Date of Award

2013

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Interdepartmental Program

First Advisor

José A. Amador

Abstract

Historically, much of the New England landscape was converted to pasture for grazing animals and harvesting hay. Today, consumer demand for local, sustainably produced food, the number of livestock farms and the land area used for farming are increasing in Rhode Island. In order to make sound management decisions, it is important to characterize the effects of livestock on the quality of pasture soils. Although pastures remain a fairly common part of the New England landscape, little research has been published on the effects of grazing animals on pasture soil quality. To assess this, I examined soil quality in farms raising beef cattle, sheep, and horses, using hayed pastures as a control. All pastures were situated on ablation till. Three pastures per livestock type and three control hayed pastures were sampled in May, August and October 2012. I interviewed farmers about their management practices, made soil profile descriptions to a 50-cm depth, and characterized vegetation species. I established a 10 m × 10 m sampling area in each pasture and assessed soil quality based on measurement of physical (aggregate stability, bulk density, soil organic matter, infiltration, soil structure, texture and penetration resistance), chemical (soil pH, electrical conductivity, extractable N and P) and biological (active C, earthworm numbers, soil respiration) parameters, according to general agricultural recommendations in the Cornell Soil Health Training Assessment Manual. The effects of livestock type and sampling date on soil quality parameters were analyzed using a one-way ANOVA on ranks. Penetration resistance, bulk density, aggregate stability, organic matter content and extractable phosphate differed significantly (P<0.05) among pasture type. Hay and sheep pastures had significantly lower penetration resistance and bulk density than horse or beef pastures, whose values were in the ideal range for bulk density, but in the acceptable and problematic ranges for surface penetration resistance, according to general agricultural recommendations. For aggregate stability, hay pastures had the highest fraction of water-stable aggregates, followed by sheep and beef pastures, though all values for all pastures fell within the ideal range for agricultural soils. Horse and hay farms had significantly lower extractable phosphate concentrations than beef or sheep farms, with approximately 25% of horse pasture values within the problematic ranges for soil phosphate, according to agricultural soil guidelines. The remaining soil quality parameters (active C, vegetation, electrical conductivity, pH, extractable N, infiltration rate, and earthworm numbers) did not vary significantly among pasture types or season. Soil pH and extractable NO3- values were problematic in all pasture types, whereas values for surface penetration resistance, active carbon levels, vegetation and earthworm counts were problematic in beef and horse pastures. Extractable PO43- was problematic in all pastures except hay. Penetration resistance and bulk density values were inversely correlated with organic matter content, aggregate stability and earthworm counts, whereas soil respiration was correlated with temperatures and soil moisture.

Overall mean soil quality values, calculated by converting values for each parameter to a % score and calculating the mean % score, were highest for hayed pastures (78), followed by sheep (74), with horse pastures having the lowest soil quality score (69), which was similar to that for beef pasture (70). Pasture soils generally sustain the greatest damage from traffic during wet conditions, which may explain why soil quality was lower in continuously grazed pastures, regardless of soil moisture conditions, whereas hay is generally harvested in warmer months when soil and vegetation are fairly dry. In addition, sheep are smaller than either horse or beef cattle, and exert less pressure per hoof print, which may lead to better soil quality in pasture. Soil quality could be improved in all pastures by liming soil, preventing traffic during wet soil conditions, and preventing overgrazing by rotating animals off pasture when vegetation height is reduced to 7-12 cm. By implementing these practices, farmers can address a variety of physical, biological and chemical soil quality issues, ultimately leading to better pasture production, which could lower animal feed costs considerably.

The results of my study provide baseline data on the effect different types of livestock have on pasture soil quality in Rhode Island, which may be useful in making sound land use and agricultural management decisions.

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