|
||
|
|
|
|
||
 |
 |
Nutrient use efficiency in rice cropping systems: Special issue of Field Crops Research, 56(1-2):1-236, March 1998.
© 1998 Elsevier
Science
B.V. Reprinted with permission
NUTRIENT USE EFFICIENCY IN RICE CROPPING SYSTEMS Systems, Special Issue of Field Crops Research, 56(1-2):1-236 Note: Reproduction of this material excludes use in any electronic form other than on the IRRI Web site. Toward increasing nutrient-use efficiency in rice cropping systems: the next generation of technology K.S. Fischer International Rice Research Institute Rice production must increase by about 65% more than today to meet the demand projected for 2025. If the technologies that affect nutrient utilization by the rice crop remain unchanged, that production increase will require almost 300% more than the present application rate of N alone in irrigated environments. This is an undesirable amount economically and environmentally. The nutrient-use efficiency of rice cropping systems must be improved, along with yield potential of rice cultivars, in order to improve profitability of rice production and prevent environmental degradation in irrigated areas. Part of the projected demand for rice will be met through production increases in rainfed environments, where yields need to double from their present average of 2.0 t ha-1. The productivity of these systems is governed by interactions between water availability and the nutritional status of the crop. Cultivar improvement for tolerance to abiotic stress must be combined with management approaches that improve nutrient-use efficiency in such rainfed environments. (c) 1998 Elsevier Science B.V. Reprinted with permission. K.G. Cassman,1 S. Peng, D.C. Olk, J.K. Ladha, W. Reichardt, A. Dobermann, and U. Singh 1Agronomy Department, 279 Plant Science Building, University of Nebraska, Lincoln, Nebraska 68583-0915, USA; the coauthors are at the International Rice Research Institute Research and extension work to improve nitrogen (N) management of irrigated rice has received considerable investment because yield levels presently achieved by Asian farmers depend on large amounts of N fertilizer. Most work has focused on placement, form, and timing of applied N to reduce losses from volatilization and denitrification. In contrast, less emphasis has been given to development of methods to adjust N rates in relation to the amount of N supplied by indigenous soil resources. As a result, N fertilizer recommendations are typically made for districts or regions with the implicit assumption that soil N supply is relatively uniform within these domains. Recent studies, however, document tremendous variation in soil N supply among lowland rice fields with similar soil types or in the same field over time. Despite these differences, rice farmers do not adjust applied N rates to account for the wide range in soil N supply, and the resulting imbalance contributes to low N-use efficiency. A model for calculating N-use efficiency is proposed that explicitly accounts for contributions from both indigenous and applied N to plant uptake and yield. We argue that increased N-use efficiency will depend on field-specific N management tactics that are responsive to soil N supply and plant N status. Nitrogen-fertilizer losses are thus considered a symptom of incongruence between N supply and crop demand rather than a driving force of N efficiency. Recent knowledge of process controls on N cycling, microbial populations, and soil organic matter formation and decomposition in flooded soils are discussed in relation to N-use efficiency. We conclude that the intrinsic capacity of wetland rice systems to conserve N and the rapid N uptake potential of the rice plant provide opportunities for significant increases in N efficiency by improved management and monitoring of indigenous N resources, straw residues, plant N status, and N fertilizer. (c) 1998 Elsevier Science B.V. Reprinted with permission. Opportunities for increased nitrogen-use efficiency from improved lowland rice germplasm J.K. Ladha, G.J.D. Kirk, J. Bennett, S. Peng, C. K. Reddy, P.M. Reddy, and U. Singh International Rice Research Institute Understanding of the mechanisms governing the efficient use of N by rice plants - both its acquisition and internal use - is reviewed. Acquisition efficiency is considered in terms of root properties influencing the absorption and assimilation of NH4+ and other N species, and their regulation; root-induced changes in the rhizosphere affecting N mineralization, transformation and transport; and root-associated biological N2 fixation. Efficiency of internal use is considered in terms of the translocation, distribution and remobilization of absorbed N in different plant organs; flag leaf N import/export and leaf senescence patterns; and the efficiency with which N is used in CO2 fixation. Evidence for genetic variation in both acquisition efficiency and internal-use efficiency is given for plants under