105 Botanical composition, yield, horse preference, and forage and soil nutrient values of grass pastures treated with different soil amendments

Abstract

Forage is the foundation of a horse's diet, therefore, pasture management is critical to improve horse health and pasture productivity. The objective of this study was to evaluate botanical composition, horse preference, yield, and forage and soil nutrient values of pasture treated with horse manure, horse compost, commercial urea fertilizer, and a no amendment control. Researchers hypothesized soil amendments would increase soil nutrients and yield with minimal effects on botanical composition, preference and forage nutrient value. Replicated (n = 3) plots of established cool-season mixed grass pasture were 3 × 6 m and located in St. Paul, Minnesota. The soil was a Waukegan silt loam with a pH of 6.4 and 47 g kg–1 organic matter. Urea was applied based on initial soil test recommendations, 0.64 cm of compost was applied based on common recommendations, and manure was applied at a rate to represent horse manure deposition in May 2022. Sample collection and grazing periods occurred in May, June, July, August, and October 2022, each over a 2-d period. Botanical composition, average forage height and maturity, soil samples, forage samples, and forage yield were taken immediately before grazing. Horses were allowed to graze all plots for 4 h with preference visuallyassessed at 2- and 4 h post-grazing based on percent removal. Data were analyzed as a randomized complete block design using PROC MIXED in SAS with significance set at P ≤ 0.05. Season-long yield ranged from 2,690 to 3,363 kg DM ha-1 and did not differ across treatments (P > 0.05). Botanical composition differed across treatments with the control having the most weeds (32%) and the least amount of grass (62%) while manure treatments resulted in the most bare ground (11%; P ≤ 0.05). The soil nutrients magnesium and phosphate were highest in compost-treated plots and nitrate-nitrogen and sodium were highest in manure-treated plots (P ≤ 0.05). Forage nutrient content did not differ across treatments (P > 0.05). Horses did not prefer pasture treated with manure and only 15 and 33% of forage was consumed after 2 and 4 h, respectively (P ≤ 0.001). All other treatments averaged 53 and 78% removal after 2 and 4 h, respectively. Based on differences observed in botanical composition and horse preference, commercial fertilizer and compost appear to be the most beneficial soil amendments for horse pastures.