Accounting for environmental and socioeconomic sustainability in Northeast Thailand: towards decision support for farmers and extension workers

Sustainable agricultureFarming systemsFertilizersEconomic aspectsIncome

Sequestering soil carbon in the low input farming systems of the semi-arid tropics – does litter quality matter?

Maintaining soil organic matter (SOM) in low input smallholder rice cropping systems worldwide is of paramount importance to maintaining livelihoods and food security. A long term rainfed lowland rice experiment tested the hypothesis that applying small (1.5 t/ha dry matter) annual additions of slowly decomposable plant materials which were grown offsite and applied prior to land preparation, could result in increased soil organic carbon, crop yield and improve the recovery of nutrients compared with plant materials of higher quality or straw retention alone. Annual leaf litter applications over 9 seasons resulted in significant increases in SOC of 39% (from 3.5 to 4.9 mg/g) in the leaf litter treatments compared to only 13 % in the noleaf litter control. In terms of rice grain production and nutrient use efficiency, leaf litter quality was an important driver. Apparent nutrient recovery of nitrogen and sulfur reflected the decomposition rate of the added residues. Sustainable farming systems will require that crop yields are stable through the maintenance of soil fertility and the balanced use of nutrients in the system. The results of this study are therefore highly significant and provide evidence that low rate, long term residue management can have profound effects

Nutrient management for rainfed lowland rice in northeast Thailand

Abstract not availableS.M. Haefele, Y. Konboo

Black carbon (Biochar) in rice-based systems: characteristics and opportunities.

The total amount of crop residues produced each year in rice-based systems of Asia can be roughly estimated at about 560 million tons of rice straw and about 112 million tons of rice husks (based on 2005 production, a harvest index of 0.5, and a husk/paddy ratio of 0.2). These residues constitute a valuable resource, but actual residue management practices do not use their potential adequately and often cause negative environmental consequences. In the past decades, increasing opportunity costs of organic fertilizer use and shortened fallow periods due to cropping intensification caused a continuous decline in the recycling of crop residues (Pandey 1998). Residue burning is widely practiced and causes air pollution, human health problems, and considerable nutrient losses. The declining return of organic materials to soils does not seem to affect soil quality in mostly anaerobic systems (rice-rice) with good soils but residue recycling is important to maintain soil fertility on poor lowland soils, in mixed cropping systems (rice-upland crop), and in upland systems (Dawe et al. 2003; Ladha et al. 2003; Tirol-Padre and Ladha 2006). Global climate change raises further questions about rice residue management. Decomposition of organic matter in flooded rice is always related to emissions of methane, which is about 22 times more radiatively active than CO2, and rice-based systems are estimated to contribute 9% to 19% of global methane emissions (Denman et al. 2007). In addition, the rapidly increasing interest in renewable energy sources adds new options and consequences for rice residue management and rice-based systems. An opportunity to address these issues in a completely new way arises from research on anthropogenic soils in the Amazonian region called terra preta de índio (Sombroek 1966). These soils are characterized by high contents of black carbon (carbonized organic matter, biochar) most probably due to the application of charcoal by Amerindian populations 500 to 2,500 years ago. They are also distinguished by a surprisingly high and stable soil fertility contrasting distinctively with the low fertility of the adjacent acid and highly weathered soils, which was at least partially attributed to their high content of black carbon (Lehmann et al. 2003). The high stability of black carbon in soils and its beneficial effect on soil fertility led to the idea that this technology could be used to actively improve poor soils in the humid tropics (Glaser et al. 2001; Lehmann and Rondon 2006). However, most studies in this context concentrated on extensive production systems, on crops other than rice, and on wood as the source of black carbon. But black carbon can be produced by incomplete combustion from any biomass and it is a by-product of modern technologies for bioenergy production (pyrolysis). © Springer Science + Business Media B.V. 2009.SM Haefele, C Knoblauch, M Gummert, Y Konboon, and S Koyam