N-sufficient and N-limited conditions. The possibility of incorporating in rice the machinery for N2 fixation is discussed. (c) 1998 Elsevier Science B.V. Reprinted with permission. G.J.D. Kirk, T. George, B. Courtois, and D. Senadhira International Rice Research Institute The use of improved germplasm and management to increase rice production in rainfed lowland and upland systems is discussed. Understanding of the mechanisms conferring P efficiency, particularly external efficiency through root-induced changes in the rhizosphere, is reviewed together with evidence for genetic variation in P efficiency in upland and lowland rice germplasm. The following areas for improving resource and input management are considered: P management under alternately wet and dry soil conditions; P fertilizer formulations for banding in highly-weathered soils; cumulative responses to P fertilizer, including interactions with biological N fixation by legumes; amelioration of subsoil acidity, especially by leaching down the effects of surface-applied lime; and the management of soil spatial variability. Areas for future research are given. (c) 1998 Elsevier Science B.V. Reprinted with permission. Opportunities to manipulate nutrient-by-water interactions in rainfed lowland rice systems L.J. Wade, T. George, J.K. Ladha, U. Singh, S.I. Bhuiyan, and S. Pandey International Rice Research Institute Water stress, accompanied by changes in soil aeration, severely limits rice productivity in rainfed systems. These factors affect nutrient availability. Nitrate (NO3) that accumulates in aerobic soil is rapidly lost through leaching or denitrification in flooded soil. Green manures can act as NO3 catch crops and legumes may gain additional N from biological N fixation. Direct seeding permits additional crops to be grown. Roots are commonly shallow in rainfed lowlands. It is not clear to what extent rice yields in rainfed lowlands are limited by water, nutrients, and the interactions between them, over diverse soil types, cultural practices, and seasonal conditions. Research must determine what really limits root growth, water extraction and nutrient uptake. Some evidence suggests that manipulation of controlled-release fertilizer and root system development may be the key to optimizing nutrient release and capture in fluctuating environments. The potential for using strategic application of nutrients to buffer water limitation and stabilize yields must be examined. Models such as QUEFTS (Quantitative Evaluation of the Fertility of Tropical Soils) provide a potential framework for analyzing the effects of soil fertility and water availability on growth and yield of rice. (c) 1998 Elsevier Science B.V. Reprinted with permission. Management of phosphorus, potassium, and sulfur in intensive, irrigated lowland rice A. Dobermann1, K.G. Cassman2, C.P. Mamaril1, and J.E. Sheehy1 1 International Rice Research Institute 2 Department of Agronomy, University of Nebraska-Lincoln, P.O. Box 830915, Lincoln, Nebraska 68583-0915, USA Management of soil phosphorus (P), potassium (K), and sulfur (S) resources in intensive, irrigated rice systems has received less attention than increasing cropping intensity and yields with new cultivars, irrigation, and fertilizer N. Crop requirements, input-output balance, and soil supplying capacity of P, K and S in irrigated lowland rice are reviewed. Based on projected rice production requirements, we estimate that the total annual nutrient demand for irrigated rice will be about 9 to 13 x 106 t N, 9 to 15 x 106 t K, 1.2 to 2.4 x 106 t P and 0.9 to 1.5 x 106 t S in 2025, amounts that represent an increase of 65 to 70% above 1990 requirements. At present, negative K balances are widespread and K deficiency has become a constraint to increasing yields, even on heavy-textured lowland soils with high inherent fertility. Because opportunities are limited for breeding cultivars that acquire more P, K, or S from soil or have higher internal nutrient-use efficiencies, long-term management strategies must focus on maintaining adequate nutrient balances in the topsoil layer. Interactions among nutrients have a large influence on physiological and agronomic efficiency that result from nutrient applications. Strategies that only aim at increasing P or K application rates without considering the indigenous supply from soil reserves are inefficient; they may not sustain yield increases to meet rice demand. Little improvement in fertilizer use efficiency can be expected from the present system of providing blanket recommendations for a given production domain. Instead, site-specific nutrient-management approaches will be needed to accommodate the tremendous variability in indigenous nutrient supply found in the irrigated lowlands of Asia. (c) 1998 Elsevier Science B.V. Reprinted with permission. Strategies for dealing with micronutrient disorders and salinity in lowland rice systems H.U. Neue1, C. Quijano2, D. Senadhira2, and T. Setter2 