Pasture–Fallow Systems in Low Fertility Tropical Soils: A Review from Latin America
(2004) I.M. Rao; E. Barrios; E. Amézquita; Dennis K. Friesen; R. Thomas; Astrid Oberson; B.R. Singh
Knowledge of the phosphorus (P) dynamics in the soil–plant system, and especially of the short- and long-term fate of P fertiliser in relation to different management practices, is essential for the sustainable management of tropical agroecosystems. A series of field trials was conducted in the tropical savannas and Andean hillsides in Colombia to follow the dynamics of P under different management systems. In tropical savannas in the Llanos of Colombia, in cereal–legume rotations (maize–soybean or rice–cowpea) and ley pasture systems, measurements of soil P fractions indicated that applied P moves preferentially into labile inorganic P pools, and then only slowly via biomass production and microbes into organic P pools under both introduced pastures and crop rotations. Field studies conducted to quantify the residual effectiveness of P fertiliser inputs in crop rotations in terms of both crop growth response and labile P pool sizes, indicated that soluble P applications to oxisols of Colombia remain available for periods that are much longer than expected for ‘high P-fixing’ soils, such as the oxisols of Brazilian Cerrados. In Andean hillsides of Colombia, the impact of short-term planted fallows to restore soil fertility in N and P-deficient soils by enhancing nutrient recycling through the provision of organic matter, was investigated. Results indicated that the fractionation of soil organic matter and soil P could be more effective for detecting the impact of planted fallows on improving soil fertility than the conventional soil analysis methods. Litterbag field studies contributed to characterisation of the rate of decomposition and nutrient release from green manures and organic materials that could serve as biofertilisers. The data sets from these field and greenhouse studies are valuable for further testing and validation of APSIM.
Secondary Nutrients, Micronutrients, Liming Effect and Hazardous Elements Associated with Phosphate Rock Use
(2004) Sen H. Chien
Phosphate rock (PR) is recommended for application to acid soils where phosphorus (P) is an important limiting nutrient on plant growth. The past 50 years have seen the accumulation of considerable knowledge regarding the factors affecting the agronomic effectiveness of PR for direct application. However, much less information is available on other effects associated with PR use, i.e. secondary nutrients, micronutrients, liming effect, and hazardous elements. This chapter presents a review of the information available in literature that is relevant to these other effects.
Economic Factors in the Adoption and Utilization of Phosphate Rocks
(2004) Kuyvenhoven, A.; Sen H. Chien; E. Casanova
The degradation of soil fertility due to increased population pressure, reduced fallow periods, deforestation, and improper agricultural practices poses a significant challenge to sustainable agriculture in many developing regions. Phosphorus (P) deficiency, in particular, has emerged as a critical issue, threatening agricultural viability and food security. This paper examines the economic factors influencing the adoption and utilization of phosphate rocks (PR) as a means to address soil fertility depletion. Constraints such as limited financial resources, poor distribution systems, lack of knowledge about PR utilization, and dependence on fertilizer aid hinder widespread adoption. Additionally, factors such as ownership rights, farm size, access to credit, and labor availability influence farmers' decisions regarding PR adoption. While PR application offers potential benefits in terms of soil fertility improvement and long-term agricultural productivity, challenges related to production costs, transport, and distribution must be addressed. Policy interventions such as pricing policies, organizational support, agricultural market development, and risk protection measures are crucial to incentivize PR adoption and promote sustainable agriculture.
Characterization of Phosphate Rocks
(2004) Van Kauwenbergh, S.J.; McClellan, G.H.
Characterization studies of phosphate rock (PR) samples should provide data on: (i) the composition of the apatite, other phosphate minerals and gangue minerals; (ii) the relative amounts of mineral species present (estimated); and (iii) the particle size of the various minerals in the rock fabric, etc. It is possible to combine this information with a comprehensive chemical analysis to determine the distribution of chemical species among the mineral components. Based on such an evaluation, it is possible to estimate the potential for beneficiation, suggest possible beneficiation routes, and make a preliminary assessment of the suitability of PRs for various fertilizer production processes and/or their applicability for direct application.
