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Cropping Practices to Reduce Nutrient Losses in Runoff

Practices to Maintain or Enhance Ground Cover

One of the best ways to reduce erosion is to protect the soil surface with a cover of growing plants or crop residue. Surface cover cushions the impact of raindrops so soil particles are not as easily dislodged and moved. It also slows the flow of runoff giving the soil time to absorb more water thereby reducing the total volume of runoff and risk of erosion and nutrient loss.

Crop residues and roots stabilize soil aggregates, enhance infiltration and add to soil organic matter, which increases soil water holding capacity. Ground cover also provides insulation to the soil buffering against changes in soil temperature. This has important implications for runoff resulting from snowmelt (see Chapter 8.1).

Tillage Systems

Under conventional tillage management, there are several negative impacts including reduced soil moisture reserves, increased wind and water erosion risk, disruption of soil structure, accelerated organic matter decomposition, and depending on the implement used, compaction of sub-surface soil layers.

Conservation tillage systems have been promoted in western Canada for several decades. Conservation tillage is a general term that refers to several systems including zero tillage (zero-till), direct seeding and reduced tillage. All of these systems increase the amount of crop residue left on the soil surface and all have the same goal: to minimize erosion risk and conserve soil moisture.

Minimizing the Negative Impacts of Tillage

Avoid fall tillage so ground cover is retained to •

trap snow and prevent soil erosion during the fall, winter and spring.

Replace deep tillage with shallow tillage to •

minimize disturbance of soil.

Reduce the number of tillage passes. •

Reduce tillage speed. •

Use implements that bury less crop residue •

(Table 8.2.2).

Where possible, run tillage and seeding •

operations across the slope (as opposed to up and down the slope) to prevent runoff from eroding channels down the slope.

Avoid field operations when the soil is wet. •

Table 8.2.2 Residue Left by Various Tillage Implements

Tillage Implement

% Residue Left After One Pass

% Residue Left After 4 Passes

Wide-Blade Cultivator

90 60 - 65 Chisel Plow with Low-Crown Shovel

85 40 - 45 Chisel Plow with Normal Shovels

80 35 - 40 Chisel Plow with Normal Shovels Plus Mounted Harrows

60 10 - 15

Heavy Tandem or Offset Disc

35 - 65 5 - 15 Moldboard Plow 0 - 10 0

Source: AF

tip

For crop residue to retain snow-catching effectiveness it is important that any fall soil disturbances minimize stubble knockdown and keep most of the crop residue on the surface.

more info

For recommended minimum levels of crop residue to minimize erosion (based on slope grade and length for various cropping systems and soil types), see the following online document from AF.

AF. 2005. A method for developing best management practices to prevent water erosion on farmland using WEPP. CAESA Soil Quality CSQ Research Factsheet 11. www1. agric.gov.ab.ca/$department/ deptdocs.nsf/all/sag5804