Refining foliage sampling protocols for white clover

Abstract

White clover (Trifolium repens) foliar ‘grab’ samples were taken pre-grazing from two irrigated experiments at Lincoln University at ~6 week intervals from August 2019 to May 2021. Clover leaves were divided into lamina and petiole before analysis. The results for nitrogen (N), phosphorous (P), potassium (K) and sulphur (S) foliar concentrations are reported.
 While there were seasonal variations, N% and S% were consistently higher in the white clover lamina than the petiole, K% was mostly higher in the petiole, and P% was higher in the lamina during the winter/early spring period. With increasing clover sward height, the lamina to petiole DW ratio declined from 4, at a sward height of 5 cm, to 1 at 20 cm. The lamina+petiole sample had lower concentrations of N and S than lamina alone. Over time, foliar N% was relatively stable but concentrations of P, K and S showed ~ two-fold variation and may have been affected by low soil moisture.
 The diagnosis of clover nutrient status should be based on lamina-only samples taken during spring, when plant growth is fastest, and just prior to grazing when there is sufficient herbage. Clover foliage sampling should routinely be used to inform fertiliser recommendations rather than relying on the development of visual symptoms of nutrient deficiency.