جستجوی مقالات مرتبط با کلیدواژه "پنمن مانتیت" در نشریات گروه "آب و خاک"

Plant yield is a function of root distribution and its activity. Under limited water conditions, adequate root growth and efficiency are essential for crop productivity. To study the relationship between the dynamics of corn (Zea Maize L., variety single cross 704) root growth and soil available water uptake under drip-tape irrigation system, an experiment was conducted in a randomized complete block design with three replications. Experimental variables were three irrigation treatments including: 100% (I1), 80% (I2), and 60% (I3) of the actual plant water requirement calculated by the Penman–Monteith formula using meteorological data. The roots were collected from the beginning to the end of the growing season at four stages including: 25, 55, 85 and 115 days after planting. Samples were taken from 5 depths: 0-10, 10-20, 20-30, 30-40, and 40-50 cm. The results showed that irrigation treatments had significant effect (p=0.01) on root length density at different depths. About 60% of the corn root length density was up to the depth of 20 cm. On the other hand, the surface layers of the soil at this depth lost their moisture rapidly and, therefore, the plant needed to absorb water from the lower layers (below 20 cm) to survive. In low irrigation treatment (60% water requirement) up to the depth of 40 cm, root growth was low and, as a result, water absorption was also low. Higher irrigation had a positive effect on corn yield as the highest yield (7769 kg/ha) was obtained with the irrigation treatment of 100% water requirement.

Accurate estimation of crop water requirement based on evapotranspiration calculation has an important role in improvement of field water management. The Penman-Monteith equation is the most common method for estimating reference crop potential evapotranspiration. However, this equation needs full weatherr data, but a few stations with complete weather data exist in Fars province. On the other hand, the Jensen- Haise equation is a more simple method for estimating reference crop potential evapotranspiration. In this study, using the weather data of some synoptic stations in Fars province, the Jensen- Haise equation was calibrated and then evaluated based on Penman-Monteith method for every month of the year. For this purpose, the calibrated coefficients of the Jensen- Haise equation were determined for all months and all stations, separately. Also, the monthly effective temperature (combinatio of minimum and maximum monthly temperature with a constant coefficient) was used instead of monthly mean temperature in calibration stage, and the results indicated the appropriateness of this replacement for estimating evapotranspiration. Furthermore, the estimated sunshine hours (based on minimum and maximum monthly temperature) were used instead of measured sunshine hours in validation stage in Jensen- Haise equation, and the results indicated the appropriateness of this replacement for good validation of this equation in Fars province. Finally, the results indicated that the adjusted Jensen- Haise equation was appropriate in Fars province.