Improving Phosphorus Fertility in Tropical Soils through Biological Interventions
(2005-06-30) Astrid Oberson; Else K. Bunemann; Dennis K. Friesen; I.M. Rao; Paul C. Smithson; Benjamin L. Turner; Emmanuel Frossard
Phosphorus availability is a critical factor limiting agricultural productivity in highly weathered tropical soils. These soils often have a high capacity to adsorb phosphorus, making it less available to plants, both from soil reserves and added fertilizers. In such environments, biological processes play a vital role in enhancing phosphorus availability to crops. Soil microbes mediate the turnover of organic phosphorus and organic amendments, preventing strong sorption of phosphorus and maintaining it in a plant-accessible form. However, these microbial processes are contingent on the availability of decomposable organic carbon. This chapter explores various strategies to enhance soil biological activity and, consequently, improve soil phosphorus availability, with a focus on case studies from Colombia and Kenya. It also discusses the challenges and complexities of synchronizing nutrient release by microbial processes with plant demand.
Restoring Soil Fertility in Semi-Arid West Africa: Assessment of an Indigenous Technology
(2006) Abdoulaye Mando; Dougbedji Fatondji; Robert Zougmore ; Lijbert Brussaard; Charles Bielders; Christopher Martius
Low soil fertility and surface sealing, leading to severe water loss through runoff and to a drastic decline in vegetation cover, are major Sahelian agricultural constraints (Casenave and Valentin, 1989; Bationo and Mokwunye, 1991). Owing to lack of ﬁnancial resources it is often not possible for farmers to utilize external inputs to solve these problems. Increasingly, attention has focused on low-cost but effective alternative solutions. Given the region’s poverty, new innovations will only get adopted if they are cheap, easily accessible, and minimize the use of external inputs. Further, the chances for adoption will be higher if the proposed technology is based on some improvement of traditional practices.
Intensity Cultivation Induced Effects on Soil Organic Carbon Dynamic in the Western Cotton Area of Burkina Faso
(2006-10-13) Badiori Ouattara; Korodjouma Ouattara; Georges Serpantie; Abdoulaye Mando ; Michel P. Sedogo; Andre Bationo
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 lm. 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 lm) 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.
Fertilizers and Food Production
(2007) Amit H. Roy
Fertilizers provide plants with the nutrients they need for their growth and development. Plants live, grow, and reproduce by taking up water and nutrients, carbon dioxide from the air, and energy from the sun. Apart from carbon, hydrogen, and oxygen, which collectively make up 90–95 percent of the dry matter of all plants, other nutrients needed by plants come essentially from the media in which they grow—essentially in the soil. The other nutrients are subdivided into primary nutrients (nitrogen, phosphorus, and potassium) and secondary nutrients (calcium, magnesium, and sulfur). In addition, plants also need other nutrients in much smaller amounts, and they are referred to as micro-nutrients (boron, chlorine, copper, iron, manganese, molybdenum, and zinc).
The Lesson of Drente's 'Essen' Soil Nutrient Depletion in Sub-Saharan Africa and Management Strategies for Soil Replenishment
(2008-02) Henk Breman; Bidjokazo Fofana; Abdoulaye Mando
The term "replenishment" is used in a misleading way when it is suggested that soils are poor through depletion by farmers and that soils should be restored to their original state for agricultural development. This philosophy created awareness for problems confronted by African farmers. It neglects, however, the heterogeneous redistribution of nutrients that is inherent to agricultural land use. Active and passive transport of organic matter causes centripetal concentration of nutrients around farms and villages and maintains or even improves the soil fertility of crucial fields at the cost of surrounding land. The advice to use fertilizers on bush fields in view of the use of compost and manure on compound fields is like “putting the cart before the horse”; the value: cost ratio of using inorganic fertilizer on compound fields is higher than that on bush fields given their negative organic matter and nutrient balances. The integrated use of inorganic fertilizers and organic forms of manure triggers a positive spiral of improved nutrient use efficiency and improved soil organic matter status. The increasing value: cost ratio of fertilizer use improves the access to this and other external inputs. Where crop-livestock integration is an important component of the intensifying production system, the centripetal concentration (see footnote 1) can even turn into the opposite, a centrifugal transport that replenishes (planned or unplanned) the depleted surroundings of farms and villages. Active replenishment of depleted soils is no requirement for agricultural development; intensification can start on village fields where fertility is maintained or improved. However, public investment in soils, focusing on reinforcement of the positive effects of the centripetal concentration of organic matter and nutrients, is recommended; it enables farmers to start fertilizer use where even the compound fields at present do not allow it.
