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Rainfed lowland rice: Advances in nutrient management researchRAINFED LOWLAND RICE: ADVANCES IN NUTRIENT MANAGEMENT RESEARCH Proceedings of a workshop, 12-15 Oct. 1998, Ubon, Thailand Edited by J.K. Ladha, L.J. Wade, A. Dobermann, W. Reichardt, G.J.D. Kirk, and C. Piggin Nutrient management technologies for rainfed rice in tomorrow's Asia: economic and institutional considerations S. Pandey Although the area of intensive irrigated rice is the main food basket of Asia, the crop's higher productivity in rainfed lowlands holds the key to improved food security in the coming decades. The average yield of rainfed rice is low, but the potential to increase its productivity through improved technology, including improved nutrient management, exists. A targeted approach to nutrient management research is suggested because of differences in the nature of the rainfed rice system across regions. The nature of nutrient management technology requires changes as the economic forces that affect agriculture change during the process of economic growth. In areas with a low use of nutrients, rice varieties and crop management technologies that reduce risk are needed to encourage the increased use of fertilizers. Where fertilizer use is already high, cost-effective technologies that improve nutrient-use efficiency are needed. Policy interventions such as the removal of price subsidies for fertilizers, investments in infrastructure, a greater emphasis on the decentralization of adaptive research, and reorientation of extension systems to deliver information rather than technical packages are critical to the success of these technologies. Nutrient research on rainfed lowland rice in relation to the 1995 review L.J. Wade In October 1998, an International Workshop on Nutrient Research in Rainfed Lowlands was held at Ubon Ratchathani, Thailand, as a thematic review for the Rainfed Lowland Rice Research Consortium. The 18 papers presented appear in this volume, together with recommendations from two working groups, which addressed understanding of nutrient dynamics and development of nutrient management strategies and technologies. This paper provides the background to the workshop by briefly describing the characteristics of rainfed lowland rice systems and summarizing the state of knowledge on nutrients in those systems as of 1995, when nutrient-use efficiency in rice cropping systems was last reviewed at the International Rice Research Institute. Recommendations from the 1995 external review are presented, before outlining where these recommendations are addressed in subsequent research. Other papers in this volume provide further details on research progress. P. White, T. Oberthür, A. Dobermann, and R. Chhay Simple soil classifications that enable nonexpert soil scientists to identify soils in the field are important for applying technologies to individual soil situations. This paper describes a soil classification system developed for agronomists in Cambodia that has proved useful in improving soil fertility management. This classification system relies on soil characteristics that are easily identifiable in the field and have agronomic relevance. The system was used in the on-farm trial program of the Cambodia-IRRI-Australia Project in 1996 and 1997 to determine whether it could adequately discriminate between soil types and improve fertility management. Analysis of soil samples collected throughout the rice-growing areas showed that 40-55% of the overall variation in sand, clay, organic C, CEC, and extractable Ca, Mg, and K could be accounted for by soil groups described in the soil classification system. Soil-specific fertilizer recommendations enabled by the classification system also adequately predicted differences in grain yields of rice grown on the different soils. The Fertility Capability Classification of Sanchez and Buol (1985), incorporated into the system, provides wider applicability for classifying and facilitating the transfer of agronomically important soil information between the rice-growing areas of Cambodia and northeast Thailand. Local agronomists have welcomed the system. Evaluating nutrient deficiencies and management strategies for lowland rice in Lao PDR B. Linquist, P. Sengxua, A. Whitbread, J. Schiller, and P. Lathvilayvong Rice is the single most important crop in Lao PDR and is grown on 88% of the cultivated area. More than 80% of the rainfed lowland rice area is in the central (CR) and southern (SR) regions of Lao PDR, where most rice is grown on six plains adjacent to the Mekong River. Soils are predominantly coarse-textured with low pH and organic matter levels. Average rice yields without fertilizer are 2 t ha-1. In the northern mountainous region (NR), lowland rice soils are primarily loams with higher native soil fertility (yields average 2.6 t ha-1 without fertilizer). Nitrogen and phosphorus are the primary limiting nutrients in all regions, although the response to both N and P is greater in the SR and CR than in the NR. Most nutrient research has focused on N and P management. The objective of N management research