Response of Drainage Water Quality to Fertilizer Applications on a Switchgrass Intercropped Coastal Pine Forest

Augustine Muwamba,Timothy Callahan,Mohamed A Youssef,Jamie E Nettles,Ernest W Tollner,George M Chescheir,Timothy Appelboom,Devendra M Amatya,Hebert Ssegane,Francois Birgand

doi:10.3390/w12051265

Abstract

The objectives of this study were (1) to test the hypothesis that fertilizer applications do not increase nutrient fluxes on a switchgrass/pine forest (IC) when compared to a mature pine forest (MP) and (2) to evaluate post-fertilization (post-fert, 2014–2016) fluxes of nitrogen (N) and phosphorus (P) on IC and compare them to those observed during switchgrass growth prior to fertilization (pre-fert, 2012–2014) and site preparation for switchgrass establishment (site prep, 2009–2012). Nitrogen and P were applied to IC, a paired pure switchgrass site (SG), and MP, each about 25 ha in size, in June 2014, and again in June 2015 for the IC and SG sites only. Nitrogen and P concentrations were measured biweekly and rainfall and drainage outflow were measured continuously. During post-fert, the mean N concentrations and total loads were lower (p < 0.05) in IC than in SG and MP. The mean NO3-N concentration and loads in IC were lower during post-fert than during site prep. The post-fert phosphate concentrations in IC were lower than they were during pre-fert and site prep. Frequent N and P applications in IC did not significantly (α = 0.05) increase N and P fluxes, likely due to plant uptake and sorption on the acidic site.

Highlights

Traditional loblolly pine (Pinus taeda) forest management requires infrequent nitrogen (N) and phosphorus (P) applications, preferably two to three times during a 25 to 30 year growth cycle [1], unlike a switchgrass (Panicum virgatum L.)/pine system, which requires annual N and P fertilizer applications to maximize production [2]
We hypothesized that frequent fertilizer application in switchgrass/pine forest does not lead to significant differences in water N and P concentrations and loads compared to traditionally managed pure switchgrass and/or mature pine forest sites
Fertilizer application did not increase the nutrient concentrations and loads on the switchgrass intercropped (IC) treatment when compared to the mature pine (MP) forest, except for the phosphate loads

Summary

Introduction

Traditional loblolly pine (Pinus taeda) forest management requires infrequent nitrogen (N) and phosphorus (P) applications, preferably two to three times during a 25 to 30 year growth cycle [1], unlike a switchgrass (Panicum virgatum L.)/pine system, which requires annual N and P fertilizer applications to maximize production [2]. Water 2020, 12, 1265 have documented the effects of fertilizer application in pure switchgrass sites and forests with natural understory on plant growth, soil properties, and water quality and quantity. Greater N and P fluxes for a 10-year fertilized loblolly pine stand were observed when compared to a non-fertilized forest in Scotland County, NC [3]. The greater short-lived drainage water N concentrations of a pine-forested watershed in Carteret County, NC were attributed to N fertilizer application followed by three consecutive storm events right after fertilization [1]. We hypothesized that frequent fertilizer application in switchgrass/pine forest does not lead to significant differences in water N and P concentrations and loads compared to traditionally managed pure switchgrass and/or mature pine forest sites

Objectives

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Results

Conclusion