Managing fertilizer’s salt effect in drought

The salt effect

When the soil starves for moisture, the salinity of the soil increases. Heat and drought cause an increase in evaporation, pulling water out of the ground and pulling the salts to the surface. This can be seen by a white crust on the soil’s surface either in small areas a few feet in size (locally), or measuring a few acres in size (regionally). 

These areas are lacking in seedbed moisture, and plants will struggle to capture water as the salt will draw the moisture away from the roots and impede the plants uptake. This can cause germination damage, wilted foliage, discolouration and stunted plant growth.

All seed-placed fertilizers, including Nitrogen (N), have salts, and will increase the salt concentration in the soil when soil moisture conditions are bad. When there’s no moisture for the seed to absorb, the fertilizer salts can cause seedling desiccating or ‘seed burn.’

Managing soil salinity

The key to managing soil salinity levels boils down to moisture. Nitrogen and other fertilizer nutrients are needed for plant growth and crop yields, so salt will always be in the soil mixture. The only way to effectively manage the salt is with water.

Having good seedbed moisture is the first step. Direct seeding or zero-till technology helps put the seed in the best position to succeed, as tilling dries the soil. Soil texture and organic matter also contribute to seedbed moisture. Sandier, Brown/Grey soils with low organic matter will tolerate less applied N than soils with higher organic matter and more clay content. Higher organic matter and clay content provides a greater holding capacity for water in soil.

Before applying N or other fertilizers, it is also important to understand the capacity of the crop being seeded. Different crop types can handle more seed row-applied fertilizer than others. Cereal crops tolerate a higher rate of fertilizer than canola, flax or other crop types. Different fertilizer types and brands will also carry different amounts of salt content. Knowing the salt content in the fertilizer can help manage soil salinity.

Another aspect to consider before applying seed-placed nutrients is to consider the Seedbed Utilization (SBU) of your seeding implement. The SBU is a function of the width of seed and fertilizer scatter behind the opener and row spacing. 

Narrow openers paired with wide row spacing create a low percentage SBU, while if both seed and fertilizer get broadcasted equally across the field, the SBU would reach 100 per cent. The SBU measures the portion of the seedbed that is actually used for seeding and fertilizing. As the SBU increases, the safe seed rate increases, as the amount of seedbed soil being used increases.

And while the soil’s pH levels are not directly related to the salt effect, it is related to the seed-safe rate. Fertilizers can increase the acidity of the soil and potentially cause germination damage if not done carefully and attentively.

All of these factors are used to adjust and determine what is considered the “safe rate” for seed placed fertilizers.

Safe rates for seed placed fertilizer

‘Safe’ rates for seed placed fertilizers are a set of guidelines for growers to use to avoid seed burn caused by fertilizers. The seed-safe rates are published for each of the three prairie provinces and provide guidelines for each crop and fertilizer type, but are more effective when specifically fitted for specific soils and conditions using the factors mentioned previously. 

These rates provide you the maximum safe application of N and other fertilizers if there were to be drought or lack of moisture, helping you avoid seedling injury. Safe seed rates can help you get an idea of how much fertilizer you should be putting in the ground, and are especially helpful during times of drought. 

For more information on implementing a soil health strategy on your farm, contact us today.