Effects of different irrigation regimes on the growth and yield of drip-irrigated potato

Potato (Solanum tuberosum L.) is a relatively sensitive plant to water stress and is widely planted in Japan. Soil water is one of most important factors affecting the yield and quality of potatoes. Under a rainshelter, an experiment was conducted to evaluate the effects of different amounts of drip irrigation water on the potato growth, tuber yield, size and specific gravity. The amount of irrigation water applied was 0.25, 0.50, 0.75, 1.00 and 1.25 times of water surface evaporation (Ep) measured by a standard 0.2 m diameter pan (K=0.25, 0.50, 0.75, 1.00 and 1.25). Plant height, biomass and shoot water content increased, but the specific leaf weight (SLW, g/m^2) decreased with increasing amount of irrigation water. The amount of irrigation water had significant effects on decreasing the canopy temperature. Total fresh tuber yields and marketable tuber yields (>85 g) increased with increasing amount of irrigation water. The highest yield was obtained at the 1.25 times regime and the total tuber yield was close to the theoretical maximum. Irrigated water increased yields not only by increasing tuber number, but also by increasing the mean weight of the tubers. Irrigated water increased potato tuber quantity, but decreased potato tuber quality. The specific gravity of potato tubers tended to decrease as water applied increased, and the scarred and the hollow-heart potato tubers increased with increasing amount of irrigation water. So, under controlled environmental conditions, potatoes should be irrigated using pan evaporation factor more than 0.75 (K>0.75) that is a guideline. The use of lower pan factor (K<0.75) may reduce potato tuber yield significantly.