Black Carbon from Rice Residues as Soil Amendment and for Carbon Sequestration

On highly weathered soils in tropical and subtropical climates, maintenance of soil organic matter is essential to sustain system productivity and avoid rapid soil degradation. But climatic conditions as well as soil characteristics favor the rapid decomposition of organic matter. However, several recent studies indicated that black carbon, the product of incomplete combustion of organic material, could combine characteristics highly beneficial for soil nutrient dynamics with high stability against chemical and microbial breakdown. Lasting soil amelioration by incorporation of black carbon from wooden plants was proposed based on the beneficial evidence from ?Terra Preta? soils in Western Amazonia. Theoretically, charred crop residues in rice-based systems could serve the same purpose but this hypothesis has never been tested. Within this context, our objectives were to 1) assess possible options for the use of charred rice residues, to 2) test the effect of charred rice residues on important soil fertility parameters and rice growth, and 3) to evaluate the effect and stability of charred rice residues in a variety of rice growing environments. Initial investigations showed that charred rice husks are already used in several Asian countries, e.g. in Japan for seed bed preparation of rice and vegetable crops, and in the Philippines for soil amelioration in ornamental plant production. Charring of rice husks in Japan is known as ?Kuntan? and simple techniques for its production are even part of agricultural training courses. First experiments showed that charring rice husks slightly increases the relative carbon content but the weight loss from fresh to charred rice husks is about 70%. Similarly to carbon, the relative concentration of other nutrient elements (e.g., N, P, K, Ca, Mg) is maintained or even increased. Greenhouse studies in pot experiments conducted in the Philippines and northeast Thailand in 2005 showed positive effects of charred rice husks on rice biomass, rice yield, and cation exchange capacity. No increased leaching of organic carbon was observed when charred rice husks were added to the soil. Randomized and replicated field trials including control treatments and +/- inorganic fertilizer treatments were established in a variety of rice-growing environments including irrigated lowlands, rainfed uplands (both in the Philippines), rainfed lowlands (northeast Thailand), and the rice-wheat system (India). In these trials, the quantity of carbon applied equaled about 1.4% in the surface soil layer (0.0 - 0.1 m) or about 16 t carbon per hectare. Converted to biomass, this is equivalent to the crop residues of about 10 to 20 seasons, depending on the system's productivity (including straw and assuming the above mentioned efficiency in black carbon production). In the first cropping season, observed agronomic effects of the charred rice husks were variable and depended on the cropping system and the indigenous soil fertility. Contrary to that, the effects on soil characteristics were more consistent and major effects were an increase of the cation exchange capacity, a decrease of soil bulk density, and a stable increase of soil organic carbon. However, preliminary results strongly suggest that a continuation of the field trials is necessary to better evaluate the long-term treatment effects. If the greater part of the applied black carbon proves to be stable in some or all tested cropping systems, this technology could be an interesting option for carbon sequestration. If used at a large scale, considerable research efforts would be needed to evaluate the various and far-reaching consequences of the proposed technology