has been to improve N-use efficiency through improved timing of N applications, selection for N-responsive varieties, and green manure use. Most research on P has focused on determining adequate P application rates to alleviate P deficiencies and improve P management in green manure-rice systems. Potassium and sulfur deficiencies are less common, although we anticipate that the increased use of N and P fertilizers will result in a greater incidence of these and other nutrient deficiencies. In this paper, we discuss soils, potential nutrient problems, and nutrient management strategies, and suggest priorities for future nutrient management research in Lao PDR. R.D.B. Lefroy and Y. Konboon We need to develop improved management systems for marginal uplands and rainfed lowlands to meet the challenges facing world agriculture. Although fertilizers have played an important role in increasing agricultural production on productive lands over the past 40 years, nutrient management is critical for increasing productivity and achieving sustainability on more marginal lands. We have used nutrient budgets to indicate major imbalances in agricultural systems, although accurate nutrient budgets are complex. We lack both data and a sufficient understanding of some of the underlying processes in developing nutrient budgets; both need to be improved. Simple nutrient balances were calculated for rice production in Thailand, the Northeast region, and Ubon Ratchathani Province. These generally indicated positive balances for N and P and some negative balances for K. But significant problems result in these calculations from inadequate data and from ignoring certain important loss processes. R.K. Shrestha and J.K. Ladha Increases in the yield of rainfed land tend to occur more slowly than population growth mainly because of complex and variable environmental factors and the more limited knowledge base of research. The nature of alternate wet and dry conditions of rainfed lowlands with increasing cropping intensity and the use of chemical inputs pose a challenge to sustainability in lowlands. The recent shift in research priorities to rainfed lowlands, which they deserve, has identified important nutrient issues related to management, especially for the most volatile nutrient, nitrogen. The input-intensive rainfed tropical ecosystem, where wet-season rice-dry-season diversified high-value upland crops predominate, has resulted in a problem of a large leakage of N into the environment, thereby polluting the air and water. Losses of up to 550 kg N ha-1 have been reported from certain rice-vegetable systems. Much of this N found its way into groundwater, resulting in NO3- concentrations that exceed the limit set for drinking water. Integrated management strategies such as matching nutrient supply and demand, capturing residual nutrients by integrating catch crops in the dry-to-wet transition, and recycling residue for succeeding crops offer opportunities to maintain soil fertility and improve plant nutrition. S.K. Patil, R.O. Das, V.N. Mishra, V.P. Singh, and U. Singh Effective management of native soil nutrients could have a significant effect on increasing and stabilizing rice yield in rainfed lowlands. Nitrogen can be recycled in monoculture rice by including a legume as a postrice crop on residual moisture and winter rains. The N accumulated may be lost early during the wet season if it is not managed properly. Because fertilizer application rates are very low, the rice crop relies mostly on native nutrients. Such losses of mineral nutrients are obviously not desirable for rainfed lowlands. It is important to develop strategies that help to make the most effective use of native and applied nutrients. Rice crop establishment methods and legume inclusion in the system may provide options for making a more effective use of soil N and P. This paper highlights strategies for making the best use of residual soil N and P in rainfed lowland cropping systems. We discuss research results generated from the use of these strategies and future research needs. Potassium balances in rainfed lowland rice on a light-textured soil A. Wihardjaka, G.J.D. Kirk, S. Abdulrachman, and C.P. Mamaril An experiment was carried out over 3 years to compare the effects of mineral fertilizers and organic manures on potassium (K) balances in rainfed lowland rice on a light-textured Tropaqualf. Two rice crops were grown per annum: the first was direct-seeded (DS) in moist soil that was later flooded; the second was transplanted (TP) into flooded soil. A soybean crop followed the TP rice in the first year. Potassium balances were generally negative. For DS rice, the relations between grain yield and K uptake fell within the limits of maximum K dilution and maximum K accumulation expected for well-managed irrigated rice. But those for TP rice tended to fall below the limit of maximum accumulation, yield being constrained by factors other than mineral nutrition. In the DS rice, grain yields per unit K uptake were close to maximum in the treatments that received no K, but they were well below maximum in the K-fertilized treatments. Uptake