NISKU, Alta. – The availability of some crop-accessible soil nutrients improves the longer a field is in zero till, said Rigas Karamanos, agronomy manager for Westco. He said a farmer who is aware of these improvements can use them for economic benefit. Ignoring those changes is to waste input dollars.
The most important of these changes is due to the added residue on the soil surface and lessening of soil disturbance beneath that residue, Karamanos said at a recent direct seeding conference held in Nisku.
When producers talk fertilizer efficiency, nitrogen always tops the list because of the escalating cost. Mineralizable nitrogen is significantly increased in zero till, said Karamanos. Mineralization is the conversion of organic nitrogen to inorganic nitrogen through microbial decomposition of soil organic matter, which makes it more available to the plant.
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Karamanos said the improvement in nitrogen quality under reduced or no-till systems is reflected in greater gains of fertilizer-derived nitrogen in the organic part of the soil. See chart on recovery of fertilizer N and Nitrogen derived from fertilizer.
But it’s not all a bowl of cherries. Different kinds of soil chemistry changes can take place under no-till. While mineralizable nitrogen in the soil increases, actual mineralization may not be affected or may even decrease.
Immobilization can also increase, converting inorganic nitrogen to organic nitrogen, which is unavailable for plant use.
Nitrate accumulation results in residual nitrate in the soil. This is the nitrogen measured in fall or spring soil tests, upon which fertilizer recommendations are based.
Some research has shown that residual nitrogen under minimum disturbance tends to be lower because of lower net mineralization or higher denitrification.
Although levels of available phosphorus are not affected by tillage, both mineralization and plant-available phosphorus are higher under reduced tillage systems. The increased phosphorus availability under minimal disturbance has been linked to greater colonization of mycorrhizal fungi that live with certain plant species.
While there appears to be no difference between no-till and conventional-till when it comes to measuring phosphorus at the 15 centimetre depth, it appears that phosphorus tends to accumulate in the top five cm in a no-till system.
Potassium levels are generally increased under zero tillage, but the same stratification issues that affect phosphorous also affect potassium.
Under zero till, the changes in crop-relevant sulfur are small and have minimum impact on the overall crop fertility.
In general, said Karamanos, reduced soil disturbance creates higher microbial biomass, higher enzyme activity, greater aggregate size and stability, better water infiltration and holding capacity plus additional large pores in the soil.
The overall improved soil quality influences the supply and absorption of nutrients required by the crop.
