Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2003
Publication Date: 1/1/2004
Citation: Amer, K.H., Hatfield, J.L. 2004. Canopy resistance as affected by soil and weather factors in potato irrigation scheduling. Agronomy Journal. 96(4):978-985. Interpretive Summary: Management of irrigation water in agricultural crops is a difficult task because the current methods rely on measurement of crop water status or soil water content. These methods are laborious and don't always predict the response of the crop to soil water deficits. Observations in crops like potato have shown that direct measurements of crop water status don't always provide sufficient warning of water needs for effective irrigation scheduling. An experiment was conducted over two growing seasons in northern Egypt to evaluate the use of canopy resistance as a method for irrigation scheduling. It was found that canopy resistance was sensitive to changes in soil water availability and provided a reliable method for detecting changes in soil water status that could be effectively used to manage irrigation supplies. An additional study was conducted to determine if soil salinity would confound the problem in using this method and the effect of soil salinity could be addressed in this method and not lose any accuracy. This type of approach for irrigation management for potatoes would increase the efficiency of water use and lead to better crop quality. These results will be able to assist potato growers to improve their irrigation management practices and reduce water use while maintaining or increasing crop yield and potato quality.
Technical Abstract: Irrigation requires a method of quantifying the crop water status or root zone depletion of water. A direct measure of canopy resistance has the potential of being used as a crop water status indicator for irrigation management. A study was conducted on potato (Solanum tuberosum) grown in northern Egypt at Shibin El-Kom on a alluvial loamy soil for winter (Sept. 20, 2001-Jan. 20, 2002) and spring (Feb. 1-May 20, 2002) seasons. Plant height and leaf area index (LAI) were measured weekly from emergence to maturity. Air, soil, and canopy temperatures, relative humidity, wind speed, net radiation, heat flux and soil water content were recorded as averages every 30 min throughout both seasons. Diurnal canopy resistance was determined for well-watered conditions and achieved minimum value of 20 and 10 s m-**1 at noontime during winter and spring periods, respectively. A power relationship for well-watered conditions was developed between canopy resistance and net radiation at various plant growth stages. The power was around - 0.86 for all growth stages but the equation constantly differed based on LAI for early growth and mature stages. In deficit soil water conditions, canopy resistance increased linearly with decreasing available soil water with a change in potato canopy resistance of 0.75 and 0.387 s m-**1 / % available soil water for 1 and 2 MJ m-**2 h-**1 of net radiation at mid-growth, respectively. A ratio of actual/potential canopy resistance was derived to normalize the meteorological differences between growing seasons. This ratio was 2.5 when 50% of available soil water was removed and can be used as a parameter to automatically schedule irrigations using weather factors and canopy temperature. Canopy resistance increased linearly with increasing soil solution salinity, electrical conductivity (EC), when the soil solution was above the threshold soil salinity value. A ratio of rc/rcp was found in use for potato irrigation scheduling for both saline and water deficit conditions. Canopy resistance can be used as a method to schedule irrigations in potato.