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Rice (Oryza sativa) is a staple food crop for over half of the world's population. However, drought as a result of climate change has led to increased soil salinity, thereby reducing agricultural potential, especially rice nutritional compositions and biochemical properties. Nevertheless, soil management by using suitable fertilizers might be able to improve rice quality even though these rice samples were grown in soil with a high degree of salinity. This study investigated nutritional compositions, phenolic contents, and antioxidant activities of twenty-five rainfed rice samples in Khao Dawk Mali 105 (KDML105) and Rice Department 15 (RD15) varieties grown in soil with different degrees of salinity. The soil, however, had been improved by the usage of fertilizer at the tillering and booting stages. Results indicated that all rice samples exhibited similar nutrients, total phenolic contents (TPCs), and antioxidant potentials, suggesting that appropriate fertilizer could improve rice qualities. Principle Component Analysis (PCA) and Pearson correlation results suggested that regardless of rice varieties, organic matter (OM) and soil potassium (Ks) showed a very strong positive correlation with protein and minerals (Ca, Na, K, and Fe), while opposite results were observed with soil pH. Moderate to very weak correlations were also observed between soil parameters and TPCs, as well as between soil parameters and antioxidant activities. The received information will be useful for the future development of appropriate fertilizer usage in salt-tolerant rice with particular nutritional quality. [ABSTRACT FROM AUTHOR]

Rubber tree cultivation is presently expanding rapidly into dry subhumid areas. As a consequence, trees face a long dry season. Low growth rates are delaying the start of tapping. The relationship between the growth rate and the soil water availability is not clear. Therefore, we studied the origin of low growth rates. For that we analyzed the relationships between growth, plant water stress, and soil water availability along a toposequence with a soil depth gradient. The plantation of 3-year-old Hevea brasiliensis trees was located in northeast Thailand. Tree circumference, predawn leaf water potential ( p), soil water potential ( s), and micrometeorological parameters were monitored from 2007 to 2010. Results show spatial and temporal variability of growth with a threshold value of leaf water potential of −0.4 MPa for growth. This leaf water potential threshold was not associated with very dry soils as soil water potentials were higher than −0.05 Mpa. But the leaf water potential threshold was associated with a high air vapor pressure deficit higher than 3-4 kPa. Leaf water potential decreased when the soil at the bottom of the slope was saturated in the rainy season. These results provide, for the first time, evidence that soil water shortage is unexpectedly not the main cause of low growth rates. Dry air in the dry season and waterlogging in rainy season are major constraints. [ABSTRACT FROM AUTHOR]

The expansion of rubber cultivation into drought prone areas calls for innovative management to increase the drought resistance of the trees. The competition for water exerted by an intercrop in the upper soil layers will likely stimulate the growth of young rubber tree roots into deeper soil layers where water availability is more stable. This study examined the effects of a legume (Pueraria phaseoloides) and a grass (Vetiveria zizanoides) intercrop, on the fine root traits of young rubber trees (Hevea brasiliensis Müll. Arg.) established along a toposequence covering a range of soil depths in northeast Thailand. Two plots with and without the intercrops were set up in a 3-year-old rubber plantation. Tree girth, mortality rate, nutrient content in the leaves, predawn leaf water potential, and soil water content profiles were monitored over four successive years. Fine root length density, specific root length, fine root biomass, and fine root diameter of the rubber trees were measured in the fourth year. In shallow soils, the trees with the legume intercrop had a higher growth rate, a higher leaf nutrient content, and a higher fine root length density in the deepest soil layers than the controls, supporting the hypothesis of an adaptive root response, increasing drought resistance. However, the trees with the grass intercrop did not show this effect. In deep soils, specific root length was highest without the intercrops, and the soil water profile and predawn leaf water potential suggested that trees with intercrops benefited from increased water extraction below 110 cm depth. We showed, for the first time, that rubber tree root traits can be manipulated through intercropping to improve drought resistance. However, our results suggest intercropping might not reduce risks of tree mortality caused by drought in the shallowest soils of the subhumid area of northeast Thailand. [ABSTRACT FROM AUTHOR]