B. Toomsan

Soil organic matter and nitrogen transformation mediated by plant residues of different qualities in sandy acid upland and paddy soils.

Organic matter management is believed to solve many of the chemical and physical problems of coarse-textured, low fertility soils of NE Thailand. The influence of different plant residues available in this area on soil C and N dynamics in upland (Oxic Paleustult) and lowland (Aeric Paleaquult) soils was tested. Residues included groundnut (upland) or Sesbania rostrata stover (lowland), rice straw, Tamarindus indica and Dipterocarpus tuberculatus leaves applied at 10 t ha-1 (dry matter). For the former three residues additional application rates of 20 t ha-1 were included as well as a mixture (50:50) of groundnut/ Sesbania - rice straw treatment. Groundnut stover and Sesbania had C:N ratios 17%) and polyphenol (>4.5%) contents. These latter residues, despite slow decomposition, apparently resulted in only moderate soil C ( 1 mm). Thus the mixture of groundnut/ Sesbania with straw was among those residue treatments that led to the highest soil C ( Sesbania with rice straw with a high C:N ratio residue N mineralization could be delayed and prolonged, improving potentially the synchrony of N release and plant demand. Additions of dipterocarp and tamarind resulted in an initial N immobilization phase and net mineral N release remained low thereafter. Dynamics of microbial biomass N were closely related to N mineralization and immobilization cycles in both upland and lowland experiments. Residue N concentration was the most significant factor controlling N release in both systems. While extractable polyphenols exhibited a significant influence on N release in upland conditions their effect was not evident in the lowland.

Biological N2 fixation and residual N benefit of pre-rice leguminous crops and green manures

A pre-rice crop experiment, including groundnut, mung bean ( Vigna radiata ), Sesbania rostrata , and a mixture of Sesbania and multipurpose cowpea ( Vigna unguiculata ) was conducted on a characteristic sandy soil of NE Thailand. The Sesbania -cowpea intercrop gave a similar total plant biomass as the Sesbania green manure alone (7 t ha-1) but with the advantage of yielding an edible product. The direct economic yield of cowpea was 1.3 t ha-1 green beans and greater than that achieved with groundnut or mung bean. The Sesbania -cowpea combination also enhanced rice yields by 0.8 t ha-1. The benefits in rice production were similar to the Sesbania green manure alone but surpassed the yields with the other grain crops or urea fertilizer of 30-60 kg N ha-1. Sesbania dry matter production increased with increasing planting density. The resulting variation in plant quality, e.g. lignin, however, was low. Rice responses to treatments were more related to the total residue N yields than to changes in plant quality. Apart from mung bean (25%) the pre-rice leguminous crops were able to obtain a considerable (>39%) proportion of their N from N2 fixation. The green manure Sesbania however fixed a larger proportion (79-89%) of its N than the grain crops (25-62%). This led not only to high amounts of N2 fixed by Sesbania but together with a N harvest index of zero yielded a large systems N benefit. With grain legumes this benefit was moderated by the N export in harvestable products. In the case of mung bean this may even result in effective soil N mining. Residue N use efficiency varied between 19-29% and was similar to that obtained from a single application of chemical N fertilizer (17-28%). For the farmer the Sesbania -cowpea intercrop option seems thus the most promising one not only regarding rice yield benefits but also in terms of soil fertility enhancement and generation of edible products.

Nitrogen fixation (15N dilution) with soybeans under Thai field conditions

In the infertile sandy soils of northeast Thailand, field experiments were conducted to evaluate the effects on rates of biological nitrogen fixation (BNF) of inoculating soybeans with selected strains of Bradyrhizobium japonicum and adding herbicides. Inoculating soybean seeds with effective B. japonicum strains increased the acetylene reduction by nodulated root systems, and increased the nodule numbers and dry weights associated with soybean roots. The amounts of Nz fixed, as measured by N-15 isotope dilution methods, were also increased by adding the B. japonicum. Inoculation of soybeans with a nif strain of B. japonicum resulted in increased nodule weights and numbers, but did not increase the acetylene reduction rates or the amounts of Nz fixed. There was a significant straincultivar interaction. Application of metolachlor, alachlor, fluazifop butyl or sethoxydim did not reduce the levels of Nz fixed by B. japonicum in association with soybeans, but paraquat did significantly reduce the Nz fixed by the inoculated plants.

