Planting into Dry Soil

By James Hoorman, Hoorman Soil Health Services

Grain harvest has started but many areas have low soil moisture.  Planting grains or a cover crops into dry soil can be difficult.  The crop may germinate but may not grow or survive if adequate moisture is hard to obtain.  Here are some planting considerations if your soil is dry and you are trying to plant another crop.

First, the goal is to conserve moisture. No-till grains like wheat or rye or even other cover crops will help conserve moisture.  Tilled soils lose about .5-1.0 inch of soil water. Most wheat and cover crops need at least 35%-45% soil moisture to germinate.  A worst-case scenario is if just enough moisture causes seed to germinate, but then not enough to keep it alive.  If your soil is really dry, either plant before a good rain or right after one. If planting deep, a hard rain may cause the soil to crust.  This would be less of an issue in no-till fields than fields that are excessively worked, where the soil is fine, which tends to crust more.

Second, for wheat, plant a little deeper, at least 1 – 1.5 inches deep.  Also increase the seeding rate if planting later and into dry soils.  For wheat, a normal seeding rate for red winter wheat is 1.2 to 1.6 million seeds per acre.  In dry conditions and if planting late, by more than 2 weeks past the Hessian fly free date, increase the seeding rate to 1.6 to 2.0 seeds per acre.  Most wheat is planted or drilled in narrow rows (7.5 inches) which is even more critical in a dry year or when wheat has been planted late. The ideal temperature for wheat planting is 54 to 770F which is not a problem this year.  

Third, avoid planting nitrogen (N) or potassium (K) in the row furrow.  Wheat needs very little N in the fall.  Both N & K are salts which may reduce germination if they are too close to the seed.  Salts tend to draw moisture away from the seed, making seed germination more difficult.  Adding some phosphorus (P) can be beneficial in getting wheat or cover crop seed to germinate and grow faster in the fall. 

Fourth, some bioactive gibberellins promote germination.  Some seeds companies now use gibberellins to promote seed germination.  Gibberellins are auxins or hormone which are a type of fulvic acid that may stimulate seeds to grow faster, including germination.

Fifth, for cover crops, broadcasting seed should be avoided if soil moisture is lacking. A light rain may allow the seed to germinate, but it the seed can die without adequate follow-up moisture.  Most seed that lays on the soil surface will simply wait for adequate moisture to occur. This can delay germination and the seed may not survive the winter.  For cereal rye, this is not an issue as it can germinate  320F  and come up under the snow.  However, seed laying on the soil surface is subject to blow or wash away, be eaten by voles (field mice), slugs, hungry earthworms, or birds. Getting small seed in contact with soil increases the rate of cover crop survival and success. 

Sixth, for cover crops, review your past year herbicide program.  Many herbicides will carryover and have a longer half life when soil conditions are dry.  This may reduce cover crop seeding success.  They may germinate, but the stand can be thin or non-existent by spring.  Often plants that survive are weak and grow slowly.  Herbicide carryover is a major problem with cover crops in a dry year. Try a bioassay by planting some cover seed in a dish with your soil to see how seeds germinate and grow before planting if herbicide carryover is suspected.  

A big issue this year, may be subsoil moisture.  In some places, the soil is extremely dry deep in the soil.  Wheat and cover crop roots can grow down to 14-30 inches deep. In tiled fields, if the tile is not to grade, all roots (wheat, hay, grasses, cover crops) will seek out moisture in the old clay or newer plastic tile.  If roots find standing water in these tile, they can clog them up. Keeping tile to grade or avoiding any nutrients like manure or barn runoff can prevent roots from clogging tile lines.  A constant source of water like springs in a tile line has also been shown to increase root clogging in a dry year.

Every year has it challenges. However, planning ahead and being prepared for the worst-case scenario can reduce some problems. Next year, it moisture is still limited, be prepared to terminate cover crops early to conserve moisture.   

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