Effect of grazing management and season on nitrogen and phosphorus content of leaves and stolons of white clover in mixed swards

Abstract

The nitrogen (N) and phosphorus (P) contents of leaf, surface stolon, and buried stolon of white clover (Trifolium repens L.) were measured in samples taken every 2 months, from pasture under rotational grazing by cattle (RGC) and set stocking by sheep (SSS), for 3 years. The effect of the system of grazing management of sheep on N and P content of 3 herbage classes of white clover was examined during a 1-year period by analysing samples taken monthly from pastures with 3 different management backgrounds; set stocked (SS), rotationally grazed (RS) or set stocked from lambing to drafting, then rotationally grazed for the rest of the year (CS). In the 3-year study, the content of N did not differ between the RGC and SSS treatments but the mean values of 4.59% in leaf, 2.75% in surface stolon, and 2.22% in buried stolon all differed. However, P contents differed between treatments: with RGC treatment, mean P levels decreased (0.43, 0.29, and 0.23% for leaf, surface stolon, and buried stolon respectively) whereas, with SSS treatment, contents in each of the respective herbage classes were higher and differences among the herbage classes were much smaller, the only significant difference occurring with buried stolon (0.51, 0.51, and 0.47% for leaf, surface stolon, and buried stolon respectively). The system of sheep grazing management affected both N and P contents in the same manner, with contents decreasing in the order SS > CS > RS. Again, there was a marked decrease in mean N content of the herbage classes in the order leaf (4.35%), surface stolon (2.97%), and buried stolon (2.11%), whereas the mean P contents of the herbage classes differed much less, with buried stolon (0.43%) being lower than leaf and surface stolon (both 0.51%). Seasonal variation in both N and P content of each of the herbage classes in both studies followed the same trend — higher values during the moist, cooler part of the year (May–September) and lower values during the drier, warmer period (January–March).

Keywords:

• white clover
• Trifolium repens
• N
• P
• stolon
• leaf
• petiole
• grassland management
• grazing systems
• seasonal variation
• pastures