Black Carbon from Rice Residues as Soil Amendment and for Carbon Sequestration

On highly weathered soils in tropical and subtropical climates, maintenance of soil organic matter is essential to sustain system productivity and avoid rapid soil degradation. But climatic conditions as well as soil characteristics favor the rapid decomposition of organic matter. However, several recent studies indicated that black carbon, the product of incomplete combustion of organic material, could combine characteristics highly beneficial for soil nutrient dynamics with high stability against chemical and microbial breakdown. Lasting soil amelioration by incorporation of black carbon from wooden plants was proposed based on the beneficial evidence from ?Terra Preta? soils in Western Amazonia. Theoretically, charred crop residues in rice-based systems could serve the same purpose but this hypothesis has never been tested. Within this context, our objectives were to 1) assess possible options for the use of charred rice residues, to 2) test the effect of charred rice residues on important soil fertility parameters and rice growth, and 3) to evaluate the effect and stability of charred rice residues in a variety of rice growing environments. Initial investigations showed that charred rice husks are already used in several Asian countries, e.g. in Japan for seed bed preparation of rice and vegetable crops, and in the Philippines for soil amelioration in ornamental plant production. Charring of rice husks in Japan is known as ?Kuntan? and simple techniques for its production are even part of agricultural training courses. First experiments showed that charring rice husks slightly increases the relative carbon content but the weight loss from fresh to charred rice husks is about 70%. Similarly to carbon, the relative concentration of other nutrient elements (e.g., N, P, K, Ca, Mg) is maintained or even increased. Greenhouse studies in pot experiments conducted in the Philippines and northeast Thailand in 2005 showed positive effects of charred rice husks on rice biomass, rice yield, and cation exchange capacity. No increased leaching of organic carbon was observed when charred rice husks were added to the soil. Randomized and replicated field trials including control treatments and +/- inorganic fertilizer treatments were established in a variety of rice-growing environments including irrigated lowlands, rainfed uplands (both in the Philippines), rainfed lowlands (northeast Thailand), and the rice-wheat system (India). In these trials, the quantity of carbon applied equaled about 1.4% in the surface soil layer (0.0 - 0.1 m) or about 16 t carbon per hectare. Converted to biomass, this is equivalent to the crop residues of about 10 to 20 seasons, depending on the system's productivity (including straw and assuming the above mentioned efficiency in black carbon production). In the first cropping season, observed agronomic effects of the charred rice husks were variable and depended on the cropping system and the indigenous soil fertility. Contrary to that, the effects on soil characteristics were more consistent and major effects were an increase of the cation exchange capacity, a decrease of soil bulk density, and a stable increase of soil organic carbon. However, preliminary results strongly suggest that a continuation of the field trials is necessary to better evaluate the long-term treatment effects. If the greater part of the applied black carbon proves to be stable in some or all tested cropping systems, this technology could be an interesting option for carbon sequestration. If used at a large scale, considerable research efforts would be needed to evaluate the various and far-reaching consequences of the proposed technology

Effects and fate of biochar from rice residues in rice-based systems

Abstract not availableS.M. Haefele, Y. Konboon, W. Wongboon, S. Amarante, A.A. Maarifat, E.M. Pfeiffer and C. Knoblauc

The effect of toposequence position on soil properties, hydrology, and yield of rainfed lowland rice in Southeast Asia

large proportion of rainfed lowland rice in Southeast Asia is grown in gently sloping areas along toposequences with differences in elevation of a few meters. These small differences in elevation can lead to differentiation in soil properties and hydrological conditions, which in turn may affect crop performance and yield. It may be appropriate to replace blanket crop management recommendations in rainfed areas with toposequence-specific management recommendations. However, thorough statistical analyses of the relationships between toposequence position and field and crop conditions are lacking. In this paper, we statistically analysed the effect of toposequence position on soil properties, hydrological conditions, yield, and yield increase due to weed control and/or fertilizer management in rainfed areas in four villages in Indonesia and Thailand each in 2000¿2002. Differences were substantial in field hydrology (average depth of ponded surface water and of groundwater, number of days without ponded surface water), exchangeable K, organic C, and clay content depending on toposequence position. There were also differences in other soil properties, including N, P, CEC, pH, sand, silt, bulk density, yield, and the magnitude of yield increase due to intensive weed control and/or recommended fertilizer application, but these effects were not consistent across countries, seasons, and years. The hypothesis that toposequence position would be a useful recommendation domain for weed control and fertilizer recommendations was not supported by our statistical results. The reasons why toposequence position has an inconsistent statistical effect could be (1) that the variability of the field conditions is larger among villages than among toposequence positions, and/or (2) that farmers already respond to differences in field conditions in their prevalent management practices, thus masking the effects of toposequence-specific variation on yield. Our findings suggest that despite the large toposequence effects on soil nutrient and water availability, weed and fertilizer management recommendations should be field-specific and time-specific rather than toposequence-specifi