Southern States News

Can You Afford To Put Out Fertilizer On Your Pastures This Year? (04/22/08)

The high prices for fertilizers have many producers scratching their heads and wondering if it is worth spending money on fertilizer this year. There are no simple answers and this article discusses the things a cow/calf producer should consider in reaching a decision.

There are five questions to be answered and the last two are the most important-how does my use of fertilizer affect the cost of feeding a cow and how does it affect the carrying capacity of my farm? The results are surprising. In the examples given below, it can take 6 acres just to graze a cow for six months if no nitrogen is applied, compared to less than two acres with nitrogen and in some cases the cost per cow can be reduced by using more nitrogen!

1) How does pasture respond to fertilizer and, in particular, to different levels of nitrogen?

Grasses do not grow well without a source of nitrogen but nitrogen is most effective when soil fertility is high. If fields have not been limed regularly and pH is low, then productivity suffers. Most grasses produce best when soil pH (acidity) is between 5.8 and 6.0. The best response to nitrogen will only happen if the pH is at the appropriate level and when all the plant nutrients are adequately supplied. This includes phosphate, potash, calcium, magnesium, and even sulfur. Soil type also affects productivity.
Regular soil and forage test (of fresh and dried forages) are required to understand the fertility status of your fields. The effects of N fertilizers are reduced when these other fertility elements are not present or supplied and money is being wasted. If cash flow is tight and puts a limit on fertilizer purchases, one strategy to consider is to only apply nitrogen to the most fertile and productive fields because these are likely to give the best response.

Several years ago, Paul Mueller and Jim Green at NCSU searched the research literature and developed a “nitrogen response curve” for fescue that showed the relationship between the amount of nitrogen applied and the amount of pasture produced. They found a range of production response to any given amount of nitrogen. With no (N) applied at all, they indicate production levels from a low of approximately 1,500 pounds of dry matter (DM) per acres up to 2,100 pounds per acre. Average production with no nitrogen was 1,800 lbs of DM per acre. This level of pasture production incurs no additional expense but far fewer cows can be carried per acre because production is so low. Production of over 8,000 lbs of DM per acre is possible with 150 pounds of N. Actual pasture in the field is 20 percent to 25 percent dry matter but we usually measure production as dry matter because dry matter contains the feed value.

These production figures refer to pure stands of fescue, but most producers have mixed stands that include other plant species, including weeds and this will affect the production response to nitrogen. Nevertheless, the general points made in the rest of the article should apply and provide a way of thinking about the fertilization decision.

2. What does additional pasture production cost?

When nitrogen was applied, Mueller and Green found that fescue pasture production increased between 27 to 33 pounds of dry matter for every pound of actual nitrogen applied, up to 150 pounds of N. The average response was approximately 30 pounds of pasture dry matter per pound of nitrogen. For example, at 100 lbs of N, the response was 5,450 to 4,200 pounds of pasture dry matter, and increase of 2,700 to 3,350 pounds, respectively, over the amount of production with no added nitrogen. Different nitrogen fertilizers contain different amounts of actual nitrogen, so these figures are based on the pounds of actual nitrogen applied.

In a situation where soil fertility is high, no lime or other plant nutrients may be needed this year. However, soil fertility will be reduced and this is not a sustainable strategy long term. If nitrogen costs 50 cents a pound, then the cost of an additional pound of pasture dry matter is approximately 1.67 cents. At 75 cents per pound of N, the cost of the additional pasture is 2.5 cents, and at 90 cents per lb of N, the cost of additional pasture is 3 cents per pound. These are pasture production costs and do not allow for wastage during grazing, added costs of making hay, managing grazing, etc., which can easily double the actual cost of the pasture a cow actually eats.

However, if soil fertility is low and lime and other nutrients are needed, this cost must be considered also and will raise the cost of the resulting pasture at all levels of production. These costs are considered in the following paragraph.

3) What is the average cost of producing pasture?

Table 1 shows the cost of production per pound of pasture dry matter with three different nitrogen prices with and without an additional cost of $60 per acre for P, K, lime, and other nutrients needed to get a nitrogen response and maintain soil fertility. However, the amount of plant nutrients and their cost will vary depending on the field and the fertilizer source. As you can see, the production cost varies widely between these various situations, from zero to 3.3 cents per pound of dry matter. There is a comparable effect on the cost of feeding a cow.

4. What does it cost to feed a cow?

In Table 2 we used the pasture costs from Table 1. We assume that a cow needs to EAT 30 lbs of dry matter per day and that the fescue pasture will provide 180 days of grazing. We also assume that cattle are given access to a large area of pasture and moved infrequently, causing 50 percent of the pasture to be wasted through tramping and spoilage. Note that rotational grazing can reduce wastage to perhaps 20 to 25 percent, but it adds to the time invested and some expense and this will affect the total cost.

If soil fertility is high and no lime or other nutrients are needed, then clearly the cost per cow is lowest with no fertilizer. With nitrogen application, only the cost is $122 to $207 per cow, depending on the cost of fertilizer and the application rate. However, if lime, P, and K are applied at a cost of $60 per acre, then the no nitrogen scenario is the most expensive, (though it is unlikely someone would apply these nutrients and not apply nitrogen as well). Applying more nitrogen actually reduces the cost per cow because the $60 per acre cost is spread over more total pasture production. The higher N rate ¬-150 lbs per acre- actually is the cheapest system per cow in this example.

5. How many acres are needed to feed a beef cow?

We took the same feed scenario -30 lbs of DM per cow per day, 180 days of available grazing, and 50 percent waste- together with the yield response figures from Mueller and Green to figure how many acres it would take to graze a cow. We were amazed at the answers. With no nitrogen applied, it takes six acres per cow just for grazing! Note that in these calculations there is no allowance for pasture cut for hay – total pasture production is all grazed. At 100 lbs of N, it take 2.2 acres per cow and at 150 lbs of N, it takes 1.5 acres. So, if you have 100 acres for grazing, then the range in carrying capacity is from a low of only 17 cows on 100 acres of grazing to a high of 65 cows on 100 acres. The key point is that you must match your carrying capacity to your fertilizer decisions. Many producers have reduced their cow numbers because of the drought and the fertilizer decision should be part of the decision about restocking.

A final consideration is risk. No rain, no grass! These calculations are all based on getting adequate rainfall.

The “bottom line” is that cow/calf producers must think through the nitrogen fertilizer decision to where it matters – feed cost per cow and the carrying capacity of the farm under different fertilizer scenarios. These are only examples, but we hope they are realistic ones in that they cover a range of possibilities – provided, of course, that we get rain when we need it.

One final point is the net income figures for many if not most producers will be seriously in the red this year. We are in a high cost of production situation for the foreseeable future, even with rain, and losing money this year in the hopes of a turnaround down the road likely is not warranted. There are different situations and different production systems, and we expect some producers can reach a point where the economics are acceptable. However, some producers may need to face up to the fact that cattle production is not a viable option for them under the current costs of production.

THE CAROLINA CATTLE CONNECTION – APRIL 2008

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