Fertilizer in Kenya: Factors Driving the Increase in Usage by Smallholder Farmers
(2011) Joshua Ariga; Thomas S. Jayne
This chapter provides an overview of the factors driving the increase in fertilizer usage by smallholder farmers in Kenya, focusing on policy reforms and market dynamics. The narrative contrasts the historical context of state intervention in agriculture with the liberalization policies of the 1990s and their impact on fertilizer markets and maize production. It highlights the role of market infrastructure, government subsidies, and private sector involvement in shaping fertilizer access and usage. The analysis is based on data from household surveys and government reports covering the period from the late 1980s to the early 2010s.
Save and Growth: Soil Health
(2011) Amit H. Roy
This chapter delves into the critical aspect of soil health in agriculture, emphasizing the imperative for a return to foundational principles. It advocates for a paradigm shift towards recognizing and prioritizing the vitality of soil, highlighting its pivotal role in sustainable agricultural practices. By tapping into natural reservoirs of plant nutrition and exercising prudence in the application of mineral fertilizers, this chapter underscores the essence of fostering healthy soil ecosystems. Through a holistic approach that honors the intricate balance of nature, it endeavors to guide agricultural practices towards resilience, productivity, and long-term viability.
Estimating DSSAT Cropping System Cultivator-Specific Parameters Using Bayesian Techniques
(2011-01) James W. Jones; Jianqiang He; Kenneth J. Boote; Paul W. Wilkens ; Cheryl H. Porter; Z. Hu
Crop models are highly useful for simulating crop and soil processes in response to variations in climate and management. However, if one wishes to simulate a crop's performance in a specific soil and climate for a particular set of management inputs, cultivar-specific parameters (CSPs) are needed because of the genetic variations among cultivars of any crop. In this chapter, we summarized methods that have been used to estimate CSPs for the CERES and CROPGRO-based models in the Decision Support System for Agrotechnology Transfer (DSSAT) cropping system model. We primarily described a Bayesian parameter estimation procedure (the Generalized Likelihood Uncertainty Estimation, or GLUE) for use in estimating CSPs in DSSAT. The procedure is simple to use, requiring only that users select a crop, a cultivar, and the data for use in the estimation procedure from a list of data available for that cultivar in the DSSAT system. Results are displayed for users to view and copy to the standard cultivar file in DSSAT for the crop involved. The procedure does require a large number of model runs; we recommend 6000 but users can optionally change this number. Two cultivars, ‘Prisma’ maize (Zea mays L.) and ‘Williams’ soybean [Glycine max (L.) Merr.] were selected to demonstrate the performance of DSSAT GLUE program. For Prisma maize, two experiments conducted in Zaragosa, Spain in 1995 and 1996 were selected; for Williams soybean, three experiments individually conducted in Wooster, OH and Gainesville, FL, were selected for the demonstration. Results showed that the GLUE method performed better than the arbitrary default CSPs and slightly better than the hand-calibrated CSPs in simulating these maize and soybean cultivars when using one time measurements, such as phenology dates, final dry matter yield, maximum leaf area index, and grain yield. For example, in the Prisma maize experiments in Zaragosa, Spain in 1995 and 1996, the average relative absolute error (RAE) values between the simulated and measured output variables were only 3 and 8%, respectively, while they were between 4 and 10% for hand-calibrated CSPs and above 16% for the default CSPs.
