Alleviating an Acid Sulfate Soil Cultivated to Rice (Oryza sativa) Using Ground Magnesium Limestone and Organic Fertilizer

Rice yield on acid sulfate soils in Malaysia is very low, presumably due to AI and/or Fe toxicity. This study wasconducted to ameliorate an acid sulfate soil in the Kemasin-Semerak Integrated Agricultural Development Project, located in Kelantan, Peninsular Malaysia, for rice cultivation. Rice variety, MR 219, was used as the test crop. Treatment included the use of various rates of ground magnesium limestone (GML), with or without an organic fertilizer. This acid sulfate soil had an initial pH of < 3.5 at depth below 45 cm. Exchangeable AI in the soil was high, especially in the subsoil. The first crop of rice was disturbed by floods. The result for the 2"d crop showed a promising trend; applying 4 t GMUha in combination with an organicfertilizer, the topsoil pH had increasedfrom 3.95 to 4.21, increasing the exchangeable Ca and Mgfrom 1.58 and 0.48 cmol/kg soil to 2.57 and O. 79 cmol/kg soil, respectively. In this treatment, the rice yield was 7.5 tlha, which was much higher than that produced by farmer's practice of about 2 tlha. The increase in yield was due to the combined effects of increasing pH and exchangeable Ca and Mg and of lowering AI and Fe concentration in the soil solution

Modelling the partitioning of radiation capture and evapotranspiration in intercropping systems

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN042186 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Parameterization of the Farquhar-von Caemmerer-Berry C3 photosynthesis model for oil palm

The Farquhar-von Caemmerer-Berry C3 photosynthesis (FvCB) model is used to model photosynthesis of oil palm. However, some model parameters and their temperature dependencies are not known for oil palm. Hence, the aim of this study was to determine the intercellular photocompensation point (Ci*), rate of leaf day respiration in the light (Rd), the chloroplastic photocompensation point (Γ*), mesophyll conductance (gm), maximum rates of Rubisco carboxylation (Vcmax) and electron transport (Jmax), triose phosphate utilization (TPU) and their temperature dependencies between 25 and 40°C in oil palm. Using leaf gas-exchange and chlorophyll fluorescence measurements, parameters such as Rd, Ci*, Γ*, gm, Vcmax, Jmax, and TPU were determined for oil palm. The parameters Ci*, Rd, Γ*, gm, and Vcmax responded to temperature exponentially without thermal deactivation. In contrast, Jmax and TPU responded to temperature exponentially up to 38°C before decreasing slightly at 40°C. Taken altogether, this study determined some key FvCB model parameters and their temperature dependencies for oil palm. This paves the way for more accurate modelling of photosynthetic carbon assimilation in oil palm particularly under future elevated temperatures and CO2 concentrations

Modelling the partitioning of evapotranspiration in a maize-sunflower intercrop

The primary purpose of this study was to model the partitioning of evapotranspiration in a maize-sunflower intercrop at various canopy covers. The Shuttleworth-Wallace (SW) model was extended for intercropping systems to include both crop transpiration and soil evaporation and allowing interaction between the two. To test the accuracy of the extended SW model, two field experiments of maize-sunflower intercrop were conducted in 1998 and 1999. Plant transpiration and soil evaporation were measured using sap flow gauges and lysimeters, respectively. The mean prediction error (simulated minus measured values) for transpiration was zero (which indicated no overall bias in estimation error), and its accuracy was not affected by the plant growth stages, but simulated transpiration during high measured transpiration rates tended to be slightly underestimated. Overall, the predictions for daily soil evaporation were also accurate. Model estimation errors were probably due to the simplified modelling of soil water content, stomatal resistances and soil heat flux as well as due to the uncertainties in characterising the 2 micrometeorological conditions. The SW’s prediction of transpiration was most sensitive to parameters most directly related to the canopy characteristics such as the partitioning of captured solar radiation, canopy resistance, and bulk boundary layer resistance