Crop yield response to water - Cra

ecommended fertilization rates range from 100 to 250 kg/ha N, 50 to 100 kg/ha P 2 O 5 ,and 60 to 260 kg/ha K 2 O, for soils ranging from highly fertile to highly deficient in thespecific nutrient.The crop is moderately sensitive to soil salinity with a threshold of the electrical conductivityof the saturated soil paste extract (EC e ) of 2-3 dS/m, reaching 100 percent yield loss at 10 dS/m.Irrigation practiceMost common irrigation methods for potato are furrow and sprinkler. Yield response tofrequent irrigation is considerable and very high yields are obtained with the mechanizedsprinkler systems where evapotranspiration losses are replenished each or every two days.Frequent and timely irrigation reduces the proportion of malformed tubers at harvest. Whererainfall is low and water supply is restricted, irrigation scheduling should be aimed at avoidingwater deficits during the stage of stolon formation, tuber initiation and after tuber initiation.Supply of water can be restricted during the early growth, i.e. before flowering, but canopygrowth would be slowed so the restriction must be within bounds. To use up more of thewater stored in the soil, irrigation should be cut back toward or at the senescence stage. Thispractice may also hasten maturity and increase dry matter content of tubers. Correct timing ofirrigation may save 1 to 4 irrigation applications, including the last irrigation prior to harvest,depending on the situation.YieldIn the temperate region of northern Europe and North America, a good yield, under irrigationwhere required, is more than 40-50 tonne of fresh tubers per ha. In very humid regions, yieldtends to be less as diseases are more difficult to control. Yields of rainfed and even irrigatedpotato in the subtropics and cool tropics are much lower, ranging from 5 to 25 tonne per ha.Planting low quality seed tubers, less dense planting, lower rates of fertilizer and irrigation,and pest and disease problems led to the low yields. Seed tuber quality is very important forhigh production, as reflected in the large amount of seed tuber in world trade, amounting toabout 1.4 million tonne per year. Dry matter content of fresh tubers normally varies between20-25 percent of fresh weight.Economic yield depends strongly on tuber quality, and can be affected by irrigationmanagement. Water deficit in the early part of the tuberization stage increases the occurrenceof spindled tubers, which is more noticeable in cultivars of cylindrical tuber compared to thoseof round tuber. Water deficit during this stage followed by irrigation may result in tubercracking or tubers with black heart. Water deficit following tuber initiation can reduce theyield of marketable tubers from 90 percent to 70 percent or even 50 percent.188crop yield response to water