Copper deficiency in lucerne (Medicago sativa. L.)

In the course of these studies more questions have been posed than answered. It is clear that Lucerne production is being limited by low Cu levels in some areas. The relationships between yield and plant composition were rather different from those predicted from other studies; it is considered that this indicated that the present understanding of these relationships is far from adequate. A survey of Cu content of Lucerne growing on Eyre, Lismore and Wakanui soils showed the first two to supply just enough Cu for healthy plant growth at most sites. Wakanui soils grew Lucerne with more than adequate Cu contents. Variation within stands was not great, bulk sampling should give adequate information about the Cu status of any particular stand. Variation due to season was not marked. It is concluded that herbage Cu levels on all soils surveyed were sufficiently low to cause concern about animal health and that it is reasonable to assume similar or lower Cu levels in the other “old” shallow soils of Canterbury

How far have we come: 75 years ‘in clover’?

We reflect on what has been a recurring theme in the history of agricultural research in NZ – the understanding that while we grow white clover for its capacity to fix nitrogen, this increase in fertility ultimately passes to benefit the accompanying grass. The association of clover and grass is regarded both as a wonderful harmony upon which our economy depends, but also as a competition between species that too often defeats our efforts to realise clover’s full potential. We review and revisit the nature of the interaction between the species, and we offer some radical approaches looking forward. These include simple pragmatic options for management for immediate gains in performance, and we identify the need for some critical rethinking to fundamentally alter how grass and clover interact.The study of grass/legume interaction by Schwinning & Parsons (1996a,b,c) was funded by the Biotechnology and Biological Sciences Research Council (UK) at the Institute for Grassland and Environmental Research, Devon, and its presentation in NZ by an AgResearch Senior Research Fellowship in 1995/6 at Grasslands, Palmerston North. We extend our thanks also the Universities of Melbourne (Victoria); Lincoln (NZ); and Imperial College (UK)

Warming prevents the elevated CO₂-induced reduction in available soil nitrogen in a temperate, perennial grassland

Rising atmospheric carbon dioxide concentration ([CO₂]) has the potential to stimulate ecosystem productivity and sink strength, reducing the effects of carbon (C) emissions on climate. In terrestrial ecosystems, increasing [CO₂] can reduce soil nitrogen (N) availability to plants, preventing the stimulation of ecosystem C assimilation; a process known as progressive N limitation. Using ion exchange membranes to assess the availability of dissolved organic N, ammonium and nitrate, we found that CO₂ enrichment in an Australian, temperate, perennial grassland did not increase plant productivity, but did reduce soil N availability, mostly by reducing nitrate availability. Importantly, the addition of 2 °C warming prevented this effect while warming without CO₂ enrichment did not significantly affect N availability. These findings indicate that warming could play an important role in the impact of [CO₂] on ecosystem N cycling, potentially overturning CO₂‐induced effects in some ecosystems