Crop yield response to water - Cra

techniques; d) relations between yield and water use; and e) water management strategiessuggested under limited water supply.World trends in fruit tree and vine productionThe rapid rate of world economic development in recent decades has been accompanied bymany transformations; an important one is the change in human diet, such as the increase indemand for animal products in many emerging economies. In most countries, health-relatedconcerns have led to a renewed interest and increased consumption of fruit and vegetables.Strong consumer demand has resulted in the production of high-quality horticultural products;a very high priority of both public and private institutions worldwide. This increased demandfor fruit is expected to continue and presents an incentive for growers to develop efficienthorticultural industries, which in most areas will be dependent on irrigation.Current water demands by other sectors of society require that the agricultural sector reduceswater use for irrigation; the world primary user of diverted (developed) water. Indeed, currentagricultural water use is considered by some competing interests simply another ‘source’ of water,since the development of additional water supplies has been limited, especially in developedcountries. In many parts of the world, one result of reduced water supply for agriculture hasbeen a shift in cropping patterns to economically more viable crops; from annual field crops tohorticultural crops, such as fruit trees and vegetables. Figure 1 shows that the areas devoted togrowing fruit and vines in a number of countries have increased significantly over the last 20years, indicating that this is a general trend in irrigated agriculture in most parts of the world.Recent improvement of irrigation and management methods have reduced irrigation-relatedwater losses, thus decreasing the amount of applied water per unit of irrigated land. Both theshifts towards high-value crops and towards higher application efficiency suggest that morewater should be available for irrigation of trees and vines. However, these improvements havecoincided with an expansion of irrigated land, to the extent that most of the water saved hasgenerally been used to irrigate additional land or crops that have higher water requirements.In many cases, the water requirements of tree crops exceed those of the major field crops thatwere previously grown in these areas. Therefore, the availability of water for tree and vineirrigation most likely will continue to decline. This will be more so in areas where the supplieshave been stretched to the limit and where environmental water needs are considered highpriority by society and are in direct competition with irrigation needs.Towards intensification in fruit and vine productionThe general trend in fruit-tree production over the last decades, as in other forms ofagriculture, has been towards intensification. This trend is manifested as an increase intree or vine density, often coupled with the use of dwarfing rootstocks to reduce treevigour. There are many reasons for the success of these intensive plantations, relative tothose that are traditional low density. Greater radiation interception results in increasedcarbon assimilation and productivity and lower vigour reduces pruning needs and oftenharvesting costs; both of which are significant expenses in orchard production. Since accessto the orchard is improved because the drive rows (areas between the tree rows) are notusually wetted by microirrigation, pest control applications are easier and on time. In short,high-intensity orchards are more manageable. Their major limitation is the higher capitalYield Response to Water of Fruit Trees and Vines 247