The redistribution of manure and chemical fertilizer nutrients on sloping cropland in Saskatchewan
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Organic and inorganic fertilizers in combination with water facilitate higher crop production. A major change occurring rapidly across the Prairies is the increase in intensive livestock operations. Such livestock operations generate a high volume of manure which is a recyclable nutrient source for crop production but mismanagement in field application may be of environmental concern. The present study focuses on the use of hog manure as a crop fertilizer and the potential for accumulation of residues on an undulating landscape. The purpose of this study is to assess fertilizer residues and how they change with time and space. This assessment is focused on manure and chemical fertilizer residues for different landscape positions over a one year period on a seasonal basis (spring and fall) under two different manure application rates and one chemical fertilizer application rate. The study was conducted under field conditions with normal agricultural practices of the land owner. There were three treatments: a control receiving only chemical fertilizer (spring applied); and two receiving 78.7 and 112.4 m3/ha of injected hog manure respectively (fall applied) along with a reduced chemical fertilizer application in spring. These fertilizer treatments were applied on three nearby small watersheds and the impact of the study treatments was assessed by monitoring soil chemistry, soil moisture and crop yield on different slope positions of one sample transect within each watershed. Composite soil chemical properties (EC, pH, and SAR) varied over the study period, however, the observed changes were found irrespective of the fertilizer treatments showing no adverse effect of manure application. Consideration of specific ions and elements found that chloride and nitrate concentrations increased on manure treatments as compared to the control, and the pattern of these anions can be attributed to soil moisture distribution processes on the undulating landscape as indicated by redistribution of soluble chloride and nitrate. At the end of study period (fall 2000), there was an increase in the 30-60 cm depth interval for the bottom slope positions of the manure treatments for chloride while nitrate increased on all the treatments and slope positions with a relatively higher increase on the manure treatments. For the rest of the anions (phosphate, sulphate) and cations (calcium, magnesium, potassium, sodium), the concentrations continued to vary on different dates showing no correlation with the fertilizer treatments. Levels of exchangeable calcium, magnesium, and potassium were stable showing no significant changes while exchangeable sodium was undetected. In addition a higher canola crop yield was observed on manure treatments as compared to the control receiving the chemical fertilizer, but the relative increase in crop yield was not uniform between slope positions. Generally, the concentration of fertilizer residues for different slope positions and soil depths during the study period (one year) has shown that the chemical fertilizer and manure application rates adopted by the farmer were safe for the environment and lead to above average canola yield on study transects (1611 to 2120 kg/ha) as compared to the crop district (1396 kg/ha). However, continuous use of such rates may potentially pose problem of nitrate accumulation and leaching at bottom slope position and requires further study.