Impact of Bt Cotton, the Potential Future Benefits from Biotechnology in China and India
(2011-07) Carl E. Pray; Latha Nagarajan; Jikun Huang; Ruifa Hu; Bharat Ramaswami
Early studies of Bt cotton’s impacts in China and India found increases in yield per hectare, especially in India, and major reductions in pesticide use, especially in China which led to positive health impacts. In recent years, little has been published on impacts of GM crops, leading to the question: have Chinese and Indian farmers continued to benefit? This paper assesses findings of recent publications on this topic and presents new, unpublished data to answer this question and to examine potential benefit from several new GM crops. The promise of major benefits of Bt cotton identified in early studies has proven true. Bt cotton has spread to all areas of China and India where bollworm is a problem. Bt cotton continues to control bollworm in both countries, and farmers continue as major beneficiaries rather than biotech or seed companies. In China, evidence also suggests that Bt cotton has suppressed the bollworm population so that growers and producers of other crops also susceptible to bollworm are benefitting. This paper also finds that Bt rice and Bt eggplant could have major positive impacts― increasing farmers’ profits by reducing pesticide use and reducing farmers’ exposure to chemical pesticides. Both crops were approved for commercial production by government biosafety regulators, but adoption of GM eggplant has been held up by the Indian Minister of the Environment while specific Bt rice hybrids are still being evaluated by the Chinese Ministry of Agriculture.
Promoting Sustainable Crop-Livestock Integration Through Farmer’s Participation and Integrated Soil Fertility Management in the Sahel of West Africa
(2012) Bidjokazo Fofana; Zacharie Zida; Guillaume Ezui
The Sahelian region of West Africa faces challenges in sustainable agriculture due to low and variable rainfall, leading to declining soil fertility and limited livestock feed resources. This study focuses on integrated soil fertility management (ISFM) and participatory approaches to improve crop-livestock integration for sustainable agricultural systems in the Sahel. Field experiments and participatory rural appraisals were conducted in Burkina Faso to assess farmers' knowledge of soil fertility management, understand traditional practices, and identify solutions for sustainable mixed crop-livestock systems. Results indicate spatial variability in soil fertility between infield and outfield sites, with infields being more fertile due to continuous application of organic amendments. Livestock ownership correlates with manure availability, impacting crop production. Participatory approaches revealed farmers' reliance on rainfall and nutrient deficiencies as major constraints, with proposed solutions including manure and compost use, and improved crop rotations. Modeling with SIMFIS (SImulating Mixed Farming In the Sahel) provided insights into management alternatives for sustainable soil fertility. Field experiments demonstrated the effectiveness of manure and compost application combined with mineral fertilizer on crop yields. Economic analysis indicated positive returns on investment for integrated nutrient management practices. These findings underscore the importance of farmer participation and integrated approaches to address soil fertility and promote sustainable crop-livestock integration in the Sahel.
The Native Shrubs Philiostigma reticulatum and Guiera senegalensis: The Unrecognized Potential to Remediate Degraded Soils and Optimize Productivity of Sahelian Agroecosystems
(2012-01) Richard P. Dick; Modou Sène ; Mateugue Diack; Mamadou Khouma; Aminata N. Badiane ; Samba Arona Ndiaye Samba; Ibrahima Diedhiou; Abel Lufafa; Ekwe L. Dossa; Fred Kizito; Sire Diedhiou; Jay Noller; Maria Dragila
The global objective of this study was to determine the unrecognized role of shrubs as key determinants in sequestration of C, water relations, and soil degradation mitigation in semiarid climatic regimes of Senegal that are representative of much of Sub-Sahelian Africa. The results showed that shrubs are the dominant controllers of hydrology, C biomass on the landscape, microbiology, and crop productivity in agroecosystem of Senegal. The major findings were: Shrubs residues decompose rapidly enough to allow non-thermal management. Shrub residues promote crop growth but it takes 2 years of incorporation before beneficial impacts on crops were measured. Both shrubs are doing hydraulic lifting of water from wet subsoils to dry surface soils Shrubs are non-competitive with crops for water and increase water and nutrient efficiency. During periods of excess rainfall shrubs promote groundwater recharge and therefore reduce surface runoff losses. G. senegalensis had the most profound impact on yields which after fours cropping the declining yields in the absence of crops resulted in a 242% difference in yield between plots with and with out this shrub. These positive impacts occurred even in the absence of fertilizer applications

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