was well correlated with ammonium acetate-extractable K in the soil at maximum tillering. But the mass balances of K inputs, K uptake, and extractable K in the soil showed that a large part of the uptake was from nonextractable pools. The mobilization of nonextractable K was apparently plant-induced and was greater in treatments with better growth. A mechanism for root-induced solubilization of nonextractable K is proposed. W. Reichardt, S. Meepetch, A.M. Briones, S. Ruaysoongnern, and K. Naklang Substantial and economically sound improvement of the fertility of heavily weathered acid sandy rice soils in northeastern Thailand requires a better insight into mechanisms that govern the sustainable supply of soil nutrients. The extreme type of drought-prone rainfed lowland rice soil in this region presents a particular challenge to current concepts on the key role of microbial biomass and biocatalytic microbe-mediated soil nutrient supply. Enhancing the extremely low biomass level and improving the unsatisfactory status of the inherent microbial communities in these soils has emerged as a promising management option. Yet to what extent the unique composition of the acid sandy soil biomass with its prokaryotic and eukaryotic segments can be maintained will have to be studied. Increasing the soil buffering capacity and cation exchange capacity through a microbe-driven buildup of a sustainable organic matter phase can be a major target of future fertility improvement research. Further, and not less promising, management options could exploit root-associated microorganisms that have the potential to store nutrients or to otherwise enhance or secure the supply of nutrients to the plant. Using organic material to improve soil productivity in rainfed lowland rice in Northeast Thailand N. Supapoj, K. Naklang, and Y. Konboon The Ubon Ratchathani Rice Research Center is conducting a number of field experiments in the southern part of Northeast Thailand to assess whether the generally low rice yields and poor soil quality could be improved despite uncertain rainfall. The major objectives are (1) to determine the role of soil conditioners in improving soil fertility and rice yields, and (2) to evaluate different organic materials for manuring. This research program involves (1) using rice straw and residues from rice to improve soil, (2) integrating legume crops with rice, and (3) managing nutrients for dry-seeded rice cultivation. It was found that applying organic materials, such as plant residues, rice straw, and rice husks, significantly improved rice yields and soil productivity. The residual of these materials also had a large impact on the growth of rice. Legumes integrated with the rice crop were also found to increase rice yields. We concluded that these strategies or a combination of them could partly overcome the adverse climatic and soil environment as well as diminish inputs to ecologically and economically sustainable levels. Y. Konboon, K. Naklang, D. Suriya-arunroj, G. Blair, A. Whitbread, and R. Lefroy An in vitro perfusion technique has been used to determine the breakdown rate of wheat straw and four legumes (Flemingia macrophylla, Albizia chinensis, Medicago truncatula, and Cicer arietinum). Although the four legumes had similar C:N ratios, their rate of breakdown varied markedly and could be related to a plant residue quality index, which includes C:N ratio and lignin and tannin concentration. The effect of incorporation into soil of the same five materials on the yield of two successive wheat crops was examined in a glasshouse pot experiment. Adding C. arietinum, which has a rapid breakdown rate, resulted in the highest wheat yield in the first crop. Yield was highest in the A. chinensis (slow breakdown rate) treatment in the second crop. Marked differences were recorded between species in the apparent recovery by the wheat crops of the nutrients they contained. A field trial at Ubon, Thailand, has shown that flooded-rice yields increased the most with the annual application of low rates (1,500 kg dry matter ha-1) of leaf litter from Cajanus cajan, Phyllanthus taxodifolius, Acacia auriculiformis, and Samanae saman. The four seasons of leaf litter application increased the total (CT) and labile (CL) carbon pool by 11-21% and 7-27% relative to a no-residue control, respectively. A carbon management index (CMI), which incorporates changes in labile and nonlabile C pools, was found to be able to detect changes in soil C over the 6-yr trial. Indigo: a farmer-proven green manure E.O. Agustin, S.R. Pascua Jr., J.K. Ladha, T.F. Marcos, and S.R. Obien Indigo (Indigofera tinctoria L.) was introduced in the Philippines as a source of dye but has been adopted as a green manure by farmers in the northwestern provinces of Luzon. Farmers in these provinces integrate indigo as an intercrop of the dry-season components of various rice-based cropping systems in the rainfed lowland ecosystem. They use indigo to replace and supplement chemical fertilizers and to improve soil fertility. Both farmers' experiences and research results show higher rice grain yields in fields previously planted and