COLLECTION, CHARACTERIZATION, PRESERVATION, AND EXCHANGE OF RHIZOBIA STRAINS FOR SUBTROPICAL LEGUME FORAGE DEVELOPMENT IN URUGUAY AND THE US
Title: Long term effect of higher soil penetrometer resistance in cow congregation zone: Implication on soils and forage quality
Submitted to: Agronomy for Sustainable Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 25, 2009
Publication Date: July 10, 2009
Citation: Sigua, G.C., Coleman, S.W. 2009. Long-term effect of cow congregation zone on soil penetrometer resistance: Implication on soils and forage quality. Agronomy for Sustainable Development Journal. 29:517-523.
Interpretive Summary: Grazing, trampling, and dung deposition by large herbivores often result in a zone of impact on many vegetation and soil parameters including vegetation basal cover, soil bulk density, and soil penetrometer resistance. Higher degree of soil penetrometer resistance can reduce crop yields and can lead to water and soil quality degradation due to increased runoff and soil structure destruction. The effect of trampling appears to be less severe on vegetated grasslands than on poor or bare soil. We question whether cattle congregation sites are more compacted than in other pasture locations. Cattle congregation sites typical on most forage-based cow-calf ranches, such as mineral feeders, water troughs and shaded areas were evaluated for compaction by measuring soil penetrometer resistance. Cattle grazing and trampling near the center (0.9 to 1.7 m) of cattle congregation sites reduced the density of grass cover, and increased soil bulk density. Areas around the cattle congregation sites may have reduced soil aggregate stability as the surface becomes crusted, and may be correlated to bare soil and higher soil bulk density. Drier soils at the mineral feeders and water troughs tended to be harder and more compacted than moist soils in Shady sites. Soil penetrometer resistance decreased linearly out from the center of mineral feeders and water troughs. These soil penetrometer resistance values were in the “fair” range of root penetration. Penetrometer resistance of soils can be a good predictor of root system performance and especially useful in predicting root extension into the deeper regions of the root zone at the congregation and grazing zone in pasture.
Higher degree of soil penetrometer resistance (SPR) can reduce crop yields and can lead to water and soil quality degradation due to increased runoff and soil structure destruction. The effect of trampling appears to be less severe on vegetated grasslands than on poor or bare soil. Understanding cattle movement in pasture situations is critical to understanding their impact on agro-ecosystems. Movement of free-ranging cattle varies due to spatial arrangement of forage resources within pastures and the proximity of mineral feeders (MF), water troughs (WT), and shades (SA) to grazing sites. We hypothesized that cattle congregation sites (CCS) are more compacted than in other pasture locations. The objective of this study was to test whether soils at cattle congregation sites typical on most forage-based cow-calf ranches, such as MF, WT, and SA are more compacted and have greater SPR than in other pasture locations under Florida conditions. Penetrometer readings were collected from two soil depths (0-20 and 20-40 cm) at different locations around the CCS following a radial (every 90 degrees: North, South, East, and West direction) sampling pattern at 0.9, 1.7, 3.3, 6.7, 13.3, 26.7, and 53.3 m away from the approximate center of MF, WT, and SA. Soil penetrometer resistance varied significantly with CCS (p=0.001); distance from the center of CCS (p=0.001); sampling depth (p=0.001); and the interaction of CCS and distance from center. Soil penetrometer resistance decreased linearly with distance away from the center of MF and WT. The least SPR in all years were observed from SA (1,200 x 103 Pa) while PR at WT was about 1,600 x 103 Pa and at MF of 1,800 x 103 Pa. These SPR values were in the “fair” range of root penetration. The cone penetrometer looks promising as a tool for predicting root system performance and best described by a quadratic equation: Root Penetration (%) = 153.1 + 4.8x2 -55.2x; R2 = 0.98**; x is the SPR reading in soils.