Nutrient management in no-till and minimum till systems
With increased acres of no-till and minimum till in Montana, it has become important to describe differences in nutrient availability and recommended fertilizer application practices between no-till, minimum till and conventional till systems. In addition, no-till practices have changed the surface layer which affects soil nutrients both at the surface and deeper in the soil profile. An understanding of nutrient availability differences among tillage systems should prove useful in optimizing fertilizer use and crop yields.
Conventional till is often considered to be tillage that inverts the soil and has become relatively rare in Montana over the past few decades. Minimum tillage systems leave crop residue on the field, providing 15 to 30 percent surface coverage and causing minor soil disturbance. Examples of minimum till systems include:
• stubble mulching (tillage that leaves stubble on the soil surface)
• fewer tillage passes
• sweep tillage
• strip tillage
In addition, surface residue coverage increases further as tillage intensity decreases (e.g. ridge till and mulch till), with maximum surface residue coverage in no-till systems.
In 2004, approximately 28 percent of Montana’s cropland was no-till, whereas 22 percent was in minimum till (CTIC, 2004). The large conversion to either no-till or minimum till occurred because these systems offer several advantages over conventional till systems. For example, conversion to no-till and minimum till systems can increase crop yields, save on fuel costs, reduce soil erosion and decrease water runoff.
Research has shown that no-till and minimum till systems influence:
• water infiltration
• soil moisture
• soil temperature
• nutrient distribution (or ‘stratification’)
• soil aeration
• microbial populations and activity
These factors each affect soil nutrient availability. Information in this guide will help producers and their advisers optimize nutrient availability and crop yields in both no-till and minimum till systems.
Two nutrient cycling processes, nitrogen (N) “mineralization” and nutrient “stratification,” appear to have the highest likelihood of being affected by the degree of tillage. This guide will focus on these two processes.
Soil organic matter (SOM) is composed of decomposing plant and animal residues, cells and tissues of soil organisms and well-decomposed substances. Though living organisms are not considered within this definition, their presence is critical to the formation of SOM. For example, crop residue is converted to stable SOM by the action of bacteria, fungi and larger organisms (e.g., rodents and earthworms). In breaking down both crop residue and SOM, organisms release plant available nitrogen (N) in a process called “mineralization.”
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