The Application Of APSIM Model And The Measurement Of Soil Evaporation Parameters In The Qingyang Loess Plateau, Gansu

To understand soil water dynamic and soil evaporation under stubble retention and to improve soil evaporation parameters for application of APSIM (Agricultural Production Systems Simulator) on the Loess Plateau, two field measurements were conducted at Xifeng, Gansu in 2006.(1): After winter wheat harvesting, five treatments were set up: fallow (f); conventional tillage (t); standing stubble retention (ss); stubble mulching (ls) and conventional tillage with stubble retention (ts). After rainfall event, a continual soil water measurement for the top 0-15 cm and 0-30 cm was observed. The results showed that soil water under two tillage treatment whatever with stubble retention or not was low. After 69.6 mm heavy rain, the runoff in t and ts treatments is significantly greater than other three treatments due to crust in the surface, as a result, soil water was significantly lower than the other three treatments. Fallow treatment reached the highest soil water content with 31.5% among five treatments, together with significant soil water content lost (over 10.19%). Both stubble retention treatments without tillage had better capacity on maintaining soil water, after 8 days, the reduction of soil water content for ss and ls treatments was 7.88% and 7.66%, which equaled to store 3.8 mm and 3.6 mm more soil water than the f treatment.(2): Before winter wheat sowing, a rainfall simulator was used to compare the soil water evaporation under different coverage. The parameter U is 7.8 and the CONA is 6.2 in fallows soil, (U represents the amount of cumulative evaporation before soil supply decrease below atmospheric demand, and the CONA specifies the change in cumulative second stage evaporation against the square root of time). Stronger evaporation rate was observed under fallow (FL) treatment, followed by 50% of stubble retention (SS), and 90% of coverage (LS) had the lowest daily evaporation during the experiment period. The cumulative evaporation amount under F treatment was 1838 g, which meant 39% and 97% more than that under SS and the LS treatments, respectively. Evaporation decreased with the increasing of amount of stubble covered on the soil surface, and the longer the stubble remained, the more evaporation was restrained.(3): Base on the experimental data, APSIM soil evaporation parameter U and the CONA were modified to 7.8 and 6.2. The correlation coefficient between APSIM predicted value and the measured value for FL, SS, LS, was increased from 0.41, 0.68, 0.59 to 0.87, 0.89, and 0.92, respectively. The fitness preformed well.By using the modified parameter U and the CONA to simulate soil water content dynamic. For experiment 1, the correlation coefficient for f, ts, t and ss treatments was 0.92,0.98,0.97 and 0.94, respectively. For experiment 2, all three treatments (FL, SS and LS) a higher correlation coefficient of 0.99 between predicted value and measured value was obtained. Results indicated that the modified evaporation parameters for primarily application APSIM in Qingyang Loess Plateau, China has perspective potential.APSIM simulated the wheat growth from 2001 to 2005 in a maize-wheat-soybean rotation system; the predicted yields were always lower than that measured data. The total biomass and grain yield performed closest fitness in drought year, , Model sensitively captured the heavy rainfall effect on whet growth at 2004. Following up study for wheat module will be required to improve the performance of APSIM in the Qingyang Loess Plateau, China.