The Impact of a Kānuka Silvopastoral System on Surface Runoff and Sediment and Nutrient Losses in New Zealand Hill Country

47 Pages Posted: 6 Jan 2022

Abstract

New Zealand hill country is a pastoral region that has high levels of surface runoff and sediment and nutrient losses. Silvopastoralism has potential to mitigate these losses via the interaction of trees with the soil, pasture and livestock. This study compares surface runoff and sediment and nutrient losses (nitrogen and phosphorus) in pasture plots with and without Kunzea robusta de Lange et Toelken (kānuka) trees and investigates the reasons for the variation in these losses between kānuka pasture and open pasture. Annual surface runoff was 53.80 mm in kānuka pasture and 7.54 mm in open pasture despite kānuka pasture having improved soil conditions (in terms of porosity, organic matter and soil fertility). Kānuka pasture had species indicative of good pasture condition even though the plots had significantly less standing grass biomass. This was most likely due to livestock preferentially grazing the pasture under kānuka which led to less attenuation of surface runoff. Sediment and nutrient losses were 10 to 100 times greater in kānuka pasture, mainly due to the increase in surface runoff, but also because of livestock concentrating nutrients under the trees through excreta deposition. These results are contrary to past silvopastoral research and highlights that an extreme choice between shaded areas of good pasture condition and un-shaded areas of poor pasture condition within a pastoral hill side can lead to negative consequences in terms of surface runoff and contaminant losses because of livestock interactions. More research is required to understand these processes in other hill country farms and grazing conditions, and explore mitigation options.

Keywords: pasture condition, soil erosion, soil conservation, agroforestry, tree effects, ecosystem services

Suggested Citation

Mackay-Smith, Thomas H. and Burkitt, Lucy L. and López, Ignacio F. and Reid, Janet I., The Impact of a Kānuka Silvopastoral System on Surface Runoff and Sediment and Nutrient Losses in New Zealand Hill Country. Available at SSRN: https://ssrn.com/abstract=4002314 or http://dx.doi.org/10.2139/ssrn.4002314

Thomas H. Mackay-Smith (Contact Author)

Massey University ( email )

Private Bag 11 222
Palmerston North, 4442
New Zealand

Lucy L. Burkitt

Massey University ( email )

Private Bag 11 222
Palmerston North, 4442
New Zealand

Ignacio F. López

Massey University ( email )

Private Bag 11 222
Palmerston North, 4442
New Zealand

Janet I. Reid

Massey University ( email )

Private Bag 11 222
Palmerston North, 4442
New Zealand

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