The effects of compost application on soil carbon sequestration potential and carbon budget of a tropical sandy soil was studied. Greenhouse gas emissions from soil surface and agricultural inputs (fertiliser and fossil fuel uses) were evaluated. The origin of soil organic carbon was identified by using stable carbon isotope. The CO2, CH4 and N2O emissions from soil were estimated in hill evergreen forest (NF) plot as reference, and in the corn cultivation plots with compost application rate at 30 Mg ha−1 y−1 (LC), and at 50 Mg ha−1 y−1 (HC). The total C emissions from soil surface were 8·54, 10·14 and 9·86 Mg C ha−1 y−1 for NF, HC and LC soils, respectively. Total N2O emissions from HC and LC plots (2·56 and 3·47 kg N2O ha−1 y−1) were significantly higher than from the NF plot (1·47 kg N2O ha−1 y−1). Total CO2 emissions from fuel uses of fertiliser, irrigation and machinery were about 10 per cent of total CO2 emissions. For soil carbon storage, since 1983, it has been increased significantly (12 Mg ha−1) under the application of 50 Mg ha−1 y−1 of compost but not with 30 Mg ha−1 y−1. The net C budget when balancing out carbon inputs and outputs from soil for NF, HC and LC soils were +3·24, −2·50 and +2·07 Mg C ha−1 y−1, respectively. Stable isotope of carbon (δ13C value) indicates that most of the increased soil carbon is derived from the compost inputs and/or corn biomass. Copyright © 2011 John Wiley & Sons, Ltd.
This study investigated the effects of O 3 on growth, yields and physiological characteristics of Thai Jasmine rice cultivars. Rice was exposed to O 3 for 7 h day −1 in a closed chamber for 113 days, beginning from seedling until harvest. O 3 concentration in each chambers was controlled at 0 ppb, 50 ppb, 100 ppb, 150 ppb and at the ambient level. Effects of O 3 on leaf area index (LAI) became obvious at maturity when LAI significantly decreased in the treatments under elevated O 3 concentrations. Results in shoot biomass indicated that shoot length was more affected by O 3 than shoot dry weight. Root length rather than dry weight was significantly reduced in all cultivars. The most severe damage of O 3 was found in photosynthetic components, namely chlorophyll and carotenoid contents, and rate of net photosynthesis. Yield components were also strongly affected by O 3 . The highest reduction in filled seed per ear was found in the Pathumthani 1 cultivar by 78% when it was exposed to 150 ppb O 3 compared to the control (0 ppb). Similarly, 100-grain weight was also reduced as much as 12.3% in this cultivar.
Water deficit is a major limiting condition for adaptation of maize in tropical environments. The aims of the current observations were to evaluate the kernel water relations for determining kernel developmental progress, rate, and duration of kernel filling, stem reserve mobilization in maize. In addition, canopy temperature, cell membrane stability, and anatomical adaptation under prolonged periods of pre- and post-anthesis water deficit in different hybrids was quantified to support observations related to kernel filling dynamics. In this context, two field experiments in two consecutive years were conducted with five levels of water regimes: control (D1), and four water deficit treatments [V10 to V13 (D2); V13 to V17 (D3); V17 to blister stage (D4); blisters to physiological maturity (D5)], on three maize hybrids (Pioneer 30B80, NK 40, and Suwan 4452) in Expt. 1. Expt. 2 had four water regimes: control (D1), three water deficit treatments [V10 to anthesis (D2); anthesis to milk stage (D3); milk to physiological maturity (D4)], and two maize hybrids (NK 40 and Suwan 4452). Water deficit imposed at different stages significantly reduced maximum kernel water content (MKWC), kernel filling duration (KFD), final kernel weight (FKW), and kernel weight ear–1 while it increased kernel water loss rate (KWLR), kernel filling rate (KFR), and stem weight depletion (SWD) across maize hybrids in both experiments. The lowest MKWC under water deficit was at D3 in both experiments, indicating that lower KFR results in lowest FKW in maize. Findings indicate that the MKWC (R2 = 0.85 and 0.41) and KFR (R2 = 0.62 and 0.37) were positively related to FKW in Expt. 1 and 2, respectively. The KFD was reduced by 5, 7, 7, and 11 days under water deficit at D3, D4 in Expt. 2 and D4, D5 in Expt. 1 as compared to control, respectively. Water deficit at D5 in Expt. 1 and D4 in Expt. 2 increased KWLR, KFR, and SWD. In Expt. 2, lower canopy temperature and electrical conductivity indicated cell membrane stability across water regimes in NK 40. Hybrid NK 40 under water deficit had significantly higher cellular adaptation by increasing the number of xylem vessel while reducing vessel diameter in leaf mid-rib and attached leaf blade. These physiological adjustments improved efficient transport of water from root to the shoot, which in addition to higher kernel water content, MKWC, KFD, KFR, and stem reserve mobilization capacity, rendered NK 40 to be better adapted to water-deficit conditions under tropical environments.
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