Influence of phosphorus fertiliser use on two New Zealand pasture insect pest communities

Abstract

Phosphorus (P) fertilisers are an important management tool in modern agriculture, including the pastoral sector, to maximise pasture productivity. However, P-application can have significant environmental consequences while also affecting invertebrate biodiversity and abundance. To understand the effects of repeated P-fertiliser applications, we analysed three years of sampling of the pasture invertebrate pest fauna from two long-term P-fertiliser trials in New Zealand, one hill country (Ballantrae: 0, 375 kg SSP ha¯¹ annually) and the other in flat land (Winchmore: 0, 175 (Sechura), 188, 250, 375 kg SSP ha¯¹ annually). We aimed to determine whether P-applications affected the abundance and order richness of pasture insect pests and if these could be linked with pasture production and botanical composition. Order richness did not differ between the fertiliser treatments, but we detected a significant difference in invertebrate community composition as well as indications that P-fertiliser increases the total invertebrate pest abundance in flat land pastures. Most notably, clover root weevil (Sitona obsoletus) abundance increased in P-fertilised pastures, which may be positively correlated with increasing clover content, whereas grass grub (Costelytra giveni) abundance initially increased with P-fertiliser input but subsequently declined at higher application rates. Pasture production increased with P-fertiliser inputs. The study highlights the complex interactions between P-fertiliser application and pasture invertebrate communities, emphasising how strategic P-fertiliser management can influence pest dynamics in agricultural ecosystems. This underscores the need for balanced P-fertiliser management to optimise both pest control and pasture health.