Impact of Cattle Grazing in South Florida Pat Hogue, CED/Livestock Okeechobee County December 2010 Article of the Month And I will seed grass in thy fields for cattle, that thou mayest eat and be full – Deuteronomy 11‐15 He causeth the grass to grow for the cattle, and herb for the service of man; that he may bring forth food out of the earth – Psalms 104‐14 When I think of the regulatory atmosphere imposed on the beef cattle industry, and agriculture in general in South Florida, particularly in regards to water quality, I get reminded of my major professor in my graduate work in college, and how he always started his pasture and forage management courses each year with quotes from the Bible that pointed out the purpose for which cattle were put on this earth. That purpose, according to numerous quotations, was to consume the grasses and herbs man cannot effectively utilize, and convert it to usefulness for man as food or service. We know that Florida has the oldest history of cattle grazing and production in the United States. Cattle were first introduced in the US, in Florida when they were brought from Spain by Juan Ponce De Leon and his crew in 1521, and later introductions came with Hernando DeSoto in the 1530’s. Prior to that time there would have been no impact on the waters of Florida by cattle grazing, other than the periodic impact bison may have had as they ventured to the state periodically in their nomadic roaming of the states. However, we do not know, and could only hazard any guess, as to what the nutrient or other particulate loads were prior to these times. We know that the Native American’s in Florida at the time, and later settlers took up cattle grazing and production that were the precursors to the modern Florida beef cattle industry, and that Florida, since those times, has always been a cattle grazing state, and one of the leaders in this endeavor throughout US history. What we also know is that even prior to cattle coming to Florida, that there were huge deposits of phosphorus in the ground that later became a leading mining industry for the state, and Florida is one of the leading suppliers of phosphorus fertilizers not only to the US, but the rest of the agriculture producing world. Did these phosphorus deposits have any effect on waterways in Florida even prior to cattle coming to the state and before we mined it and produced huge quantities of fertilizers applied to the soils? Again, we have no empirical data to prove this, yet there is evidence that the soils in South Florida are probably inherently high in phosphorus, and may have been even before man started using the nutrient as a means to increase agricultural production. It’s reasonable to assume, and a case could probably be made that with all the water raining down on and flowing through and interacting with all the land that may contain high phosphorus levels South Florida, water bodies such as Lake Okeechobee may have always contained large amounts of the nutrient. The graph below is the total phosphorus load in to Lake Okeechobee as kept by South Florida Water Management District since 1973. The blue‐green line bear the bottom of the graph represents the 150 metric ton goal that regulation has been trying to attain. The blue line, with all the peaks and valleys is the actual annual load, and the yellow line is a calculated five year annual rolling average load. Annual Average
Five-Year Rolling Average
Goal
1000
900
TP Load
(mt per yr)
800
700
600
500
400
300
200
100
0
Year
As you digest this information you can see that only four times since 1973, has the P load dropped significantly below the 300 metric ton annual load mark, and the last, in 2006‐
2007 should remind us that those four times were drought periods where little water, relatively speaking, was flowing. And again, when looking at the spikes, and remembering 2004‐2005, these were very wet periods where a lot of water was flowing. As we continue to look at this graph, a couple of other things we need reminding of is that since the mid to late 1980’s, the number of dairy’s and dairy cattle has been reduced significantly from previous years, and the dairy industry has undertaken some rigorous water retention and P abatement programs and structures to reduce their effect on water quality. We also must remember that since the early 1990’s there has been a greatly reduced amount of phosphorus applied to pastures in South Florida as a result of research studies that showed it wasn’t needed as often an in amounts previously applied. In the past, and over the past several years, numerous research projects have undertaken the task of trying to determine the effect cattle grazing has had on water quality in South Florida, and a few of those are summarized here. One of the largest scale and most significant was a project undertaken at Buck Island Ranch by John Capece, Kenneth Campbell, Patrick Bohlen, Donald Graetz, and Kenneth Portier under the auspices of South Florida Water Management District, IFAS, and Florida Cattlemen’s Association. This was a large scale research pasture project on 420 ha (1038 acres) with 8 improved summer pastures, and 8 semi‐improved winter pastures with 4 stocking rates, no cattle, low, medium, and high conducted for 5 years, 1998‐2003, as indicated in their Table 1 below. This research project was designed to investigate the influence of beef cattle stocking rate on nutrient loads in surface water runoff. Their results, as indicated in their Table 3 below, do not show that increasing stocking rates would increase nutrient loads, therefore reducing stocking rate would not be effective BMP for reducing non‐point