Spatial soil nutrient-plant-herbivore linkages: A case study from two poultry litter amended pastures in Northwest Arkansas

Authors: BRADEN, INDI - Southeast Missouri State University; WEST, CHARLES - Texas Tech University; Ashworth, Amanda

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2018
Publication Date: 2/7/2019
Citation: Braden, I.S., West, C.P., Ashworth, A.J. 2019. Spatial soil nutrient-plant-herbivore linkages: A case study from two poultry litter amended pastures in Northwest Arkansas. Agrosystems, Geosciences & Environment. 2:180036. https://doi.org/10.2134/age2018.09.0039.
DOI: https://doi.org/10.2134/age2018.09.0039

Interpretive Summary: Poultry litter is commonly surface-applied on perennial pastures as a low-cost fertilizer to support forage growth in cow-calf operations. Surface applications expose litter to nutrient losses, which is difficult to predict due to differences in landscape conditions. In addition, long-term applications can result in excessive nutrient buildup relative to potential plant use, which can lead to reduced surface water quality. Therefore, researchers set out to describe spatial relationships of selected litter-amended pastures on two beef cow-calf farms in northwestern Arkansas. Fields were sampled for soil nutrients, vegetative composition, and cover using two sampling techniques. At both scales, relationships were found among soil nutrients, soil characteristics, and forage species composition. In addition, grazing strategies influenced nutrient excretion patterns spatially, which, in turn, affected the on-farm risk of nutrient loss. These results provide evidence of the influence of sampling technique on soil test impacts and development of best management practices for sustainable on-farm nutrient management.

Technical Abstract: Knowledge of phosphorus (P) movement and its transformation across pastoral landscapes based on species composition and soil properties is largely unknown. Detailed analysis of the soils, forages, and landscapes can aid in targeting management of poultry litter and forage practices in ways consistent with livestock production and water quality goals. Objectives were to describe spatial relationships of soil and plant characteristics in selected litter-amended pastures on two beef cow-calf farms in northwestern Arkansas. Fields were grid-sampled for soil nutrients, vegetative composition, and cover at two sampling scales (14 and 60 m) for correlation analyses. For both scales on Farm A, positive correlations were found among exchangeable K, Ca, and Mg with organic matter (OM). Correlations between pairs of soil variables were likely the result of accumulated litter-derived nutrients. Bermudagrass [Cynodon dactylon (L.) Pers.] cover was positively correlated with soil-test P, dissolved reactive P, and K for the 14-m sampling grid on Farm A, whereas tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] cover was negatively correlated with those soil variables. This contrast between grass species suggests that higher soil nutrient accumulations associated with poultry litter application favored bermudagrass growth. Overall, feeding and grazing strategies influence the amount and spatial pattern of nutrient excretion, which, in turn, affect the risk of nutrient loss and fertilizer requirements. These results provide evidence of the influence of grid sampling size on soil test impacts and interpolations for site management. Future GIS-based studies are needed to identify sampling frequency per terrain attributes for P index mapping.