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)

Effect of Boron and Nitrogen Application on Seed Production of Lotus uliginsus

Four rates or boron (B) and 2 rates of nitrogen (N) were applied to a mature stand of lotus 11ligi11os11s Schk. cv. Grasslands Maku before flowering, on 10 November 1988. The 2 rntes of N (40 and 80 kg N/ ha) were either applied once or applied at 5 and 10 kg N/ha respectively, at weekly intervals for 8 weeks. N did not increase seed yields. Weekly applications of N significantly (P\u3c0.05) decreased seed yields by 28%. B at 0.91 kg/ha increased seed yields by 7% but this increase was not significant. While seed yields in some tropical legumes may benefit from N application, Grasslands Maku does not benefit. Rather, seed yields are depressed. The application of B did not significantly change seed yields, but more research on B may be needed in areas where B availability is thought to be low

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