source pollution. In fact results indicate removing cattle from a grazing system resulted in higher nutrient loads than even the most intense stocking rate, practices directed at reducing nutrient inputs might be more effective at reducing loads than removing cattle from a grazing system. Gilbert Siqua, Mary Williams, and Samuel Coleman undertook a long term study, 1988 – 2000, to investigate the long term effect of pasture management (grazing + haying) on soil P dynamics (levels and changes) in subtropical beef cattle pastures with bahiagrass and rizhoma peanut, with, or without P fertilization. In the process they looked at fertilization of the studied grazing and haying areas at the STARS Brooksville Main Station and Turnley Unit going back to 1983 and previously based on IFAS soil test results recommendations. Their findings indicated that environmentally, soil P levels in STARS pastures are declining. During the 12 year study, there was no P build up in STARS pastures despite the annual application of P, and in‐field daily loading of animal waste. They further found that levels and changes of soil P at STARS from 1988 to 2000 were responsive and sensitive to P fertilization. Gilbert Siqua, Robert Hubbard, Samuel Coleman followed this up with a 3 year study (2004‐2006) looking at soil, plant, surface and shallow ground water P on a sloped pasture that was part of a rotational grazing system. This study was done under the hypothesis that properly managed cow‐calf operations in subtropical agroecosystem would not be a major contributor to excess loads of P in surface and ground water. Their Figure 1 below shows a picture of the site with soil and plant sampling sites located as well as monitoring wells, and should be noted that this site was part of a larger rotational grazing system. Their Table 1 below shows a compilation of the grazing activity as cattle grazed through this particular portion of the grazing system including days grazed, number of animals and units per acre, manure excreted and phosphorus in manure. Their Figure 3, below, shows the average concentration of P in ground water at the various slope locations and at the seep at the bottom of the slope. From this research, they concluded that current pasture management including cattle rotation in terms of grazing days and current fertilizer (inorganic+manures+urine) application rates for bahiagrass offer little potential for negatively impacting the environment. Further that properly managed livestock operations contribute negligible loads of total P to shallow groundwater and surface water, overall, there was no buildup of total P in bahiagrass based pastures. More recently, A.K Obour, M.L. Silveira, J.M. Vendramini, L.E. Sollenberger, G.A. O’Connor, and J.W. Jawitz evaluated effects of revised N and P fertilizer recommendations on forage yield and nutritive value and potential effects on water quality in bahiagrass on a Spodosol. They utilized these treatments, three N rates (0, 56 and 112 kg N/ha) and four P rates (0, 5, 10, and 20 kg P/ha) in this two year study in an established bahiagrass pasture and reached the following conclusions: ‐Bahiagrass yields response to P depends on environmental conditions and can vary from year to year ‐Tissue P and P uptake are affected by P application rates, but had no effect on CP concentrations ‐Mehlich‐1 extractable P in Ap, E, and Bh horizons are not affected by P application rate ‐P application had no effect on leachate P concentration ‐Results showed P fertilization at agronomic rates to low input bahiagrass systems has no environmental impacts on water quality These and numerous other research projects over the years would seem to indicate that cattle grazing in South Florida have little to no adverse affects on water quality, particularly in regard to phosphorus, and some to nitrogen. So you may have to judge for yourself as will others if cattle grazing is an environmental detriment, but don’t overlook that the environment itself may be a major contributor. Three major studies of bulk rainfall, 1976‐77, 1993‐2001, and the third a rainfall and dryfall study, have shown that bulk annual rainfall are above permissible rates for shallow lakes for P loading, with the earliest also indicating the same for N loading. The rainfall/dryfall study also indicated the annual P collected in air dryfall on an annual basis, was more than three times that of rainfall. Soil samplings done of the Kissimmee River spoil bank on a periodic basis from 1998 through 2009 have shown that phosphorus levels in this soil material ranges from 120+ to 448+ parts per million phosphorus. The + indicates that at that point testing further is irrelevant. This soil material was taken directly from the canal that is currently the Kissimmee river and is either piled along its banks, or has been utilized as road bed or other fill type materials in the basin, but runoff from it ends up in either the Kissimmee river or other tributaries draining to Lake Okeechobee. This is only some of the evidence that possibly we have inherently high phosphorus levels in the soils in South Florida. In his travel notes of his explorations of South Florida, when he encountered a massive body of water which is believed to have been Lake Okeechobee, Hernando DeSoto wrote that the water was muddy and murky and had a bad smell to it and he believed it was unfit to drink. So after almost 500 years has cattle grazing had a significant effect on water quality in South Florida, or are there other considerations that must be accounted for like the environment itself, and perhaps the overwhelming population growth in the area?