1 UFZ-Center for Environmental Research, Department of Soil Sciences, Hallesch Strasse 44, Bad Lauchstaedt, Germany 2 International Rice Research Institute In wetland rice, the most commonly observed micronutrient disorders are Zn deficiency and Fe toxicity. Salinity is the main obstacle to high yields in coastal areas in the humid tropics and in arid and semiarid areas where evaporation exceeds precipitation. To develop sustainable rice production systems in areas where these stresses occur, cultivar tolerance is often essential, though improved management also plays an important role. In the last 15 years, IRRI research has focused on germplasm improvement. Intensive screening and breeding have resulted in high tolerance to Zn deficiency in IRRI's late elite lines; screening methods are available, but tolerance mechanisms and genetics are not yet fully understood. Recent work has shown the importance of root-induced changes in the rhizosphere for solubilizing Zn and increasing its plant uptake. Repeatable screening methods are not yet available for isolating genotypes with tolerance to Fe toxicity. Pot and field methods earlier developed do not allow screening of sufficient numbers of rice lines for an effective breeding program. A greenhouse screening procedure using a 400 mg L-1 iron solution is being tested. Genetic studies are required but may only be feasible when additional knowledge of mechanisms is available. Pre-breeding efforts for salinity have resulted in adequate knowledge on mechanisms, genetics and reliable screening techniques. Salt-tolerant rice cultivars with targeted agronomic characteristics and yield potentials are now available. (c) 1998 Elsevier Science B.V. Reprinted with permission. Economics of nutrient management in Asian rice systems: Towards increasing knowledge intensity P.L. Pingali1, M. Hossain2, S. Pandey2, and L. Leimar Price2 1 International Maize and Wheat Improvement Center (CIMMYT) Apdo Postal 6-641, 06600, Mexico D.F., Mexico 2 International Rice Research Institute Although increase in rice production during the Green Revolution era of the past three decades was based on increased irrigation and fertilizer use, technologies and policies to enhance fertilizer-use efficiency will be needed in most of the intensive rice production areas in the coming decades. In less intensive areas, opportunities exist for further increasing fertilizer use by reducing risk through cultivar improvement and better management. As opposed to simple "blanket" recommendations, improved efficiency requires conditional "if-then" types of rules. Such recommendations, to be acceptable to farmers, should not only be cost-efficient but also must fit into the farmers' knowledge systems and provide them with enough flexibility for experimentation and learning. In addition to technologies, policy reforms such as the removal of fertilizer subsidies are needed to make nutrient-efficient practices economically profitable to farmers. (c) 1998 Elsevier Science B.V. Reprinted with permission. Sulfur and carbon research in rice production systems G. Blair and R. Lefroy Department of Agronomy and Soil Science, University of New England, Armidale, NSW, 2351 Australia Sulfur is a critical nutrient for crop growth, but quantifications of inputs of S into rice production systems are lacking. Recent research has allowed the development of methods to quantify S inputs from rainfall, crop residues, and from the soil pool. The efficiency of S fertilizer use depends on the S source, and its placement and time of application. The S cycle is complex, and depends strongly on the availability of C, which serves as an energy source for microorganisms. Evidence of movement of labile C down the soil profile has implications for both N and S nutrition. (c) 1998 Elsevier Science B.V. Reprinted with permission. Genetic responses of oat genotypes to environmental factors K. Frey Department of Agronomy, Iowa State University, Ames, IA 50011-1010, USA Results are summarized for a number of cultivar evaluations and selection studies for oat (Avena sativa L.). Modern cultivars were found to be more tolerant of drought stress than older cultivars, and this tolerance has led to greater yield stability in stress environments. In a separate study, we observed large cultivar differences for heat tolerance. The importance of genetic differences in abiotic stress tolerance is supported by the results of empirical selection studies. The relationship between grain yield and grain protein content was negative in crosses between some oat lines, while in other crosses there was no relationship between the traits. These relationships persisted over several cycles of selection. Other selection studies revealed that greater yield gains were achieved in low yield environments when selection was performed under stress. These results have implications for cultivar improvement strategies for nutrient-poor environments. (c) 1998 Elsevier Science