What About the Water?

Water... handle with care

Of course farmers use a lot of water... they are shipping water (in the form of food) to you

 Agriculture is the largest user of fresh water in the world and as demand grows for more food production, conflicts regarding water use are inevitable. In some areas, additional investment in irrigation and water supplies may provide room for further expansion of irrigated cropland. However in most areas of western North America, water is no longer in abundant supply and ferocious arguments erupt over water allocation. Since new supplies of irrigation water appear unlikely, there is significant incentive to improve water use efficiency. The pressure on the agricultural industry to carefully conserve water resources will certainly intensify. 

Soil water during the drying process

Water uptake and plant nutrient absorption are closely related. When plant roots take up water, dissolved nutrients are carried to the root surface. When water uptake is restricted, the delivery of nutrients to the root also slows down. As the soil dries and the films of water between the particles shrink, the processes of mass flow and diffusion that bathe the roots with nutrients eventually come to a halt.

An impaired root system hinders water and nutrient uptake

Healthy roots and water use

An important step towards improving water use efficiency is to encourage healthy plant roots. Maintaining proper soil conditions will enhance the volume of soil that roots explore. For example, a soil that has a compacted zone or a hard pan will present a barrier to plant roots and restrict their use of moisture deeper in the soil profile. Similarly, when subsoil acidity is not addressed, plant growth is stunted and roots cannot grow deep into the soil to utilize water and nutrients.

Plants grown with adequate nutrition typically have larg­er tops and root systems compared with crops grown with an inadequate nutrient supply. These well-fertilized plants are generally larger and may have greater water loss (tran­spiration), but a lower transpiration ratio. In other words, the healthy plant may use more water, but will generally produce larger yields. This translates into more yield per gallon of water extracted from the soil. Another way to say this is that greater water use efficiency results from proper plant nutrition. 

How much water is in our food?

It seems like there is rarely enough water in western North America to meet everybody’s needs. Especially after several years of prolonged drought in many areas, farmers are stressed to learn that there may be insufficient water to grow their crops.

The amount of water required to grow a crop

A common cry from the urban areas is that agriculture uses more than its “fair share” of water. Some estimates have been made that more than 80% of developed water is go­ing to agriculture in many areas. Attention is drawn to the fact that agriculture loses too much water through cracks, seepage, and evaporation from the miles of canals and pipelines. These losses should be addressed when financing is available. 

Most consumers do not appreciate the large amount of water required to grow plants. A poorly understood concept is that a huge amount of water is indirectly delivered to cities in the form of food. A report by the Water Education Foundation documented the amount of water required to produce various foods in the western U.S. Their basic ap­proach was to divide average water use (evapotranspiration) by average yields to determine the gallons of water per pound of food produced. Since some of the water delivered to a farm is unavoidably lost as deep percolation, runoff, or soil moisture storage, the irrigation efficiency was assumed to be 70%. 

Using a typical 2,300-calorie menu proposed by the U.S. Department of Agriculture, the following meal was con­structed and the gallons of water required to produce that particular food item are shown.

The amount of water required to grow our daily food

Do farmers use a lot of water?
Yes… and we all benefit tremendously from their produc­tivity. The water may not only come from our faucets, but it also comes to us in every bite we take.

Proper plant nutrition is a vital key to achieving efficient use of water. Nitrogen deficiencies have an impact on the ability of a crop to convert available water into yield. Phos­phorus is important in stimulating seedling root develop­ment. This helps the plant explore more soil, increasing the recovery of nutrients and water. Potassium is often referred to as the regulator nutrient, influencing the water dynamics in plants. Nutrients play an essential role in allowing plants to convert water and sunshine into food.

For a pdf version of this post, go to: 

http://www.ipni.net/ipniweb/insights.nsf/$webcontents/DA8415D5BCDB35B985257A75006FE02A/$file/MIkkelsen_Drought_Insights_2012_final.pdf