Fertilizing fields with manure can increase moisture retention and reduce compaction.
Studies at the Agriculture Canada Research Centre in Lethbridge, Alta., have found that manure increases the amount of water that stays in the root zone, which is the first 100 centimetres of the soil surface.
Increased water retention can improve soil moisture and may have an indirect benefit on crop growth, said researcher Jim Miller, who conducted the study with Chi Chang.
“Applying manure to the soil increases the amount of soil organic carbon, which allows the soil to soak up more water,” Miller said.
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“So the more soil organic carbon you have, the more water you can retain. That may result in the crop being able to utilize more water, particularly under dryland conditions.”
The scientists also found that manure reduced soil compaction in the top 15 cm.
“Soil compaction is an undesirable soil condition that makes the soil more dense and reduces the larger pores, which makes root growth, and water and air flow more difficult.”
While manure’s nutritional benefits are known, Miller said the effects on soil are a key finding.
The Alberta cattle industry alone produces more than 660,000 tonnes of manure a year. Spreading it on fields has become an important way to use manure and reduce its potential as an environmental hazard.
Knowing how manure affects the land when applied at different rates can improve how it is used.
The study was conducted on the research centre’s long-term manure research site, where scientists have measured the impact of manure applications on both dryland and irrigated plots since 1973.
As well as studying water retention and compaction, scientists set up methods to measure a range of other soil properties.
“The specific effects of manure rate on other certain soil physical properties is complicated and varies depending on the year, soil depth, season and soil moisture content,” Miller said.
“But the important thing is we know there can be significant benefits for certain soil physical properties in addition to the benefits of manure as a nutrient resource.”
A new study by Miller and colleague Frank Larney will compare soil physical properties under different rates of fresh manure and compost containing straw or wood-chip bedding material.
Manure has traditionally been spread when it is fresh, but composted manure is becoming more common. In addition, while straw has traditionally been the most common bedding material used in feedlots, wood chips are gaining popularity.
As a result, information is needed on the potential impact of these new manure products on the physical condition of the soil.
