Management of Water and Salinity

Water Management 

Table grape production generally requires 400 –1350 mm (4 000 – 13 500 m3/ha) of available water per year depending upon climate, soil, variety, etc. to achieve maximum productivity. Thus, irrigation and fertigation are increasingly practiced in many countries, especially where rainfall is limiting vine growth. Irrigation is increasingly viewed as essential for quality table grape production in the hot dry climates where the crop is predominantly produced.

In some regions, e.g. desert areas of South Africa, 2000mm of irrigation water can be applied every year. Application of 600mm irrigation water is the norm in Spain. Production is largely influenced by amount of water available between flowering and veraisons, however, shortage of water at any growth stages will result in reduction of yield and quality. Soil water management is critical to produce good quality berry. When the soil is too dry, table grape yield and quality are reduced.

Lack of available water during early growth results in wilting of leaves and succulent shoots. At the first sign of drought, rapidly growing tips become more grayish green. Tendril die back and drop are useful indicators of early drought stress. Shortage of water during rapid berry enlargement restricts berry size and directly affects yield and quality.

A slight shortage of water during maturity hastens ripening of berry by limiting shoot growth in order to increases sugar content by restricting berry size, while over-irrigation and rain during ripening will delay maturity, can lead to berry split and softening, and will cause disease invasion. Longer periods of exposer to waterlogged soil is resulted in root death, restriction of growth, low yield, and poor quality of berry. Supply of sufficient amount of water resulted in increase of table grape yield.

Salinity 

More than 50% of the world’s agricultural irrigated land is affected by salinity problems. In table grapes, particularly where non-tolerant rootstocks have been planted, salinity induces a water deficit in the vine and also leads to an imbalance of nutrient uptake that resulted in deficiency of certain nutrients (e.g. calcium) or toxicity due to an excessive uptake of other ions (e.g. chloride and sodium). The end results are stunted growth, drought stress, wilting, and leaf death leading to a reduction in yield and quality.

Application of appropriate form of nutrients and balanced nutrition particularly calcium, potassium, and nitrate nitrogen can minimize salinity problems. For example: 

• Nitrate N may reduce chloride uptake and will improve potassium, calcium and magnesium uptake. 
• When Nitrate N is supplied as calcium, potassium, or magnesium nitrate it also improves water uptake compared to ammonium form of nitrogen. 
• High level of calcium in the root zone can reduce adverse effects of sodium and chloride uptake, while it increases potassium and nitrate utilization.