Potassium nitrate: a key ally in combating water stress

It is undeniable. Climate change is already affecting agriculture in the United States. In California, Florida and the American Midwest, regions I travel frequently, water shortages or drought are seriously limiting agricultural production. The effects are most evident not only in irrigated crops, such as almonds, but also in rainfed crops including wheat and corn, among many others.

Effect of mean solution K concentration on plant DW, leaf K concentration and WUE.

When the K concentration in the sunflower nutrient solution was increased from 0.1 mM K to 2.5 mM K, then dry weight (DW) also increased, leaves showed higher K concentrations and WUE was higher (Fournier et al, 2005).

The main problem is water stress, the dreaded phenomenon that inhibits photosynthesis and photochemical activities of plants. This phenomenon affects plant enzymatic activities, which has a serious negative impact on crop quality and yield.

Yield loss due to abiotic stress (a category that includes water stress) is estimated to be staggering: 65.8% for corn, 82.1% for wheat, 69.3% for soybeans and 54.1% for potatoes.Needless to say, state-level actions are required to address the problem. But farmers themselves have the power to increase the water use efficiency of their crops by choosing the right nutrients for it.

Some nutrients, such as potassium and nitrate, have already been shown to significantly increase water use efficiency in plants. These types of nutrients are a strategic ally on sites where water supply is restricted. And in areas where there is an adequate water supply, the use of potassium and nitrate will increase yields per acre, or alternatively, allow any excess water to be used to irrigate additional crops.

Potassium nitrate (_KNO3) is a fertilizer that contains a readily available source of two macronutrients that play a very important role in increasing water use efficiency (WUE). Both nitrate (_NO3) and potassium (K) are highly soluble and can be readily absorbed by plants.

The synergy between potassium and nitrate in the soil promotes the rapid uptake of both ions by plant roots. The dominant effect of the presence of N (as _NO3), a negative ion, stimulates the uptake of positively charged ions in the soil. In turn, potassium stimulates the uptake of _NO3 and promotes root growth. This vital combination has been shown to work very efficiently. Plants that are under water stress and suffer from potassium deficiency sweat more and therefore need to absorb more water to stay healthy.

Research shows that wheat crops with adequate K supply manifested higher WUE when they received nitrate compared to ammonium as a nitrogen source. Thus, potassium nitrate is essential for efficient water use.

Water use efficiency (WUE) (g / L of water)

Figure 2. WUE of wheat was higher when plants were fed nitrate compared to ammonium as a nitrogen source when grown under three different concentrations of K in the nutrient solution (Lips et al, 1990).

Some studies have concluded that corn treated with higher amounts of potassium is better adapted to water stress, and that an adequate potassium supply is essential to increase drought resistance. Potassium is credited with the increased stability of the cell membrane to adjust its osmotic capacity. Potassium also plays a role in controlling stomatal opening to help regulate transpiration. Therefore, an adequate supply of potassium is essential to increase drought resistance by increasing water uptake through the roots and controlling water loss through the leaves. Better water uptake also means better nutrient uptake contributing to yield.

In times of climate change, water scarcity can result in a huge cost for agricultural production. Therefore, it is very important to consider the use of potassium nitrate when rationalizing water use and optimizing water resources. By considering all these factors, we will be able to achieve improved yields, even under adverse conditions.

Figure 3. K intensifies the transport and storage of assimilates from leaf to fruit.

BY JW LEMONS National Sales Agronomist SQM North America - Published in CropLife magazine, April 2019.