V. Limpinuntana

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.

Land-Use Sustainability of Composite Swiddening in the Uplands of Northern Vietnam: Nutrient Balances of Swidden Fields during the Cropping Period and Changes of Soil Nutrients over the Swidden Cycle

This study examined the sustainability of the swidden component of the composite swiddening system practiced by the Tay ethnic minority in Tat hamlet, Hoa Binh province in Northern Vietnam. This farming system is thought to be suitable for the uplands where land degradation is a serious problem. The common swidden rotation of two years of rice, two years of cassava and five years of bush-tall grass fallow was evaluated for the extent of land degradation during the cropping period by nutrient balance analysis, and for soil nutrient status throughout the swidden cycle through soil analysis. Four fields representing the individual years of cropping and three fields representing the first, the third and the fifth years of bush-tall grass fallow were selected for field measurements. Nutrient balance analysis indicated substantial losses of all major nutrients, particularly K, in all cropping years. Soil analysis also showed a decline in soil fertility during the cropping period and a partial restoration of soil fertility during the fallow period. However, only five years of bush-tall grass fallow was not sufficient to restore the original level of soil fertility. Thus, swidden fields in Tat hamlet are degrading, posing a serious threat to their land-use sustainability.

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

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

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

Rooting patterns of four crop legumes in response to seed-placement depths in the dry season

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.

IS DEEP SOWING BENEFICIAL FOR DRY SEASON CROPPING WITHOUT IRRIGATION ON SANDY SOIL WITH SHALLOW WATER TABLE

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.

Fertiliser strategies for improved nutrient use efficiency on sandy soils in high rainfall regimes

Abstract On sandy paddy fields, key factors for successful crops in the dry season without irrigation are a shallow water table and practices such as deep seed-placement but only some legume species are adapted to such conditions. To understand the adaptation of legume species to deep seed-placement over shallow water tables, we studied their rooting patterns on two sandy soils. Cowpea (Vigna unguiculata), mungbean (Vigna radiata), peanut (Arachis hypogaea) and soybean (Glycine max) seeds were sown shallow (∼5 cm) or deep (∼15 cm) in deep sandy soils after harvesting rice in two shallow water table locations in north-east Thailand. The legumes depended mainly on capillary water rising from the water table and none experienced water deficit throughout the growing season. Generally, deeper seed-placement decreased overall root dry weight, but it increased the root surface area to weight ratio. Deep seed-placement promoted a greater fraction of root growth into the subsoil for cowpea (86–99% of total root length), mungbean (61–93% of total root length) and peanut (78–98% of total root length) where the soil contained more water throughout the growing season. Moreover, deep seed-placement at the site with the lower water table promoted deeper penetration of roots of cowpea (∼20 cm deeper), mungbean (∼20–40 cm deeper) and peanut (∼20–40 cm deeper) which improved water access, especially late during the growing season when topsoils dried to close to wilting point. Unlike other species, the soybean rooting pattern did not respond much to seed-placement depths, or soil moisture.

Mixing groundnut residues and rice straw to improve rice yield and N use efficiency

Deep sowing (15 cm) on sands in the dry season is a practice used in post-rice sowing of legumes without irrigation, designed to increase moisture access for germination, growth and crops yield. However, with such deep sowing there can be a penalty for emergence and growth if there is abundant water stored in the upper soil profile during the growing season. Hence, there is a need to define the soil water regimes under which deep sowing is advantageous for different legumes. To investigate the adaptation of legume crop species to deep sowing, we studied their emergence, growth and yield on three deep soils (3-16% clay) with shallow water tables during two years in northeast Thailand. At site 1 and 2, peanut, cowpea, mungbean and soybean were sown shallow (~5 cm) or deep (~15 cm). At site 3, only cowpea and peanut were shallow or deep sown. Shallow water tables maintained soil water content (0-15 cm) above permanent wilting point throughout the growing season. Deep sowing of all legumes delayed emergence by 3-7 days at all locations. Shoot dry weight of legumes after deep sowing was mostly similar or lower than weight after shallow sowing. Yield and harvest index of legumes did not differ meaningfully among sowing depths. Therefore, deep sowing was not beneficial for dry season cropping without irrigation when there was a shallow water table and sufficient water for crop growth throughout soil profiles in the growing season. Taken together with previous studies, we conclude that shallow rather than deep sowing of legumes was preferred when the soil water content at 0-15-cm depth remained higher than permanent wilting point throughout the growing season due to shallow water table.