The influence of residue quality on soil organic C (SOC) retention has been called into question. A field experiment in Northeast Thailand, in which contrasting quality organic residues were applied yearly for 13 yr, was used to determine quantities, locations, and stability of SOC in the soil matrix and identify residue quality parameters affecting SOC stabilization in a tropical sandy‐textured soil. Total organic C (TOC) content was highest in intermediate‐quality tamarind (Tamarindus indica L.) at 3.58 g kg−1 (intermediate N, lignin, and polyphenol contents), followed by groundnut (Arachis hypogaea L.) stover at 2.63 g kg−1 (high N), dipterocarp (Dipterocarpus tuberculatus Roxb.) at 2.63 g kg−1 (low N, high lignin and polyphenols), and rice (Oryza sativa L.) straw at 1.77 g kg−1 (high cellulose). Microaggregates (Mi) (0.053–0.25 mm) stored the highest C content (34–49% of TOC), with tamarind having the highest C content. Carbon in large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), and free organic matter (>0.053 mm) was significantly positively correlated with C, lignin, and polyphenols. Carbon in microaggregates and fine particles (<0.053 mm) was significantly negatively correlated with C/N ratio. Soil fraction C was negatively correlated with residue cellulose contents. Protected C lost through mineralization in Mi was lower in tamarind (7% Mi‐C) followed by groundnut (9.5%), dipterocarp (17.7%), and rice straw (18.6%). It was significantly positively correlated with cellulose and C/N ratios but negatively correlated with N contents. Possible mechanisms of aggregate formation are based on microbial synthesis of both persistent (humic substances) and transient (polysaccharides) binding agents as influenced by residue quality. The results showed clearly that residue quality plays an important role in SOC accumulation in tropical sandy soils.

The objectives of this study were to investigate decomposition patterns and soil organic matter (SOM) accumulation of incorporated residues (10 Mg ha -1 year -1 ) of different quality, and identify microbiological parameters sensitive to changes in SOM dynamics, in a 13-year-old field experiment on a sandy soil in Northeast Thailand. Mass loss was fastest in groundnut stover (high N), followed by rice straw (high cellulose) and tamarind (intermediate quality), and slowest in dipterocarp (high lignin and polyphenol) following a double exponential pattern. The decomposition rate k 1 (fast pool) was positively correlated with cellulose (r = 0.70*) while k 2 (slow pool) was negatively related to lignin (r = -0.85***) and polyphenol (r = -0.81

International audienceAdequate water management is required to im- prove the efficiency and sustainability of agricultural sys- tems when water is scarce or over-abundant, especially in the case of land use changes. In order to quantify, to pre- dict and eventually to control water and solute transport into soil, soil hydraulic properties need to be determined pre- cisely. As their determination is often tedious, expensive and time-consuming, many alternative field and laboratory tech- niques are now available. The aim of this study was to de- termine unsaturated soil hydraulic properties under different land uses and to compare the results obtained with differ- ent measurement methods (Beerkan, disc infiltrometer, evap- oration, pedotransfer function). The study has been realized on a tropical sandy soil in a mini-watershed in northeastern Thailand. The experimental plots were positioned in a rub- ber tree plantation in different positions along a slope, in ruzi grass pasture and in an original forest site. Non-parametric statistics demonstrated that van Genuchten unsaturated soil parameters (Ks, α and n) were significantly different ac- cording to the measurement methods employed, whereas the land use was not a significant discriminating factor when all methods were considered together. However, within each method, parameters n and α were statistically different ac- cording to the sites. These parameters were used with Hy- drus1D for a 1-year simulation and computed pressure head did not show noticeable differences for the various sets of parameters, highlighting the fact that for modeling, any of these measurement methods could be employed. The choice of the measurement method would therefore be motivated by the simplicity, robustness and its low cost

A field experiment was conducted at the experimental farm of Khon Kaen University in 2001. The objectives of this study were to investigate growth, yield and yield components of corn, peanut, soybean and mungbean under intercropping and single cropping, as well as to assess the land use efficiency. Yield and yield components of corn was unaffected by intercropping system. In legume crops; peanut, soybean and mungbean, intercropping systems reduced the leaf area and top dry weight per plant as compared with single cropping. Grain yield of peanut, soybean and mungbean was reduced by 28%, 39% and 51 %, respectively, as compared with single cropping. The pod number per plant was the most affected by intercropping among the yield components. However, corn-legume intercropping increased land use efficiency by 48% to 66% depending on legume species. Corn-peanut intercropping gave the highest land use efficiency. The effects of light penetration and nutrient competition are discussed.

No abstract

Problem statement:The saline soil in Northeast Thailand is caused by saline groundwater rise in unsaturated zone to accumulate as salt at soil surface. Approach: This problem had been exacerbated in the last few decades by human activities e.g., deforestation and salt mining. This salinity problem can be solved by capillary rise control of saline groundwater flow. Results: The soil water retention curve formulation was essential for the control procedure design. In this study, the soil water retention curves of saline soil samples were derived by the hanging column and pressure plate apparatus techniques. The hysteresis of the curves together with air and water entry values were scrutinized from the primary wetting and drying retention curves. Conclusion: The experimental results showed that the degree of hysteresis varies with the air entry value of the soil. The new finding can be very useful in modeling for salinity control.

Organic amendments are believed to help increase the soil carbon storage and therefore improve soil quality, which may be important in the context of climate change. However, the added value of organic amendments for farmers must be clearly demonstrated in order to convince them of the utility of their use. The aims of this study were: (i) to investigate the impact on maize of compost and vermicompost combined with two levels (negligible and significant) of plant water stress; and (ii) to determine how the organic amendments affected the soil’s physical properties and maize productivity. Water stress levels were imposed by controlling the matric potential of soil columns in which cultivated soil characteristics was mimicked (10 cm topsoil with organic amendments, above a 50 cm subsoil without any inputs containing the majority of the roots). Plant and soil characteristics were monitored daily for 70 days. Our results show that the use of organic amendments is profitable for farmers as: (i) maize performances were increased in both moisture regimes; and (ii) the improvement was particularly striking in terms of yield. No additional benefits were measured when using vermicompost instead of compost. The data suggest that the improvement in plant characteristics did not result from increased water storage in the soils with organic amendments, but rather from better access to the water, resulting in faster root development in the macroporosity of the amended soils.

The objectives of this research were to investigate the effect of rice straw management and application of different types of organic fertilizer on growth and yield of dry direct-seeded rice grown under rainfed conditions. The experiment was conducted in a farmer's field at Muang Yai village, Khon Kaen province in 2005. A split-plot design was used, with the main plot under rice straw management (incorporating into the soil and burning), and sub-plots by type of organic fertilizer (green manure, cattle manure and powder organic fertilizer) and one plot under no-fertilizer application. It was found that rice straw incorporated into the soil had no significant effect on grain yield when compared with the effect of burning. Organic fertilizer of cattle manure and powder organic fertilizer significantly increased grain yield over that of green manure and no-fertilizer application.