Effects of Growing-Finishing Pig Stocking Rates on Bermudagrass Ground Cover and Soil Properties

Abstract

This study compares four stocking rates (37, 74, 111 and 148 pigs ha^-1) for growing to finishing pigs (18.4 ± 0.5 kg and 118.5 ± 2.0 kg and 35.7 ± 2.1 kg and 125.7 ± 2.3 kg initial and final BW for grazing periods 1 and 2, respectively) and their effect on ground cover and soil traits in bermudagrass (Cynodon dactylon [L.] Pers) pastures, over two 14-week grazing periods (July-September and May-August). The study was conducted at the Center for Environmental Farming systems at the Cherry Research Station, Goldsboro North Carolina. A continuous stocking method was implemented to manage the pasture. The percent ground cover was estimated with a modified step point technique. Soil samples were collected in three sampling positions (center, inner and outer areas of the paddocks) and two soil sampling depths (0-30 and 30-90 cm). The experimental design was a completely randomized block with three field replicates. Data were analyzed using the PROC GLIMMIX procedure of SAS/STAT ^® Version 9.4. Greater ground cover and lesser soil nutrient concentrations were registered in bermudagrass paddocks managed with 37 pigs ha^-1. The results of this study also validated the existence of a spatial pattern of soil properties, which differed among sampling positions and depths.

Keywords: bermudagrass; ground cover; nutrients distribution; outdoor pigs; pasture pigs; soil depth; soil nutrients; soil properties; soil sampling position; stocking rates.

Figure 1

Soil sampling positions. C: Center; I: Inner; O: Outer; Distances among sampling points were estimated using Pythagoras’ theorem [10].

Figure 2

Weekly precipitation and temperature during the experimental period. Source: State climate office of North Carolina, North Carolina State University. CRONOS/ECONet Database [12].

Figure 3

Vegetative ground cover (%) in bermudagrass paddocks grazed with pigs over two 14-week grazing periods. (a) Ground cover, (b) Living vegetation and (c) Vegetation residues. Data are the means of three field replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 3

Vegetative ground cover (%) in bermudagrass paddocks grazed with pigs over two 14-week grazing periods. (a) Ground cover, (b) Living vegetation and (c) Vegetation residues. Data are the means of three field replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 4

Effect of the interaction grazing period × stocking rate on the ground cover of bermudagrass paddocks at the end of the grazing periods. a–e: means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. The Letters display does not reflect all significant comparisons. The following additional pairs are significantly different: GP1 SR111 vs. GP2 SR111; GP1 SR148 vs. GP2 SR148; where GP: grazing period and SR: stocking rate. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 5

Effect of the interaction sampling position × sampling depth on soil bulk density (Mg m⁻³) of bermudagrass paddocks grazed with pigs during one grazing period. a, b: means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data correspond to the first grazing period and are the means of three field replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 6

Effects of the interaction grazing period × sampling depth on the concentrations (kg ha⁻¹) of (a) NO₃⁻-N, (b) NH₄⁺-N and (c) Total-N in soil samples from bermudagrass paddocks managed with different pig stocking rates for two 14-week grazing periods. a, b, c: means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three field replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 6

Effects of the interaction grazing period × sampling depth on the concentrations (kg ha⁻¹) of (a) NO₃⁻-N, (b) NH₄⁺-N and (c) Total-N in soil samples from bermudagrass paddocks managed with different pig stocking rates for two 14-week grazing periods. a, b, c: means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three field replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 7

Effects of the interaction grazing period × sampling depth on the concentrations (kg ha⁻¹) of (a) PO₄⁻-P and (b) Total-P in soil samples from bermudagrass paddocks managed with different pig stocking rates for two 14-week grazing periods. a, b, c: Means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 7

Effects of the interaction grazing period × sampling depth on the concentrations (kg ha⁻¹) of (a) PO₄⁻-P and (b) Total-P in soil samples from bermudagrass paddocks managed with different pig stocking rates for two 14-week grazing periods. a, b, c: Means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 8

Effect of the interaction stocking rate × sampling position on soil NO₃⁻-N (kg ha⁻¹) in bermudagrass paddocks grazed with pigs during two grazing periods. a, b, c: For each grazing period, means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three field replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 9

Effect of the interaction stocking rate × sampling depth on soil PO₄⁻-P (kg ha⁻¹) in bermudagrass paddocks grazed with pigs during two grazing periods. a, b, c: Means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. The Letter display does not reflect all significant comparisons. The following additional pairs are significantly different: SR148 SD30-90 vs. SR148 SD0-30; where SR: stocking rate and SD: sampling depth. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 10

Effect of the interaction sampling position × sampling depth on soil Total-N (kg ha⁻¹) in bermudagrass paddocks grazed with pigs during two grazing periods. a, b, c: Means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 11

Effect of the interaction sampling position × sampling depth on soil Total-P (kg ha⁻¹) in bermudagrass paddocks grazed with pigs during two grazing periods. a, b, c, d: Means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 12

Effect of the interaction grazing period × stocking rate × sampling depth on soil Total-N (kg ha⁻¹) in bermudagrass paddocks grazed with pigs during two grazing periods. a, b: means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. The Letter display does not reflect all significant comparisons. The following additional pairs are significantly different: GP2 SR148 SD0-30 vs. GP2 SR37 SD0-30; where GP: grazing period, SR: stocking rate and SD: sampling depth. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.

Figure 13

Effect of the interaction grazing period ×sampling position × sampling depth in soil Total-P (kg ha⁻¹) in bermudagrass paddocks grazed with pigs during two grazing periods. a, b, c, d: Means having the same letter are not significantly different at the 5% level of probability as indicated by the Multiple Comparisons test—simulate option. The Letter display does not reflect all significant comparisons. The following additional pairs are significantly different: GP1 SP-C SD0-30 vs. GP1 SP-C SD30-90; GP1 SP-I SD30-90 vs. GP1 SP-C SP30-90; GP1 SP-O SD30-90 vs. GP1 SP-C SD30-90; where GP: grazing period; SP: Sampling position, SP-C: center, SP-I: Inner, SP-O: Outer; SD: sampling depth. Data are the means of three replicates. Errors bars represent plus or minus one standard error of the means within the interaction.