incorporated with indigo than in those without indigo. Research results also show that indigo has other effects apart from supplying N to crops. E.G. Castillo, T.P. Tuong, R.C. Cabangon, A. Boling, and U. Singh The effects of crop establishment and controlled-release fertilizers on drought stress responses of rice (Oryza sativa L.) cultivar PSBRc 14 were evaluated in a field experiment with a split-split-plot design. The main plots were two water treatments (continuously flooded and drought-stressed at panicle initiation). In the three subplots, rice was established by dry seeding (DS), transplanting (TP), and wet seeding (WS). In the sub-subplots, prilled urea was compared with two controlled-release N fertilizers (Polyon 12 wk and POCU-S 120 d) at a rate of 80 kg ha-1. Prilled urea was applied in four splits to minimize the drought-induced N-fertilizer loss. The controlled-release fertilizers (CRF) were applied at crop establishment. Drought prolonged crop maturity by 10-14 d. Drought stress hindered grain formation, resulted in sink limitation, and increased straw biomass during the stress-recovery stage. Drought treatments significantly reduced grain yield, but not the total biomass and total N uptake. Under flooded conditions, yields in all fertilizer treatments were comparable. In the stress treatments, Polyon 12 wk produced the lowest yield. Dry-seeded rice had a lower yield in the control treatment, but a higher yield in the stress treatment compared with TP and WS rice. The higher yield of DS rice under stress conditions could be related to its significantly higher root length density and higher root-zone available soil moisture during the stress period. CRFs may help alleviate the need for a split application of fertilizer in drought-prone conditions, but it is important to take into account the drought-induced prolongation of crop duration in selecting the CRF release time. Nutrient management in rainfed lowland rice for the High Barind Tract of Bangladesh M.A. Mazid, L.J. Wade, M.A. Saleque, A.B.S. Sarker, M.I.U. Mollah, A.B. Olea, S.T. Amarante, and C.G. McLaren Field experiments were conducted in the High Barind Tract of Bangladesh at high, medium, and low toposequences for 2 years to evaluate the efficiency of different fertilizers for rainfed lowland rice and to explore the possibilities of cultivating chickpea after rice in this single-cropped rice area. At each site, nine fertilizer treatments-nil, PK, NPK, NPKS, controlled-release N + PKS (CR-NPKS), farmyard manure (FYM), 50% FYM + 50% NPK (1/2 FYM + 1/2 NPK), neem cake, and biogas slurry-were tested in a randomized complete block design with three replicates. Chickpea was grown after rice without fertilizer. The study was conducted for 2 years in the same layout. In all the toposequences, applications of PK alone showed no response compared with the no-fertilizer (control) application. Two-year results showed that the application of nitrogen (N) fertilizers significantly increased rice yield over the control. Nitrogen was found to be the most limiting macroelement in the system. The highest grain yield of rice was obtained in the plots that received CR-NPKS, NPKS, and NPK, followed by the combined application of 1/2 FYM + 1/2 NPK, and neem cake. Among the organic sources, neem cake had a better performance in terms of grain yield and N efficiency than did FYM and biogas slurry. Because of its medium duration (125-130 d), modern rice variety BR32 escaped the water stress that commonly occurred in October. Moreover, it was possible to grow chickpea after rice using the residual soil moisture. Organic sources such as FYM, biogas slurry, and the combination of 1/2 FYM + 1/2 NPK provided some residual benefit to the chickpea, as did PK alone. Chickpea grain yield varied from 1.60 to 2.03 t ha-1, increasing the overall productivity and gross returns in this drought-prone rainfed lowland rice environment. B.K. Samson and L.J. Wade Rainfed lowland rice accounts for approximately 33% of the total area grown to rice worldwide; hence, it encompasses a diverse range of environments and soils. The common themes of total dependence on rainfall and, consequently, the absence of water control, and of traditionally transplanting rice seedlings on puddled soil run through these diverse settings. A recent trend toward direct seeding of rice is driven by the scarcity of labor and is made possible by the availability of earlier maturing varieties. Such divergence in crop establishment practices gives rise to issues related to how much water the rice crop and postrice crop are able to use. Different approaches to dealing with the need to conserve rainwater and to use subsoil water and nutrient resources become apparent for coarse- and fine-textured soils. We discuss soil physical constraints within this environmental context as they relate to the ability of rice roots to grow and to extract water and nutrients from the soil. We present current data on growth of roots and indications of their functional ability. We identify research issues and questions at the end of the paper. G. Trébuil, D. Harnpichitvitaya, T.P. Tuong, G. Pantuwan, L.J. Wade, and