Deficit irrigation

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Under deficit irrigation refers to the agricultural irrigation with a deliberately below the optimum water requirements of the crop is water added. At the same time, it is a question of ways of increasing water efficiency in agriculture.

Principle and Mechanism

Deficit irrigation aims to create targeted drought stress in the crops in those phases that have hardly any effect on the crop yield. Ultimately, a small reduction in yield with high water savings is accepted. The focus of the strategy is on stabilizing or optimizing agricultural yields while maximizing water productivity (i.e. increasing economic income in relation to water abstraction from nature).

The following physiological connection can be used for this purpose: Most of the water given off by plants is returned to the earth's atmosphere via the transpiration of leaves . The amount of water released from the leaves is controlled by the opening of the stomata , which in addition to the release of water also regulate the uptake of carbon dioxide , which is important for photosynthesis as well as for the structure of matter. One of the essential scientific findings on which deficit irrigation is based is that the regulatory mechanisms of the stomata and thus the plant metabolism can be consciously controlled through different watering.

Based on these considerations, irrigation strategies have been developed in the last decade that lead to similar yields with lower water volumes and thus significantly improve water use efficiency. These strategies sometimes even lead to better plant health and have a beneficial effect on the quality of the products produced .

Different approaches to deficit irrigation

A distinction is now made between different strategies of deficit irrigation, which are initially used primarily in fruit growing and viticulture internationally:

  • regulated deficit irrigation (RDI)
  • partial drying of the root zone (PRD, partial rootzone drying)
  • sustainable or sustained deficit irrigation (SDI)

Regulated deficit irrigation

With many types of fruit , but also with some grains , the size of the fruit affects its content of ingredients. In the case of red wine grapes , for example, the size of the berries has a significant impact on the tannin and aromatic content of the wine. In addition, small berries produce a lower proportion of juice in relation to the coloring, tanning and flavoring substances contained in the berry skin.

In addition, a slight drought stress at the beginning of the ripening phase of the grapes is important for high quality red wines. The best wine quality always came from vines whose grapes had small berries.

In viticulture, therefore, the following rule can be established: Avoid optimally supplying the grapes during the fruit set phase , as otherwise the berries will be too big in autumn. In order to keep the berries small, the water supply to the vineyards is specifically reduced to a minimum from the flowering period until shortly before the start of ripening. Before the color change, the water is then watered more intensively again, in order to then insert a second drying phase at the beginning of ripening (immediately after the color change); From the middle of the ripening phase, more water is then used again. The drought stress generated in this way promotes the formation of abscisic acid in the plants .

With conscious handling, the growth of the shoot comes to a standstill through the "regulated deficit irrigation"; at the same time, the berries stay smaller and contain more ingredients and also have lower pH values . However, lower yields can be expected with this method.

Partial drying out of the root zone

This strategy of deficit irrigation is based on the fact that, for example, the roots of vines in a soil that is slowly drying out produce chemical messengers such as abscisic acid, which are passed on to the above-ground parts of the vines. This signals to the above-ground parts of the vine that the water supply to the plant is becoming scarcer. The leaves then reduce transpiration and thus water consumption by closing the stomata. This also reduces the gas exchange ; the assimilation performance of the plant decreases and further leaf and shoot growth slows down or, in extreme cases, comes to a standstill. In this situation the plant prefers to feed the grapes. As long as part of the roots of the vine can still supply enough water to maintain the vital functions of the plant, consequently no drought damage occurs, even if the vegetative growth is reduced overall.

If the soil is very dry, the abscisic acid production of the roots in the dry soil areas comes to a standstill. However, the root tips in the dried out soil do not die off, but remain in an inactive state. The vine does not consume water during the night; all parts of the plant, including the roots in dry soil, are supplied with water during this time. In this way, the roots can survive long periods of time in the dried-out area, provided that some of the roots of the vine still supply enough water. If the dry soil is moistened again, the roots in it become active again and can take over their tasks again; photosynthesis can now also achieve full performance again and thus start sprout growth.

Not only in experiments but also in practical tests in viticulture has shown that this irrigation strategy changes both the grape and the wine quality in a beneficial way. Compared to traditional drip irrigation , the amount of irrigation can be roughly halved without changing the amount of yield.

Persistent deficit irrigation

The sustained deficit irrigation (SDI) differs significantly from the two previously described irrigation strategies . Here less and less water is given in the course of the irrigation period; at the same time, the water available in the soil continues to decrease over the course of the vegetation period. This slowly increases the water stress for the plants and they can adapt to it. This strategy is more suitable for wheat , sunflower or corn than for millet or cotton because of the yield development . The cultivation of adapted varieties also makes more sense than that of high-yielding varieties .

implementation

In recent years, the agricultural management of water demand has been increasingly viewed as an important instrument for achieving a balance between demand, supply and optimized use of water. Applying deficit irrigation can reduce agricultural water consumption per unit of land. This can either counter the expected scarcity of water in numerous irrigated regions of the world or expand the irrigated area. According to the models and operating experience available so far, the gross profit margin for farmers will be greater for deficit irrigation than for full irrigation.

literature

  • Marshall English, Syed Navaid Rajy (1996): Perspectives on Deficit Irrigation Agricultural Water Management 32: 1-14.
  • Iván Francisco García-Tejero, Víctor Hugo Durán-Zuazo, José Luis Muriel-Fernández Water and Sustainable Agriculture Springer: Heidelberg etc. 2011, especially chap. 5.1.
  • Martin Stoll (2005): Watering specifically - stressing consciously. German Viticulture 9: 24-25.

Web links

Individual evidence

  1. a b Cf. Barbara Raifer / Günther Pertoll Irrigation strategies in viticulture
  2. Elias Fereres, María Auxiliadora Soriano Deficit irrigation for reducing agricultural water use in: Journal of Experimental Botany 58 (2006), pp. 147-159
  3. cf. 2030 Water Resources Group (Ed.). Charting Our Water Future. 2009 ( Memento of the original from April 17, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 5.8 MB) and Thomas Kluge / Engelbert Schramm target horizon 2050: Integrated system solutions as a sustainable innovation strategy for companies in the water sector. In: Korrespondenz Abwasser 8/2013: 691–698 @1@ 2Template: Webachiv / IABot / www.2030waterresourcesgroup.com
  4. Optimization of water consumption in agriculture through deficit irrigation ( memento of the original from February 26, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.energyglobe.at