GHGMP Project Reports by Region

Spring soil test can help trim fertilizer bill

Using spring soil nitrate tests will help producers make best use of nutrient resources

Minimize nutrient waste, save crop input costs and reduce the impact on the environment. Those are the three main benefits a spring soil nitrogen test can provide farmers in Eastern Canada, says a Nova Scotia soil conservation specialist.

Evaluations of five on-farm demonstration sites in 2003 showed soil tests can be a valuable tool for matching nutrients with crop requirements, says Rob Michitsch, regional co-ordinator of the federal Greenhouse Gas Mitigation Program for Canadian Agriculture (GHGMP).

The demonstration sites, located throughout Nova Scotia, were used to compare the benefits of pre-plant soil nitrate testing in both grain and corn crops. The demonstrations are among a number of projects funded in part by the GHGMP.

Manure counts

Demonstrations showed that on land receiving manure at recommended rates, producers can eliminate the cost of added commercial nitrogen and still maintain yield. At the same time, the reduced nitrogen loading also dramatically reduced production of nitrous oxide, a harmful greenhouse gas.

"Most producers simply follow traditional nitrogen fertilizer recommendations, which do not consider residual nitrogen available to the crop during the growing season," says Michitsch (pronounced Mikitch). "Soil nitrate testing isn't commonly done in Atlantic Canada, partly because of the wet climate and also because this type of testing has not been demonstrated in the region."

Through this and other demonstration projects it's hoped that the reliability of these tests can be demonstrated and more producers will adopt spring soil testing as part of their overall crop and nutrient management planning.

Ongoing demonstration

In the first year of three years of demonstrations, variable fertilizer rates were applied to barley, wheat and corn crops at all five locations. Soil nitrate tests were done on each plot just prior to planting, during the growing season and after harvest. Fertilizer rates ranged from 25 percent to 100 percent of recommended rates. The standard recommended rates for commercial fertilizer are up between 115 and 130 kilograms per hectare of nitrogen for corn and up to 70 kilograms per hectare for barley. There were also control plots with no added nitrogen at all locations.

The on-farm demonstration sites in western Nova Scotia had no recent history of manure application, says Michitsch, while sites in eastern Nova Scotia had received manure regularly over several years.

"Sites with little or no manure showed a positive yield response to applied fertilizer," he says. "However, the site receiving two heavy manure applications a year showed no significant yield differences when additional nitrogen fertilizer was applied."

This means if soil has a high nitrogen content from prior manure application, no added fertilizer is needed. "That's the benefit of the spring soil nitrogen test," he says. "It can indicate the level of nitrogen is present in the soil, allowing a producer to efficiently adjust their fertilizer application rates to avoid the application of excessive nitrogen above crop requirements."

Reduce inputs, benefits environment

Reducing nitrogen application not only reduces input costs to producers, but also means more efficient use of the nitrogen that is available. Nitrogen left in the soil can leach away over winter and during heavy rainfall. It can also be lost to the atmosphere through a process known as denitrification. Nitrate remaining in the soil can be converted to nitrous oxide, which is one of the more serious greenhouse gases.

Plots at an eastern site, which had a long history of manure application, showed similar barley yields, whether or not nitrogen fertilizer was applied. All sites yielded about 2.5 tonnes per hectare.

The sites in western Nova Scotia, with no recent manure application, showed that wheat yields increased when up to 50 percent of the recommended fertilizer rate was applied. Beyond that, added nitrogen produced no significant yield increase. The next 35 pounds of nitrogen, for example, didn't result in enough additional yield to pay for the fertilizer. "Even without manure, we found maximum yields could be obtained with half the standard fertilizer rate," says Michitsch. Wheat yields at a western sites were up to about 3.5 tonnes per hectare.

Test tells the story

"What these demonstrations show is that with a spring soil test, a producer can better match nitrogen applications with crop requirements," says Michitsch. "On previously manured land, we showed that additional nitrogen may not be needed to achieve maximum crop yields. On non-manured land, we showed that reduced levels of the recommended fertilizer rate were sufficient to meet crop requirements for maximum yields. However, our results are specific to individual sites; a producer must test their own fields in order to properly adjust their rates of fertilizer application."

From a greenhouse gas emission standpoint, the amount of nitrous oxide produced was considerably higher on plots receiving nitrogen in excess of crop requirements. For example, on the eastern plots, which had received high rates of manure application as well as added fertilizer, nitrous oxide levels were high. On western plots, which had not received manure, nitrous oxide levels were reduced by as much as 80 percent when nitrogen fertilizer application rate was reduced.

"Using a soil nitrogen test to adjust nitrogen fertilizer application rates allows a producer to avoid excessive application of nitrogen," says Michitsch. "This improves profitability while helping to reduce potential environmental impacts, such as nitrate leaching to groundwater sources large emissions of greenhouse gases."

For more details on this demonstration project, obtain a copy of the fact sheet: Nitrogen Fertilization Based on Pre-plant Soil Nitrogen Testing for Grain and Pre-sidedress Soil Nitrogen for Corn, produced by Nova Scotia Agricultural College and Soil and Crop Improvement Association of Nova Scotia.


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