S. Wonprasaid Two-factor field experiments during 1993 and 1994 with sharply contrasting wet seasons were carried out for in situ water conservation and nutrient use in rainfed lowland rice (Oryza sativa L.) grown on a sandy soil. The main plots compared subsoil compaction with shallow dry tillage (C1), subsoil compaction with deep dry tillage (C2), and shallow dry tillage without compaction (C0). Five mineral fertilization techniques were used as subplot treatments: no fertilizer (control, F0), 40-13-25 kg NPK ha-1 in two applications of conventional fertilizer (F1), 40-13-25 kg NPK ha-1 using slow-release fertilizer (F2), 80-26-50 kg NPK ha-1 in two applications of conventional fertilizer (F3), and 80-26-50 kg NPK ha-1 using slow-release fertilizer (F4). Soil was compacted with 10 passes of a vibrating road roller on 15 May 1993. Rice seedlings (cv. RD6) were transplanted in all plots. Compaction increased total weeks with surface water accumulation from 3.7 and 2.4 wk in C0 to 11.0 and 14.3 wk in C1, and 11.7 and 14.9 wk in C2 for the 1993 and 1994 wet seasons, respectively. Because three irrigations were applied during the 1993 WS, drought stress was far more severe during the nonirrigated 1994 WS. With the single exception of the effect on rice grain weight in the 1994 WS, no significant interaction between the main factors (compaction) and (fertilization) subfactors was observed. Although the highest grain production was also harvested in compacted plots in the 1993 WS, grain yield increase because of subsoil compaction was found to be significant (P<5%) in the 1994 WS only. Grain yield in C2 plots was 2.2 t ha-1 versus 1.8 t ha-1 in C1 plots and 0.8 t ha-1 in C0 plots. The difference in grain yield between C1 and C2 was also statistically significant. Effects of mineral fertilization were significant in the 1993 WS only. The F4 slow-release fertilizer-based treatment gave a grain yield of 3.2 t ha-1 compared with 1.4 t ha-1 in the F0 plots. Corresponding values for F1, F2, and F3 were 1.9, 2.3, and 2.3 t ha-1. Partly because of the severity of the drought stress, no significant yield differences between fertilizer treatments were measured in the 1994 WS. The combination of subsoil compaction and slow-release fertilizer techniques constitutes a way to increase soil productivity and stabilize RLR yields to improve food security and incomes at the farm level. Although these techniques could help mitigate climatic risk, they did not appear to improve soil water conditions for increasing cropping intensity. Further investigations are needed to assess their economic profitability and recommendation domains in such a heterogeneous and variable rice ecosystem that is mostly populated by resource-poor farmers. The importance of rhizosphere processes in the mineral nutrition of rainfed lowland rice V. Römheld Root growth characteristics and rhizosphere processes are decisively important for water and nutrient acquisition by plants. An understanding of these has been used to develop improved genotypes and management for upland crops and forest trees. But an equivalent understanding has yet to be developed for the rhizosphere of rice under submerged soil conditions, particularly under the fluctuating water regimes of rainfed lowland rice environments. This lack of understanding constrains the development of improved rainfed lowland rice genotypes and management practices. Genotypic variation at low soil fertility in drought-prone rainfed lowland environments S. Fukai Low soil fertility and drought reduce the grain yield of rainfed lowland rice in many Asian countries. This work documents cultivar requirements for low soil fertility conditions in drought-prone rainfed lowland environments, particularly in Thailand and Lao PDR. Genotypic variation in grain yield can be analyzed in relation to uptake and use of limiting nutrients. Experimental results are available mostly in irrigated conditions. These and limited information from research conducted recently in Australian Centre for International Agricultural Research (ACIAR) projects suggest that both nutrient uptake and nutrient-use efficiency to produce grain yield are important for the adaptation of particular cultivars to low soil fertility environments. Use efficiency can be improved by developing cultivars that require a low nutrient concentration in the plant and a higher allocation of nutrient to the grain. |
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Nutrient research on rainfed lowland rice in relation to the 1995 review Evaluating nutrient deficiencies and management strategies for lowland rice in Lao PDR Potassium balances in rainfed lowland rice on a light-textured soil Using organic material to improve soil productivity in rainfed lowland rice in Northeast Thailand Indigo: a farmer-proven green manure Nutrient management in rainfed lowland rice for the High Barind Tract of Banglasesh The importance of rhizosphere processes in the mineral nutrition of rainfed lowland rice Genotypic variation at low soil fertility in drought-prone rainfed lowland environments |
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