Page 283 - Nutrient Management Planning Guide

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Chapter 8.2

more info

AF has over 30 publications relating to direct seeding and reducing tillage, including: 1996. Soil quality and •

moisture conservation benefits of direct seeding. Agdex 570-6. 1999. Direct seeding systems: •

terms, definitions and explanations. Agdex 570-7. 2006. Making the move to •

direct seeding. Agdex 570-5. Another excellent resource is Reduced Tillage LINKAGES (www. reducedtillage.ca), which has a network of specialists throughout Alberta that can provide advice on issues relating to reduced tillage production systems. The Prairie Farm Rehabilitation Administration (PFRA) with AAFC also has information relating to reduced tillage in the following online documents: Brandt, S. 2006. Tillage •

practices that reduce soil erosion. www.agr.gc.ca/ pfra/soil/tillage_e.htm PFRA. 2006. Economics of •

zero till. www.agr.gc.ca/ pfra/soil/ swork1.htm

Fallow Systems

Negative Impacts of Fallow » Fallow systems result in decreased organic matter •

levels with time since little plant residues are returned to the soil during fallow years. Tillage raises soil temperatures and increases •

aeration and mixing of the soil, which increases the rate of decomposition of soil organic matter and crop residues compared to a soil with a growing crop. Declining soil organic matter content degrades the physical structure or tilth of the soil. Poorer soil structure results in less infiltration of precipitation into the soil resulting in increased runoff, further increasing the likelihood of soil and nutrient losses. Lack of plant residues on the surface as a result of •

repeated tillage operations leave the soil vulnerable to water (and wind) erosion. All fallow systems increase the risk of nutrients •

being lost from the soil through volatilization and leaching. Loss of crop available nutrients. As organic matter •

and crop residues decompose, soil microorganisms mineralize organic forms of crop nutrients to crop-available forms. Normally, these mineralized nutrients would be taken up by growing crops but in fallowed fields they remain in the soil and may be lost either through leaching or gaseous emissions. Impact on groundwater recharge. Crop plants •

are large consumers of soil moisture and play an important role in regulating soil moisture conditions. Under fallow conditions, more precipitation percolates down through the subsoil and enters the groundwater. This can transport water-soluble crop nutrients (e.g., nitrate) to groundwater sources and impact groundwater quality. Downward movement of water can also move salts to groundwater discharge areas causing groundwater levels to rise in these discharge areas and potentially increase salinity.

Conservation Fallow

Conservation fallow maintains plant residues on the soil surface, which helps to reduce soil erosion while still providing weed control and soil moisture conservation benefits. With no tillage, stubble and other residues from the preceding crop are left undisturbed, erect and anchored, as are the remains of the dead weeds. This practice protects the soil from wind and water erosion and increases snow catching. The shade provided by the residues keeps the soil surface cooler and together with less tillage-induced aeration of the soil reduces evaporation.

At the end of summer fallow period, typically 60 to 80% of the protecting stubble remains. Losses during this period are due to the normal decomposition from ultra-violet radiation, chemical oxidation and microbial activity.

Winter Cereal Production or Cover Crops

Another strategy for maintaining ground cover during periods of high runoff risk from snowmelt is to include winter cereals in crop rotations or selectively planted in vulnerable areas. Winter cereals begin growing and using nutrients in the fall reducing the opportunity for the loss of applied nutrients (i.e., manure or fertilizer) later in the season. Even though winter cereals do not grow much during the winter, the crop prevents free flow of snowmelt water in the spring and the roots anchor soil particles. This reduces the risk of erosion and sediment-bound nutrient losses in the spring. Later in the season, winter cereals provide ground cover that buffers raindrop impact during rainfall events helping to preserve soil structure and reduce the risk of soil erosion.

Fall rye has the best winter hardiness and produces the most soil cover followed by winter triticale and then