Conditions that favor clover establishment in permanent grass swards

Over seeding clover into permanent grasslands has many benefits, but successful establishment can be difficult as it depends on multiple interacting variables. This paper reports on a 2-year factorial experiment conducted to evaluate how the interaction of several variables: (i) height of residual grass stubble at sowing, (ii) defoliation frequency, and (iii) fertilization with P and K affected clover seedling emergence and subsequent biomass in a permanent grass sward. In 2010, a red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) mix was broadcast seeded into grass plots arranged in a split-split plot arrangement of treatments. Clover seed sown into short grass stubble produced two times more seedlings (226m(-2)) compared with sowing into tall swards (106m(-2)). Frequent defoliation facilitated clover establishment, but only when seed had been sown into short grass stubble. Fertilization increased red clover yield in year 1, but this also depended on interactions with defoliation frequency and stubble height. Overall, red clover benefitted from fertilization with P and K but only during the establishing year. Fertilization also promoted a less desirable weedy species, hop clover (Trifolium campestre Schreb.), which may have had negative impacts on clover yield and white clover persistence in year 2. The results highlight the complexity of managing grass-legume mixtures especially with respect to fertilization.