Implications of Long‐Term Land Application of Poultry Litter on Tall Fescue Pastures

Abstract

Alabama's poultry industry is most heavily concentrated in the Sand Mountain region of northern Alabama. Disposal of litter (manure and bedding material) generated from poultry production in the region is typically accomplished by land‐spreading onto tall fescue ( Festuca arundinacea Schreb.) pastures. We conducted a study in four major poultry producing counties in the Sand Mountain region to determine the effects of long‐term litter use on soil and plant conditions related to pasture production and forage quality. Soil samples from 0 to 6 in. depth and plant tissue samples were collected from tall fescue pastures receiving annual applications of litter for 15 to 28 yr (littered) or not receiving such applications (nonlittered). These samples were analyzed for soil pH and organic matter, plant nitrate‐N, soil and plant total N, and extractable P, K, Ca, Mg, Cu, Fe, Mn, and Zn. Results point to higher soil pH, soil organic matter, and total N in soils receiving long‐term litter applications. Extractable soil P, K, Ca, Mg, Cu, and Zn were higher in littered than in nonlittered pastures. Tissue analysis showed that litter applications increased forage concentrations of N, nitrate‐N, P, K, Ca, Mg, Fe, and Cu as compared with forage from nonlittered pastures. The ratio K/(Ca + Mg) in plant tissue, associated with grass tetany potential, was higher in littered than in nonlittered pastures, but did not exceed the commonly accepted threshold value of 2.2. Our findings indicate that long‐term poultry litter application to tall fescue pastures has caused an accumulation of nutrients in soils and plants, but there was no evidence that this accumulation has created a forage quality problem. Research Question Alabama's large poultry industry generates enormous amounts of waste or litter (manure and bedding material) that is typically disposed of by spreading onto tall fescue pastures. Although use of poultry litter as a fertilizer for pasture can provide yields comparable to commercial fertilizers, long‐term use at heavy application rates may reduce pasture productivity through an oversupply of nutrients. The objective of this research was to determine the effect of long‐term land application of poultry litter on soil and plant tissue elemental concentrations of tall fescue pastures, and the implications for pasture productivity in the Sand Mountain region of north Alabama. Literature Summary Pasture productivity is determined by the level of sustainable animal production, and is affected by plant species, soil fertility, and animal management. Animal health problems owing to grazing of tall fescue heavily fertilized with poultry litter have been reported in the agronomic and animal science literature. The most frequently noted litter use problems are bovine fat necrosis and nitrate toxicity, which are associated with high levels of N use, and grass tetany, which has been related to heavy land‐application of potassium. Few studies, however, have investigated on‐farm soil and plant conditions related to pasture productivity following long‐term land applications of poultry litter. Study Description Soil samples 0 to 6 in. in depth and tall fescue tissue samples were collected from pastures in four counties in the Sand Mountain region of north Alabama. Locations: Littered and nonlittered pairs of pastures in Blount, Cullman, DeKalb, and Marshall Counties. Treatments: Long‐term littered (15 to 28 yr) and nonlittered pairs of pastures on matching soil series; three pairs per county for a total of 12 littered/nonlittered pairs of pastures. Analysis: Soil pH, percentage soil organic matter, plant nitrate‐N; plant and soil total N, extractable P, K, Mg, Mn, Cu, and Zn. Applied Question Does long‐term land application of poultry litter affect tall fescue pasture productivity? Long‐term litter application can provide benefits to the soil fertility status of tall fescue pastures such as higher soil pH and organic matter as compared with nonlittered soils (Table ). However, greater levels of soil and plant tissue total N in littered pastures may indicate a potential for raising forage N concentrations to levels that reduce animal productivity. Also, there is a potential for degradation of surface waters that receive runoff from long‐term littered pastures due to the large quantities of accumulated P in surface soils (Table ). With the exception of plant tissue concentrations of Mn and Zn, all other analyzed elements were higher in littered than in nonlittered tall fescue pastures (Table ). Because poultry litter contains a wide range of plant nutrients, consideration should be given to elements other than N, especially P. There was no evidence however, that elemental accumulations in soils and plant tissues had, in general, reduced pasture productivity or posed a significant threat to animal health. Recommendation Land‐application of poultry litter to tall fescue pastures is a practical and suitable means of poultry waste management, but application rates should not exceed plant or animal nutrient requirements. Average soil pH, soil organic matter, soil and plant elemental concentrations and plant K/(Ca + Mg) from littered and nonlittered pastures in the Sand Mountain region of Alabama. Soil Plant Littered Nonlittered Littered Nonlittered Variable pasture pasture pasture pasture pH 6.3 5.8 ‐‐ ‐‐ Organic matter,% 2.36 1.84 ‐‐ ‐‐ Total N, % 0.15 0.10 3.04 2.20 Nitrate‐N, ppm ‐‐ ‐‐ 394 170 P 227 31 0.39 0.20 K 144 54 1.65 0.84 Ca 1225 427 0.51 0.40 Mg 113 63 0.19 0.15 Cu, ppm 2.6 0.7 22 15 Fe, ppm ‐‐ ‐‐ 1620 854 Mn, ppm ‐‐ ‐‐ 149 248 Zn, ppm 10.0 2.7 45 42 K/(Ca + Mg) ‐‐ ‐‐ 1.07 0.68 Soil concentrations = ppm; plant concentrations = percentage on dry matter basis. K, Ca, and Mg in milliequivalents. A value of 2.2 for this ratio is associated with a potential for grass tetany.