Introduction

Flood meadows are an extremely important forage resource for beef cattle and hay producers. Over 3 million acres of flood meadows exist in the western United States, with these lands producing the majority of winter feed for beef cattle.

Snowmelt from surrounding mountains provides annual flooding, which typically lasts from April to late June. Initially, these native flood meadows were composed of a mixture of rushes, sedges, grasses and forbs. Historically, these native plants produced approximately 1.6 ton/acre (Rumburg, 1961), with all of the production occurring during the short flooding period in the spring.

Fertilization research with the native meadows suggested that 60 units of nitrogen was the most economical level and could be expected to increase forage yield by approximately 3/4 ton per acre (Angell, 1998). In this earlier work, the source of nitrogen was not critical and the general recommendation was to use the source of nitrogen that gave the lowest cost per pound of nitrogen.

However, in an effort to increase forage yields, an introduced grass species, meadow foxtail, was introduced into many meadows in the western United States. This highly competitive grass has since become the predominant grass species in high-elevation flood meadows throughout the west. Consequently, research was conducted to determine the most appropriate level of nitrogen fertilization to economically increase forage yield in flood meadows dominated by meadow foxtail.

Experimental procedures

In March of three years (1995, 1996, and 1997), 48 plots within a meadow foxtail-dominated meadow were fertilized with 0, 36, 72, or 108 lb of nitrogen/acre, applied as urea during March of each year. Forage yield was determined at three consecutive weekly intervals each year beginning as soon as the ground was dry enough for haying equipment.

Initial harvest dates were 17 July 1995, 9 July 1996, and 10 July 1997. On each harvest date, a swather was used to harvest forage. A known length of each windrow was weighed and dry matter determined for estimation of forage yield.

Outcomes

How much does nitrogen fertilizer increase forage yield?

Meadow foxtail responded to nitrogen fertilization with a linear increase in forage yield in each of the three years (Figure 1). On average, the increase in forage production was approximately 24 pounds of forage dry matter/unit of nitrogen. Therefore, if we fertilized with 60 pounds of nitrogen/acre we can expect an increase of approximately 1,440 pounds of forage dry matter (24 × 60 = 1,440) compared with no fertilization.

Does previous year's irrigation influence response to nitrogen fertilizer?

The magnitude of response to nitrogen fertilization appeared to be related to previous years' growing conditions. For example, the first year of the study (1995) had a good supply of irrigation water but this occurred following a period in which 4 of the previous 5 years were drier than average and no irrigation water was applied to the meadow during this five-year period.

In 1995, the increase in forage production due to nitrogen fertilization was only about 50% of that seen in 1996 and 1997, both of which followed a wet, or good, irrigation year. In 1995, we observed a 13.6 pound/acre increase in forage production per unit of nitrogen compared with a response in 1996 and 1997 of 27.8 and 31.0 pounds of forage/acre increase, respectively, for each pound of supplemental nitrogen. Therefore, it seems from this limited data set that there is a greater response to nitrogen fertilization following a wet year than following a dry year.

Table 1 provides estimates, based on the data available, of the expected increase in forage production at nitrogen fertilization levels of 20 to 110 pounds/acre for fertilization following a dry year, a wet year, and the “average” of all (3) years. However, please keep in mind that the response difference between “dry” and “wet” years is based on information collected over a three-year period, with only one measurement following a dry period.

Therefore, there may be significant annual variation in the magnitude of your observed response to nitrogen fertilization. Nevertheless, we feel that the data does indicate that fertilization with up to approximately 100 pounds of nitrogen/acre will increase forage production in a linear manner, regardless of the previous irrigation season, assuming there is adequate irrigation water.

Will fertilization enhance hay quality?

Fertilization of Oregon flood meadow did not significantly change the crude protein content of meadow foxtail hay. The absolute value actually showed a decreasing trend with added nitrogen (Figure 2). We attributed this to an increase in the production of stem relative to leaf material.

These trends are generally consistent with other studies (reported in Rumberg, 1961), where crude protein was not increased following nitrogen fertilization. The bottom line seems to be that yield will be significantly increased however hay quality will be similar to unfertilized meadow hay.

When is it economical to apply nitrogen fertilizer?

This is the question that we all seem to face, especially with high hay, fertilizer, fuel, and labor costs. Therefore, based on the information presented above, we have come up with some estimated breakeven costs for fertilization with urea or ammonium sulfate at forage values ranging from $130 to $200/ton (Table 2). In addition, the breakeven price of the nitrogen fertilizers is provided based on the overall average, following a dry year, and following a wet year.

An example of how to use this table is provided. Let’s assume that last year was a wet year with adequate irrigation water. In addition, your local hay market forecast indicates that meadow hay will be selling for $170/ton. Therefore, the breakeven price for urea would be $2,136/ton and for ammonium sulfate it would be $996/ton.

This means you could afford to pay up to these amounts for the respective fertilizers (including application costs) and expect to breakeven. If the fertilizer and application costs are greater than these values it does not pay to fertilize and it would be cheaper to purchase the additional hay from someone locally.

It is possible to use the three categories in Table 2 to manage the risk/reward status of your fertilizer investment. For instance, if you had used the “average of years” values rather than the “following wet year” values in the example above this would have been a more conservative choice because the breakeven values would have been $1,845/ton and $861/ton for urea and ammonium sulfate, respectively compared with the $2,136/ton and $996/ton. Likewise, you could use the “following dry year” breakeven values as a worst-case scenario ($1,041/ton and $486/ton).

Conclusion

Nitrogen fertilization of meadow foxtail-dominated flood meadows will increase the quantity of hay produced with little effect on forage quality. Also, our data suggests that the availability of irrigation water in the year prior influences the magnitude of the increase seen in forage production attributed to nitrogen fertilization, with a greater increase in forage production following a “wet” year compared with a “dry” year.

Consequently, the economical benefit of nitrogen fertilization is dependent on a number of variables including cost of fertilizer, forage value, and the magnitude of response to fertilizer. This article provides producers with the tools necessary to make informed decisions concerning when and how much nitrogen to apply to meadow foxtail-dominated flood meadows.

References

• Angell, R. 1998. Rangeland Science Series Report #4. Oregon State University, Corvallis.
• Rumburg, C. B. 1961. Misc. paper 116. Oregon Agricultural Experiment station, Corvallis, OR.