B.V. Reprinted with permission. K.R. Helyar Agricultural Research Institute, NSW Agriculture, PMB, Wagga Wagga, NSW, 2650, Australia Investment in fertilizer must be profitable for soil fertility to be sustainable for commercial agriculture, otherwise only an exploitative system can be operated. Three methods of increasing the marginal return from fertilizer application to the marginal cost ratio to above one are considered: increasing the product price and/or decreasing the fertilizer cost; improving the efficiency of nutrient utilization through improved extension; and improving the efficiency of nutrient utilization by developing new cultivars and management techniques. Phosphorus (P) is used as an example and most emphasis is placed on the third method. Maximizing the efficiency of P utilization is equated with minimizing the P fertilizer rate required to maintain the economically optimum P fertility status of a system. Ultimate efficiency is achieved in a system where the maintenance P fertilizer rate is equal to P removal in product. Losses of P in run-off, eroded material and leachate are usually minimal in well-managed systems so the main means of increasing efficiency are to minimize the accumulation of P in the soil as organic and inorganic P. Accumulation of inorganic soil P is minimized by maximizing plant demand and minimizing soil reactions (removing yield limitations due to factors other than P deficiency, placing P fertilizer in zones with active root growth, avoid fertilizing in excess of plant requirements). Establishing crop rotations that maintain soil organic matter will limit loss of applied P into the organic pool. Opportunities for increased efficiency of P utilization through cultivar improvement include selection for traits that favor strong plant demand such as late maturity, increased longevity of rootlet activity, and increased P solubilization capacity. It is suggested increased root surface area per unit of P required may be a useful index to indicate cultural conditions and varietal characteristics that favor strong plant demand on soil P and thus minimize soil losses. (c) 1998 Elsevier Science B.V. Reprinted with permission. Efficient use of nutrients: An art of balancing| B.H. Janssen Department of Soil Science and Plant Nutrition, Wageningen Agricultural University, P.O. Box 8005, 6700 EC, Wageningen, The Netherlands Nutrient-use efficiency is conceived as the product of uptake efficiency, i.e. the ratio of actual uptake to potential supply, and utilization efficiency, i.e., the ratio of yield to actual uptake. Both depend on the availability of the nutrient in relation to other growth factors, and require N, P and K perfectly in balance to reach their maximum values. Hence, the cause of a low recovery of fertilizer nutrients may be wastage due to unbalanced supplies of nutrients, apart from fixation in the soil or loss from the soil. The ratios of the supplies of N, P, and K for nutritional balance were established and used for the calculation of "nutrient supply equivalent", defined as the supply of a nutrient that has the same effect on yield as a supply of 1 kg N. A triangular diagram is proposed with supply equivalents of N, P, and K along the sides. At each point in the diagram, the sum of supply equivalents is 100%, and maximum nutrient efficiency is found in the centre. In the field, the influence of other growth factors on nutrient-use efficiency usually consisted of a direct effect on nutrient utilization efficiency, and an indirect effect on nutrient uptake efficiency. The latter was partly driven by utilization efficiency. Sunny weather and soil biological activity acted positively in this way, and soil acidification and moisture stress negatively. (c) 1998 Elsevier Science B.V. Reprinted with permission. H. Marschener Institute of Plant Nutrition, University of. Hohenheim, Stuttgart, Germany Genotypic differences in nutrient acquisition are important determinants of nutrient-use efficiency. These differences can be related to root size and morphology and/or to root physiology. Root surface area can be enhanced through mycorrhizal associations. Root processes can affect rhizosphere pH and redox potential. In addition, root exudates affect rhizosphere chemistry. Exudation may be responsive to a particular nutrient deficiency. For example, P deficiency can induce the release of organic acids and/or acid phosphatases, and iron or Zn deficiencies result in the release of phytosiderophores by some species. Thus, in light of the diverse plant responses to nutrient-deficient soils, it will be necessary to identify the key mechanism(s) of tolerance in a particular field environment before initiating mass screening for a specific tolerance mechanism. (c) 1998 Elsevier Science B.V. Reprinted with permission. Nitrogen utilization efficiency in maize and grain sorghum R.C. Muchow CSIRO Division of Tropical Crops and Pastures, 306 Carmody Road, St Lucia, Q. 4067 Australia The