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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

January - March, 2007
Forage Systems Update
Vol 16, No. 1

Objectives:
To increase the rate of gain and weaning weight of nursing beef calves in Missouri with phosphorus fertilization of tall fescue pastures.

Procedure:
Several tall fescue (K31, endophyte infected) pastures were selected at the Forage Systems Research Center near Linneus, MO in March, 2005. Pasture selection was based on low to moderately low soil Bray I phosphorus analysis (Table 1). Pastures were organized into treatment groups, according to proximity for convenient pasture rotation. Annual fertilization treatments were 0 or 50 lbs P/acre (0-46-0), and 100 lbs N/acre (urea-N), and K (0-0-62), as recommended by soil test results. All pastures were supplied with salt blocks containing only NaCl. At least four replicated pastures were used for each treatment and pastures size averaged about 15 acres. We used 150 cow/calf pairs total in the experiment, therefore each replicate set of pastures had 25 cow/calf pairs. Calving of this herd began around February 15 and ended around March 15 each year. About 90% of the calves were siblings from the same red Angus bull (AI). Cows were preconditioned on the same large stockpiled tall fescue pasture for at least four weeks before being put on the treated pastures. On April 14, 2005 and on April 15, 2006, cows and calves were weighed and placed on appropriate pastures. Stocking rates were adjusted to produce similar grazing pressures on the various pastures. The amount of forage available was determined by using 50 different measurements with an Elinbank Rising Plate meter. The forage meter readings were calibrated with monthly forage harvests taken with a flail-type forage harvester. Using the forage harvester, we harvested, weighed and sub-sampled forage from ten 32" x 15' cuts from one pre-grazed pasture and one post-grazed pasture in each replicate set of pastures monthly. Sub-samples grabbed from each of the 10 harvested samples were pooled, dried, and stored for determination of quality components. The cows and calves were weighed monthly for four months during 2005, then the study was terminated because of drought conditions. Even though we had included extra pastures in the study, the severe dry weather resulted in almost no available forage for grazing by August. During 2006, there was adequate rainfall and plenty of grass for the entire season and the calves were weaned after about six and one-half months on the study.

Results:
The Forage Systems Research Center is an excellent site for this type of research. We were able to locate adequate numbers of low to moderate soil P pastures on the farm to accommodate this large scale study. This farm has a large cow herd and the genetics of the calves were top-notch, plus facilities were readily available for weighing the cows and calves frequently. Also, agronomists and animal scientists were extremely helpful in collecting forage samples, in rotating pastures and weighing the cattle. One difference between this study and the preliminary study that we conducted at the SW Center near Mt. Vernon was that cows calved earlier at FSRC, therefore calves went into the P study when they were over one month of age. At the SW Center, calves were actually born on or around the day the experiment began. The major problem with this study the first year was the lack of rainfall, which may have nullified the usefulness of the P fertilization, plus by July, soil test K levels were low in many of the pastures (Table 2). Soil test K levels are often low during drought since K is "fixed" in the clay. There were no P treatment differences in rate of gain or final weight of calves in 2005 (Tables 2 & 3). The 2006 calves on the +P pastures weighed 8 lbs more than calves from the -P pastures on 9-5-06 and 6 lbs more at termination on 9-20-06 (Table 5). The trends for calf weight gain in 2006 were consistently in favor of the +P pastures, but the difference in weight gain was not as great as expected based on our preliminary experiment at the SW Center.

Conclusions:
After a good summer of grazing, with good quality grass and great cattle, the calf weight response to P fertilization was positive but the 6lbs of final weight gain was not as great as expected. There could be at least two possible reasons for this, one is that calves were over one month of age before cow and calves were put on the treated pastures. The second reason could be that the low to moderate soil P levels in pastures were 20+ lbs/P acre (Bray I). Our studies at the SW Center were conducted on pastures that had only 7-8 lbs P/acre (Bray I). The 12+ lbs P/acre in the current study may be enough to maintain normal levels of calf weight gain by promoting adequate milk production by the cow.

Table 1. March 27, 2005 soil test data from pastures used in the phosphorus cow/calf study at the Forage Systems Research Center. Each value is the mean of data from all of the pastures within a particular treatment group, usually at least four different pastures.

Table 2. July 27, 2005 soil test data from the pastures used in the phosphorus cow/calf study at the Forage Systems Research Center. Note that soil K levels are markedly lower in most of the pastures as a result of the drought. Each value is the mean of data from all of the pastures within a particle treatment group, usually at least four different pastures.

Table 3. The 2005 calf performance on high and low phosphorus pastures at the Forage Systems Research Center. Start weight was on April 14, Period 1 weight was on May 12, Period 2 was on June 9, Period 3 was on July 5, and Period 4 weights were taken on August 9 and again on August 10. At the end of the experiment, the calves and cows were weighed on two consecutive days. Values are means of weight from 75 calves in the treatment.

Table 4. 2005 cow performance on high and low phosphorus pastures at the Forage Systems Research Center. Periods 1, 2, 3 and 4 are the same as those described in the legend of Figure 3. Values are means of weight from 75 cow in the treatment.

Table 5. Cow and calf weight gain and average daily gains for summer of 2006.