The most important factors influencing crop yields are the amount of water available and the amount of sunlight. While we have no real influence on the latter factor, proper water management is possible and necessary. Agriculture uses about 70% of the water used in the human economy worldwide.
In Poland, it is much less, as the largest consumer of water is coal-burning energy. According to Organisation for Economic Co-operation and Development (OECD) experts, as much as 80% of crops, which provide 60% of global food production, is agriculture using only water from rainfall. Ideal water conditions for plants are those in which precipitation covers evaporation losses from the soil, from plants and from surface and ground runoff. Under conditions of periodic precipitation deficiency, the key element for good plant health is the soil, which is the natural water store for plants. The greater the water holding capacity of the soil and the ability of the deeper layers to be undersaturated, the better the water supply for plants during drought periods. Insufficient precipitation, especially with higher temperatures and increased evaporation, poses the greatest problems for agriculture, as we have seen in Poland for many years. It is estimated that more than 700 million people in 43 countries currently suffer from water scarcity. By 2025, 1.8 billion people will live in countries or regions with dramatic water scarcity, and two-thirds of the world’s population could be living in permanent water scarcity. For areas that have sufficient heat resources but periodic water shortages – which includes desert areas – the alternative to precipitation is irrigation. From an economic point of view, irrigation is a very important factor for increasing yield levels also in areas with only minor or only periodic rainfall deficits, in production directions with high unit value, such as vegetable growing, horticulture or other high-intensity crops with special requirements. The world’s agriculture applies irrigation to 20 per cent of its crop area, producing as much as 40 per cent of its food by weight.
Climate change associated with its warming is threatening both rain-fed agriculture and irrigation agriculture.
A threat to agriculture using water from precipitation alone is both changes in the amount of precipitation, its nature and its distribution throughout the year. It is projected that under conditions of progressive warming, longer periods without rainfall will be more frequent and the occurrence of precipitation will be more rapid. Under the climate conditions we already face, extreme events such as violent storms and floods will be more frequent. Large amounts of precipitation in a short period of time lead to rapid run-off of water that is not stored in the soil; moreover, they have an eroding effect on the soil, lifting soil particles in an uncontrolled manner along with nutrients, dissolved artificial and organic fertilisers and applied plant protection products. Rapid water run-off leads to flooding, inundation and floods destroying agricultural crops. Both the crops, the soil and the environment therefore suffer.
A serious problem for irrigation agriculture is the negative consequences of more intense and longer droughts, which, in addition to the above-mentioned risks associated with extreme phenomena, result in a lowering of the groundwater table. This already has a limiting effect on the availability of irrigation water in some regions of Poland.
By 2050, it is estimated that extreme weather will be responsible for the destruction of 17% of crop yields in field production.
Among the main principles of sustainable agriculture, rational water management has a central position. Water – contrary to previous views – is not an inexhaustible resource and its availability is currently changing for the worse. Irrational use of it can lead to depletion of surface and underground resources and consequently to a lack of water availability for irrigation. For agriculture, droughts are particularly severe, especially those occurring during periods of intensive crop growth. The negative impact of droughts is exacerbated by the fact of little or no snow in winters, resulting in very low post-winter soil retention at the start of the season and little spring water storage. Agriculture must comprehensively adapt to the new climate regime. This adaptation should – in addition to plant selection, optimisation of soil cultivation methods, maximisation of soil water retention – be based on rationalisation of water use and good planning of water consumption during the growing season. It is becoming necessary to take into account the time-varying water requirements of individual crops and their varieties, linked to the characteristics of the climate and the soil on which they are grown. Proper zoning of irrigation and assessment of the abundance of available water sources is crucial. While this assessment is relatively easy in the case of surface water, the abundance of groundwater sources is much more difficult to assess and should be carried out by specialised operators. Ideally, the farm should be equipped with automatic, or manual, monitoring of groundwater levels. It is becoming very important – in view of projected climate change – to minimise the risk of pollution of watercourses, reservoirs and other water resources.