Potassium Fertilizer and Nitrogen Use Efficiency

When managing soil nutrient sufficiency ranges, most are attempting to keep each nutrient above the critical and within the adequate range.  This, of course, depends on the soil, region, crops being grown etc.  Sufficiency ranges have been developed over time through field calibration research, linking crop yield/response to soil test levels.  From these crop responses, different soil test ranges have been made insufficient, sufficient or excessive.  This has been the standard to determine a crop’s overall needs, but what has been studied further is the relationships between different nutrients.

There are many cause and effect relationships between soil nutrients.  Too much calcium, for example, can affect the phosphorus availability in certain soils.  Soil pH is the determining factor for nutrient availability etc.  A connection between potassium and nitrogen is not often discussed, and perhaps because there is present-day data supporting this.  Unlike calcium and phosphorus availability, potassium and nitrogen are more about aiding uptake.

Potassium (K) improves nitrogen use efficiency in a few ways.  The first is potassium contributes to root elongation.  Better root growth promotes contact with nitrates and ammonium in the soil for plant uptake.  Nitrogen is primarily brought into the plant through a process called mass flow.  Mass flow is regulated by plant transpiration. This is the movement of dissolved nutrients.  As the plant transpires, more soil solution is being brought into the plant through the root system.  Transpiration can have a large effect on nutrient uptake.  It requires soil moisture to regulate plant temperature, and water/nutrient transport.  Temperature, humidity, light and wind all play a part in the rate of transpiration.

Potassium is the primary ion controlling transpiration and plant nitrogen mobility.  Low K can cause nitrogen to accumulate in older tissues instead of moving to newer growth.  It controls the stomata movement on the leaf surface.  Stomata are the pores regulating water and gas exchange.  When stomata open, potassium ions move into the guard cells and vice versa when they close.  Without proper plant K levels, which can be greatly affected by soil moisture and clay type, the mass flow of nutrients such as nitrogen are inhibited. 

The fact is that growing organisms have a balance amongst themselves.  Yes, insufficient nutrient content can raise a plant but keeping them in a constant balance is what increases the efficiency of others for maximum yield potential.  Constantly maintaining a sufficient range of nutrients is the first step and the next is to learn the cause and effect of nutrient levels.