STEP 5 Determining Acceptable Application Rates
Safe rates of manure application depend on the nutrient value of the manure, nutrients available in the soil, and the expected nutrient uptake of the crop to be grown (Saskatchewan Agriculture and
STEP 5 Determining Acceptable Application Rates
Safe rates of manure application depend on the nutrient value of the manure, nutrients available in the soil, and the expected nutrient uptake of the crop to be grown (Saskatchewan Agriculture and Food 1997, Johnson and Eckert 1995). These values are determined by testing of manure and soil as described in Steps 1 and 2 above.
Crops requiring nitrogen, phosphorus and potassium will benefit most from manure application. Nutrient levels that exceed critical levels (Table 4) will lower crop production or threaten the environment. The health of crops planted in soils with nutrient levels below the critical levels will be agronomically compromised. Soils with nutrient levels above the critical levels represent potential contaminants for surface water and groundwater, and may cause some micronutrients to be less available to crops or be toxic to growing crops. These critical levels are still being researched, and they are provided only as guidelines, and must be adjusted based on specific field, soil and landscape situations.
Table 4. Critical Nutrient Levels (Based on Ross McKenzie, pers. comm. 1999).
|Nutrient||Critical Nutrient Levels|
|NO3-N (0-60cm) (0-24")||<56||< 50||>280-390||> 250 300|
|P (0-15cm) (0-6")||<22.5||< 20||>225-450||> 200 400|
|K (0-15cm) (0-6")||<280-390||< 250 350||>3350||> 3000|
|SO4- (0-15cm) (0-6")||<11.2||< 10||>112||> 100|
Application Rates Based on Nitrogen
Animal manure has traditionally been applied at rates designed to meet the nitrogen requirements of a crop. Previous nitrogen application rates recommended for Alberta were 30 and 60 Mg/ha (13 and 26 tons/ac) on dryland and irrigated fields, respectively. However, studies by Chang et al (1991) and Chang and Entz (1996) at the Agriculture and Agri-Food Canada Research Centre in Lethbridge found that long-term application at these rates caused significant loss of nitrate by leaching to shallow groundwater under irrigation. Chang and Travis (1995) concluded that heavy rates of cattle manure have minimal agronomic benefits for barley production, but significant negative impacts on soil, water and atmospheric quality.
In a study conducted by Alberta Agriculture in southern Alberta, the recommended annual application rate of manure with a 60% moisture content was less than 60 Mg/ha (26 tons/ac) in the short term (3-5 years), especially on coarse-textured, irrigated soils over shallow groundwater. Lower annual rates of 20 or less Mg/ha (9 tons/ac) may be required if applications are continued over a longer period (5 -10 years