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Attempting to reduce soil P levels in manured fields

Incorporating variable rate fertilization into cropping systems.

March 5, 2008  By John Harapiak

Figure 1. The information contained in the legend confirms that the five map zones in a field with a long history of manure
application have unique soil characteristics. Zone 1 is the least productive due to low organic matter levels and soil erosion. The highest rates of N fertilizer are applied in Zones 3 and 4. Zone 5 has high levels of residual nutrients, is very prone to lodging and will receive no N fertilizer.

The current Alberta manure application guidelines are based on the N content of the manure. However, some growers and crop consultants are going beyond meeting this requirement in developing their manure management plans. While an excessive build-up of N from manure applications can create a serious environmental concern, they realize that a build-up of soil P from repeated applications of manure could potentially create a more serious soil management problem for them.

Hog production has been a key component of the Neufeld Farms operation for many years. This 2700 acre farm located near Acme, Alberta, markets between 10,000 and 15,000 hogs per year. The three million gallons of liquid manure that is produced each year plays a very important role in the fertility program for the cereal and canola crops that are grown. In the past, for economic reasons, manure application tended to be focussed on fields that were located closer to the hog operation. This resulted in elevated levels of soil P and chronic lodging problems that were of concern for farm owner Albert Neufeld and his crop consultant, Steve Larocque.

Neufeld has used the services of CCA crop consultant Steve Larocque, of Beyond Agronomy, to assist in the development of his soil fertility and crop management strategies since the fall of 2003. Larocque found that soil sampling of manured fields provided results that were inconsistent and difficult to use for developing fertility recommendations. Therefore, he changed to using a series of benchmark soil sampling sites for monitoring year-to-year changes in soil fertility status.

Grower Albert Neufeld and CCA crop consultant Steve Larocque review
variable rate fertilization that has
been developed for a field with a long history of manure application. They have decided to continue with the
elimination of fertilizer P applications in an attempt to draw down the excessive soil P levels.

More recently, Larocque has switched to using a zone based soil sampling approach for developing a recommended variable rate fertilization program. The zones are developed from NDVI images (normalized differential vegetative index) purchased from Farmer’s Edge, which is a variable rate management company located in Pilot Mound, Manitoba.

Neufeld uses a Flexi-coil 5000 air-seeder that is equipped with a triple tank. He indicates that this unit provides him with the flexibility required for conducting variable rate fertilization. He indicates that, “In manured fields, one tank could be used for seed, another for urea-N and the third for a custom blend. Depending on the soil test results, we may use two tanks for urea or two for seed.” He adds that, “This coming year we are testing out a precision, zone based fertilization program where we will vary the fertilizer throughout a field and, if it works well, we may vary the fertilizer rates on the whole farm next year.”

Neufeld indicates that in working with a crop consultant, he wanted to assure himself that his manure based fertility programs were environmentally sound, improve the uniformity of his crops and reduce the degree of the chronic crop lodging that was occurring in some of the potentially most productive areas of his fields. In 2004, with guidance from Larocque, he embarked on a program of manual variable rate fertilization for his fields and increased the emphasis on the selection of crop varieties with improved standability.

There were several important issues that needed to be addressed. Larocque’s zone based soil sampling revealed that the lodged areas, (especially in the manured fields) contained the highest levels of N, P, K and S. They therefore made the decision to either reduce or eliminate fertilizer application in those areas in order to reduce the risk of crop lodging and to draw down the surplus nutrients present in the soil.

This unit will be used to spread five tonnes per acre of a compost-gypsum-liquid hog manure mixture on some of eroded, less productive soil zones
located in some of Albert Neufeld’s fields. A Fendt tractor is pulling an Artex spreader, which can hold 15 tonnes. This GPS equipped unit can spread rates as low as one tonne per acre in a 30 foot spread pattern. Holtrop Enterprises of Lacombe does this
custom work at a rate of $135 per hour which, depending on the rate of application, works out to $2.50 to $5.00 per tonne.

Secondly, zone based soil sampling revealed that soil P levels were excessive in the fields with a longer history of manure application. The decision was therefore made to eliminate the application of both P fertilizer and liquid hog manure in those fields. It was also decided that Larocque and Neufeld would closely monitor soil P levels and yields in those fields to determine if and when adjustments to these fertility plans would be required. In addition, a plan has been developed to apply the liquid hog manure to fields located further away from the hog operation.

After four years of following this program in the fields with a long history of manure application, it appears that the ‘no fertilizer P’ program appears to be working. As illustrated in Table 1, after four years of the adoption of the ‘no fertilizer P’ program, the yields achieved by the canola, wheat and barley crops have been quite satisfactory. More surprising has been the very significant draw down in soil P levels that have been achieved in a relatively short period of time. Larocque does not expect that additional reductions in soil P will be as easily achieved.

One additional aspect of yield variability that is going to be addressed is the lower crop production that is associated with some eroded ridges that are lowest in organic content (see Zone 1 percent organic matter in Figure 1). Plans are underway to apply five tonnes per acre of feedlot compost amended with gypsum and liquid hog manure in those lower yielding areas in an attempt to build-up soil organic matter and subsequently increase crop production.

Early in his crop consulting business, Larocque had a stated objective of
providing timely, relevant and accurate crop production advice to enable his clients to make better farming decisions. He also saw an opportunity to provide a useful service to his clients by providing weekly, in-season updates on weeds, insects, diseases and the economics behind the management decisions that growers faced. From there this idea developed into what’s now called Beyond Agronomy News, a weekly crop production and grain market newsletter focussing on agronomic production issues, economics and fundamental grain market news.

Larocque points out that, “The information provided in the newsletter is real-time and focussed on the daily decisions that we, as a grower and crop advisor team, are required to make throughout the year.” He indicates that it requires approximately 40 hours for him and his wife Vanessa to compile the weekly newsletter that is published 46 times per year. Both Steve and Vanessa are ag-grads from the University of Lethbridge. Subscription information and past issues of Beyond Agronomy News can be viewed at -end-

Table 1. Crop yields achieved and rate of draw down of soil P in highly manured fields with no application of fertilizer P.
 Year Soil P (lb/ac)
Crop grown
Yield (bu/ac)
 2004 94 Hyola 505 canola 50
2005 82 AC Harvest wheat 75
2006 73 AC Harvest wheat 67
2007 62 Xena barley 98
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Steve and Vanessa Larocque jointly work on the formatting of the latest Beyond Agronomy newsletter. Vanessa refers to this teamwork effort as their ‘together project’. Steve states that, “While the internet is a very useful
tool for accessing large amounts of  information that is relevant to prairie farming from all around the world, most growers do not have the time nor the inclination to search for this information.”
Top Crop Manager regularly carries a story featuring certified crop advisers from various regions of western Canada. There are more than 700
individuals who have achieved the certification and maintain this designation through
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