by Justin Brackenrich

Nitrogen is one of the most essential nutrients for perennial grasses and will almost always result in increased growth and production.

But how much nitrogen should be applied? What is the right source, at the right rate, at the right place and at the right time? A small plot study this summer in Washington County, Pa., is looking to answer those questions.

Twelve 22-by-75-foot plots are assessing the effects of different nitrogen fertilizers applied at different rates. Sources include urea and polymer-coated nitrogen.

Urea is a standard nitrogen source with an analysis of 46-0-0. A drawback is that it can be lost to volatilization if not applied before rain, or as a stabilized product.

SAMPLE CUTTING: On the left is a sample from the control plot. On the right is a sample from a plot that had a single application of urea. Twelve 22-by-75-foot plots in Washington County, Pa., are assessing the effects of different nitrogen fertilizers applied at different rates.

Polymer-coated nitrogen is a slow-release product with resistance to volatilization. It provides N throughout the season as the polymer coating slowly breaks down. The product used in this trial has an analysis of 44-0-0.

When using a polymer-coated N product, the manufacturer recommends applying 20% to 30% of recommended N as a faster-releasing, more available product like urea or ammonium sulfate. For example, if you apply 100 nitrogen units, 70 should come from polymer-coated N, while 30 should come from urea or ammonium sulfate.

Application timings

The timing comparison includes different rates for green-up and split applications after cutting.

Here’s a breakdown of the four treatments, which are replicated three times:

First cutting results

The control plots remained thinner and yellow in May compared to the treated areas. There was also a difference in speciation in the control and treated plots.

Sweet vernal grass, Kentucky bluegrass, plantain species and dandelions dominated the control plots, while the treated plots had a greater concentration of orchardgrass, tall fescue and ryegrass. Some perennial weeds were still in the treated plots, but concentrations were much lower.

Samples were harvested May 20. Two samples were collected per plot. Part of the sample was air-dried, weighed and processed through a Koster Tester, and then reweighed for dry matter calculation. A smaller sub-sample was air-dried and sent to Cumberland Valley Analytical Services Lab for forage analysis.

Hay was removed around May 25, allowing for a second application of potash and urea (on split-applied treatments) on May 29. 

Second cutting results

Second cutting was inconsistent. Depending on treatment, the plots produced between 400 and 1,400 pounds of hay per acre.

Control plots were on the lower end, while environmentally smart nitrogen and urea-treated plots were on the higher side. What can be interpreted from this? A better fertility program on cool-season grasses will provide better opportunities for production during periods of high heat and drought.

The control plots’ average crude protein and relative feed value values were 9.9% and 106, respectively. The average value of crude protein and RFV for the ESN and urea were 12.8% and 110, respectively.

What does this tell us? First, there was a dramatic difference between clover and orchardgrass in the ESN and urea-treated plot, in comparison to the plantain and weed-dominated control plot.

Second, protein is nitrogen. This may be an oversimplification, but plant protein will be reduced if soil and available N are lacking. This was apparent in these samples. In the control, where no N was applied, protein is 9.9%. However, as the ESN is still slowly released, it provides the N needed to increase the protein content in the grass.

Putting pencil to paper

Most research or fact sheets related to cutting grass hay in a drought situation recommend cutting only if it is cost-effective. But how do we know what is cost-effective?

Quite a few factors influence this decision, and ultimately, it is something that all producers will have to decide on their own. In this case, we chose to rotary-mow the plot rather than harvest for hay. The plots were rotary-mowed at a height of 5 inches to clip the tops of weeds and release new tillers.

With the combination of rotary mowing and little top growth, there is very little remaining residue that will cause issues in the next harvest.

I will explain how we came to this decision.

Pricing can be considered two ways: price per bale or per acre. Either way, the more bales produced, the higher the cost, but the less the price per ton of hay produced. For this project, we used price-per-acre rates.

Based on custom rates in the mid-Atlantic, it costs an average of $55 an acre to mow, ted, rake and round-bale (about 600 pounds or 3 bales per ton). The control produced 0.2 ton per acre of hay, or less than a bale an acre. This costs $275 a ton to just harvest and bale.

For the split application of urea, production was 0.7 ton per acre of hay, or two bales per acre, with a production cost of $98 a ton, which includes the additional fertilizer cost. We also considered the amount of nutrients removed in the harvest that may be returned to the soil during decomposition.

Finally, we assessed the field's total production, not just the plot area. It would have been economic if the entire 3-acre field yielded two bales an acre. However, there was only about one-quarter acre yielding this high, while the remaining 2.75 acres yielded less than a bale an acre.

The argument can be made that any hay is better than no hay. But is that true?

Based on the hay auction in New Holland, Pa., good-quality prairie or meadow grass was sold for $190-$250 a ton. Good quality has a crude protein of 9% to 13%. Understand that shipping and other fees are involved, but still, this is something to consider.

Brackenrich is an Extension educator of field and forage crops with Penn State Cooperative Extension.

Source: Penn State Cooperative Extension