An analysis of the economic values of novel cropping systems in N. E. Thailand and S. Sumatra

Abstract The use of food-crop intercropping, hedgerow intercropping and secondary or cover cropping to increase incomes of resource-poor farmers in South East Asia was investigated. Since all systems improve conservation of nutrients and most give extra marketable produce, they were expected to increase farm profitability. On upland farms in Lampung, South Sumatra, both inter- and secondary crops were found to improve yields compared with cassava monocropping and thus the income derived from growing cassava or rice with maize. These increases were equivalent to between 70 and 440 US dollars per hectare. An economic analysis of the lowland rice-producing systems in North East Thailand suggested that with the exception of growing cowpea, the use of pre-rice cover crops was not profitable despite a substantial increase in rice yield, because the additional labour cost more than the additional income was worth. A benefit of leguminous crops, however, can be the extra marketable product. Groundnut in Indonesia and cowpea in Thailand gave an attractive extra US

Sweet Sorghum and Upland Rice: Alternative Preceding Crops to Ameliorate Ethanol Production and Soil Sustainability Within the Sugarcane Cropping System

400–1150 total income increase per hectare per year (i.e. extra yield of the main food crop plus extra marketable produce from the secondary crop) even after the additional costs were deducted. Hedgerow intercropping gave smaller profit margins of about US

Evaluation of Groundnut Stover Management Strategies in a Legume-Rice Rotation

90. Although both hedgerow intercropping and secondary cropping represent a considerable investment of labour by farmers, this investment may be more feasible than paying for fertilizer on credit. On balance the most attractive option tested was the use of a leguminous secondary crop, e.g. groundnut or multipurpose cowpea, within the food crop cycle.

Relationship between Biomass Production and Nitrogen Fixation under Drought-Stress Conditions in Peanut Genotypes with Different Levels of Drought Resistance

The objective of this study was to assess the effect of preceding crops (soybeans, sunn hemp, upland rice, and sweet sorghum) on the succeeding sugarcane yield, total bioethanol production, and soil chemical properties within the sugarcane cropping system. Treatments with upland rice and sweet sorghum provided the greatest increase in soil available P, compared to uncultivated land (control) at the final sampling, preceding the sugarcane harvest. Treatments effects were not significantly different for soil organic matter. At sugarcane harvest, the upland rice treatment provided the highest cane yield compared to the unplanted land, yet was not significantly higher than the yield of the sweet sorghum treatment. The highest sugarcane ethanol yields were observed in the sweet sorghum–sugarcane and upland rice–sugarcane treatments. However, the total ethanol yield in both preceding and succeeding crops was found to be highest in the sweet sorghum treatment, followed by the upland rice treatment. Upland rice proved to be most suitable for farming systems which emphasized food security, whereas sweet sorghum was most desirable for farming systems which emphasized alternative biofuel production. Both crops improved the sustainable production of soil and sugarcane.

Biochar characteristics and application rates affecting corn growth and properties of soils contrasting in texture and mineralogy.

ABSTRACT Groundnuts grown after rice often lead to a gap of 1–3 months between legume harvest and planting of the next rice crop in many parts of Southeast Asia. To identify the best stover management strategy in such systems, the effect of methods of application (surface application vs incorporation), complementary mineral (NPK) additions and time of incorporation of groundnut stover on growth of rice KDML 105 and on decomposition (litter bag) was assessed. Groundnut provided 7500 kg ha−1 of stover corresponding to a recycling of 100 kg N ha−1, 10 kg P ha−1 and 74 kg K ha−1 which resulted in higher seed yield of the succeeding rice compared with removing stover from the field. Initially, low leaf area index where stover was incorporated 6 and 13 days before transplanting indicated a negative effect of decomposing stover; however, rice plants fully recovered subsequently. N application at panicle initiation did not have a significant effect on dry matter yields, although it increased seed N contents, especially those of the early stover application treatments. Neither N application nor omission of PK fertilizer at rice transplanting had any significant effect on rice growth suggesting groundnut stover is an effective basal fertilizer. N accumulation in rice increased with decreasing time of stover application before rice transplanting probably associated with rapid N (and K) release from residues. Storage of residues and application shortly before rice transplanting led to a better recycling of N but the associated seed yield gains were small and probably not sufficient to make it an attractive alternative for farmers.