efficiency of utilization of N by maize and sorghum (defined as grain yield per unit N uptake) varies under different climatic, soil, and management conditions. To maximize N-use efficiency, the minimum N requirement for a given yield level must be established. The maximum N-use efficiency (NUE) of sorghum was smaller than for maize (48 vs. 61 g grain-1 g-1 N absorbed), and was associated with a higher grain N concentration in sorghum. Cultivar differences in NUE in sorghum were related to grain N concentration. In both crops, NUE declined when N was supplied at high levels or when growth was limited by moisture supply. These conditions result in increased stem and grain N concentration. Crop models can integrate the effects of abiotic factors on grain yield, and allow the development of strategies for improving the utilization of N to maximize grain yield and to minimize N losses from the production system. (c) 1998 Elsevier Science B.V. Reprinted with permission. Modifying rhizosphere microbial communities to enhance nutrient availability in cropping systems D.A. Phillips and W.R. Streit Department of Agronomy and Range Science, University of California, Davis, CA 95616 USA Microorganisms can contribute significantly to improving nutrient-use efficiency in cropping systems. Traditional approaches to increasing the number of beneficial microorganisms have been hampered by competition with indigenous populations. New opportunities exist as a result of advances in molecular genetics. Compounds produced by the plant can regulate bacterial genes, and this information can be used to induce natural and/or foreign genes supplied to soil bacteria. New techniques make it possible to maintain introduced plasmids in soil bacteria, and inserting into those plasmids particular genes that enhance mineral availability, disease resistance, or pesticide degradation will be an important tool for managing future cropping systems. (c) 1998 Elsevier Science B.V. Reprinted with permission. Research opportunities to improve nutrient-use efficiency in rice cropping systems H.R. Lafitte International Rice Research Institute This is a summary of discussions and conclusions from a workshop on nutrient-use efficiency of rice cropping systems, held 13 -15 December 1995 at the International Rice Research Institute, Los Baños, Philippines (Field Crops Research, Special Issue, Vol.56, No. 1-2, March 1998). Workshop participants reviewed current research in crop management and genetic improvement of rice, and concluded that increased rice production will depend on explicit considerations of nutrient supply. For intensive irrigated rice systems, research priorities include understanding how soil nutrient supply is linked to cropping intensity, what pattern of nutrient supply is required to achieve the high yield levels needed to meet the needs of rice consumers in the next century, and how to improve congruence of nutrient supply and crop demand through management. In rainfed environments, nutrient demand is closely linked to water availability, and participants saw a need to characterize environments according to the different patterns of resource limitations. Soil and climate databases will be important in this effort. An explicit conceptual framework must underlie field work in these variable environments, and simple simulation models were identified as essential tools for targeting experiments and pre-testing improved technologies. Cultivar improvement for efficient nutrient use can complement agronomic approaches. The potential gains in improved nutrient acquisition and/or improved physiological efficiency are not clear for all nutrients, and these need to be estimated in order to set breeding priorities. Improved screening techniques related to specific mechanisms of nutrient efficiency will facilitate genetic improvement. Promising research approaches are described to address each of these constraints to improving nutrient-use efficiency in rice. (c) 1998 Elsevier Science B.V. Reprinted with permission. |
|
|
|
Opportunities for increased nitrogen-use efficiency from improved lowland germplasm Opportunities to manipulate nutrient-by-water interactions in rainfed rice systems Management of phosphorus, potassium, and sulfur in intensive, irrigated lowland rice Strategies for dealing with micronutrient disorders and salinity in lowland rice systems Economics of nutrient management in Asian rice systems: toward increasing knowledge intensity Sulfur and carbon research in rice production systems Genetic responses of oat genotypes to environmental factors Efficient use of nutrients: an art of balancing Role of growth, arbuscular mycorrhiza, and root exudates for the efficiency in nutrient acquisition Nitrogen utilization efficiency in maize and grain sorghum Modifying rhizosphere microbial communities to enhance nutrient availability in cropping systems Research opportunities to improve nutrient-use efficiency in rice cropping systems |
|
|
|
