An important part of efficient livestock production is ensuring there is sufficient grass for hay and pasture.
Forage production, however, is often limited by low soil nutrient levels. With good soil fertility and fertilizer management, the productivity of many hay and pasture fields can be greatly improved.
When determining soil fertility, consider a number of factors.
- Brown and dark brown soils in southern and east-central Alberta are often deficient in nitrogen. These soils are also often moderately deficient in phosphorus, but rarely deficient in potassium and sulfur.
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- Black, grey-wooded and grey-black transition soils in central and northern Alberta are commonly deficient in nitrogen and phosphorus and occasionally deficient in potassium and sulfur, particularly in sandy soils.
“Grass has a relatively high demand for nutrients,” said Ross McKenzie, research agronomist with Alberta Agriculture at Lethbridge.
“Grass grown under irrigation or with optimum precipitation and nutrients is capable of producing high annual yields of over five tons per acre. However, under dryland rain-fed conditions, yields of 1.5 to four tonnes per acre are more common.”
Nitrogen is often the most limiting nutrient in grass production across Alberta. A three-tonnes-per-acre grass crop will remove 90 to 100 pounds of nitrogen per acre.
There is little research data available on the economic rates of nitrogen fertilizer for grass production in Alberta.
Microbial activity and the rate of nitrogen release from soil organic matter are influenced by environmental conditions such as soil temperature, soil moisture and organic matter.
Nitrogen released from soil organic matter decomposition during the growing season supplies only five to 20 percent of the total nitrogen needed for grass production.
Well-aerated soil with higher levels of organic matter will release more plant-available nitrogen.
Compacted soils with low soil organic matter will release little plant-available nitrogen.
Brown and grey-wooded soils mineralize the least amount of soil nitrogen. For optimum production, the amount of nitrogen required above that supplied from organic matter decomposition must be supplied by fertilization.
Optimum levels of grass production require adequate levels of soil phosphorus, and most soils in Alberta are naturally low in plant-available phosphorus.
However, residual levels of phosphorus in soils will vary depending on past phosphate fertilizer use and manure management practices.
Fields that have received phosphate fertilizer or manure application for a number of years often have good residual soil phosphorus levels and may not require additional phosphorus.
“Grass also needs potassium, sulfur, calcium, magnesium and micronutrients,” McKenzie said.
“Most Alberta soils have adequate-to-high available soil potassium. Intensively cropped sandy soils tend to be deficient in potassium and sulfur.
However, deficiencies tend to occur more commonly in black soils, grey-black transition soils and grey-wooded soils in central and northern Alberta.
Deficiencies rarely occur in brown and dark brown soils in southern and east-central Alberta.
Soil testing helps identify deficiencies in potassium or sulfur.
Further research is needed to accurately determine when grass will respond to added potassium or sulfur fertilizer.
There are no scientifically documented reports of calcium or magnesium deficiencies with forage crops on Alberta soils.
Field soil sampling and testing are important tools for assessing soil fertility and developing proper fertilizer recommendations. They are also valuable for monitoring soil changes resulting from management practices or diagnosing specific grass production problems.
“Through good fertilizer management, the productivity of many hay and pasture fields can be significantly improved,” McKenzie said.
Soil fertility levels should be monitored throughout the life of a grass stand to ensure optimum production.
Plant tissue analysis may provide useful information on soil fertility and the nutritional health of a grass crop. Grass tissue analysis can determine the nutritional levels of the crop before visual symptoms of deficiency appear.
Tissue analysis, coupled with soil tests, can make for a more comprehensive fertilizer management program for grass.
For more information, refer to the new publication Fertilizing Grass for Hay and Pasture Agdex 127/541-1. This publication is available on-line or contact the Alberta Ag-Info Centre toll-free in Alberta at 866-882-7677.
Further information on plant tissue sampling procedures can be obtained from a soil-testing laboratory.
For micronutrient recommendations, sources and methods of application for grass production on problem soils, consult a soil or forage specialist and review Micronutrient Requirements of Crops, Agdex 531-1.
This is available on Alberta Agriculture’s website or a copy can be obtained from Alberta Agriculture’s Publications Office by calling toll-free 800-292-5697 or 780-427-0391 in the Edmonton area.
