Supplies of soil amendments and fertilizers are major constraints to increasing crop productivity in rural Cambodia. In order to test and compare potential soil amendments, we examined the effects of biochar from rice (Oryza sativa L.) husk and Siam weed (Chromolaena odorata), with and without fertilizer on plant growth and soil properties. Tomato (Solanum lycopersicum L.) was grown on loamy sand (clay-silt-sand = 9-10-81), with a pH of 7.7, and exposed to the following seven treatments: no input (control), rice husk biochar (RB), rice husk biochar + compost (RBcom), rice husk biochar + NPK (15:15:15) fertilizer (RBchem), C. odorata biochar (CB), C. odorata biochar + compost (CBcom), and C. odorata biochar + NPK (CBchem). The results showed that only CBchem provided significantly greater fresh root weight (+58%) and total fresh biomass (+166%) than control. RB, RBchem, and RBcom did not increase all the parameters on plant growth and soil properties. The soil pH of CB (7.8), CBcom (7.9), and CBchem (7.7) were significantly enhanced as compared to control (7.3). Compared to CBchem, CBcom caused greater increases in soil pH, EC, available P, available N, exchangeable Ca, and exchangeable K, although those increases were not statistically significant. Hence, C. odorata biochar was considered as a nutrient-rich amendment that had a high amount of N, P, Ca, Mg, and K after the charring process, and contributed to improve plant growth.

Erianthus arundinaceus (Retz.) Jeswiet collected in Japan is a promising breeding material for sugarcane improvement because of its high biomass productivity and overwintering ability in temperate areas. However, its early heading behavior prevents intergeneric crossing with sugarcane under natural day length. The aim of this study is to develop a more effective delayed heading technique for the Japanese E. arundinaceus to achieve intergeneric crossings with sugarcane. Using the earliest and the latest heading accessions JW630 and JW4, respectively, as experimental materials, we evaluated the effects on their delayed heading by photoperiodic treatment (PT)—namely long-day and short-day treatments from 22 June to 23 August and from 24 August to 8 November, respectively—with different ratooning times (April, June and July). The effects on delayed heading were enhanced when PT was applied to the later-ratooning materials. The heading was delayed by –1 to 5 days in JW630 and 8 days in JW4 with the April-ratooning, and by 5 to 9 days in JW630 and 12 to 13 days in JW4 with the June-ratooning, and by 18 to 21 days in JW630 and 16 to 19 days in JW4 with the July-ratooning, respectively. As a result, headings could be delayed in JW630 and JW4 until mid- and late November, respectively, at maximum. Since pollen-germination rates in PT plots exceeded 25%, they could be used as a male parent for crossing with sugarcane. JW630 and JW4 were crossed with 40% and 80% sugarcane breeding materials, respectively, using this technology.

In response to the tightening supplies and growing demands for water on a global scale, the International Rice Research Institute has attempted to diffuse a water-saving technology called alternate wetting and drying irrigation (AWD) for rice farming in Asian countries. This study assessed the compatibility of AWD with local agriculture, based on field surveys in An Giang Province (AG), which is located in the Mekong Delta of Vietnam. Interviews with the local government staff that is responsible for AWD diffusion in AG indicated that farmers who used AWD realized not only water-saving effects, but also improvements in rice yield and growth. For instance, rice farming in the Mekong Delta has always suffered from culm lodging due to the flood plain location; however, farmers realized decline of culm lodging through AWD, and hence these additional benefits will help to further diffuse AWD. Moreover, these interviews illuminate that AWD can be used in certain natural, agro-engineering, and social settings, because it’s an irrigation technology that requires precise water level control. For instance, higher-lying paddy fields tend to dry up earlier due to higher levels of percolation and seepage, while lower-lying fields are difficult to drain; therefore, mid-lying fields are best suited to AWD. This study highlights the importance of compatibility between AWD and the local agriculture in the diffusion process based on qualitative surveys, which should be quantitatively verified with statistical data and satellite images on a wider scale.

Sugarcane has been cultivated across large areas of Negros Island, the Philippines. Clean groundwater is essential for island residents, yet high concentrations of nitrate nitrogen have sometimes been observed. Thus, it is important to implement the appropriate management of nitrogen fertilizers by farmers to reduce the nitrogen load to groundwater from sugarcane production. In particular, nitrogen applied during the early growth stage of sugarcane is considered to be only slightly absorbed by the plant, and a large portion of the nitrogen is leached into groundwater. It is necessary to clarify the actual state of nitrogen fertilizer application to develop appropriate fertilizer application management. In this study, therefore, a survey of farmers was conducted to clarify the actual state of nitrogen application. The results showed that (1) many farmers applied more nitrogen than the standard nitrogen application rate developed in the Philippines, and a relationship between the nitrogen application rate during the cultivation period and the sugarcane yield in new planting was not observed; (2) the frequency of fertilization, the timing of the first nitrogen application, and the application rate differed by farmer; (3) many farmers applied a large amount of nitrogen during the early growth stage of sugarcane, and a relationship between the nitrogen application rate during that stage and the yield was not observed. To reduce nitrogen load to groundwater from sugarcane cultivation, it is imperative to clarify the appropriate timing of nitrogen applications and the application rate of each timing and to disseminate this information to sugarcane farmers.

To stabilize or increase yield in rainfed paddy fields in Surin province, northeast Thailand, the factors controlling yield were investigated. The undulating topography is characteristic of the region causing differences in soil properties and water availability at low and high elevations. Soil samples were collected at 52 plots from two selected sites with undulating topography in Surin province. Soil physico-chemical properties (e.g., texture, available phosphorus (P), and available potassium (K)) and hydrological conditions (e.g., hydraulic conductivity and available water capacity (AWC)) were determined. Rice grain yield and relative elevation at each plot were measured. The rice grain yield was 1.8–2.7 t ha^-1, which is in the range of the regional average. The soils were predominated by sandy texture and had low chemical fertility (e.g., low pH, available P and available K). Correlation analysis indicated that the most likely factor that limits yield of jasmine rice was AWC. Chemical properties did not correlate with the yield. The soils at higher elevations with courser texture had lower AWC and would be more vulnerable to drought. The first priority for management of rainfed rice production system to increase yield would be management of water availability.