Tropical Grasslands (2003) Volume 37, 170–175

Defoliation of Paspalum atratum during the growing season affects tiller and plant density the following spring

R.S. KALMBACHER and F.G. MARTIN

University of Florida, Range Cattle Research and Education Centre, Ona, USA

Abstract

Atra paspalum (Paspalum atratum) in subtropical Florida has occasionally died in winter where it was lightly stocked or where pastures had been destocked for seed production. We studied tiller and plant density in the spring following 4 different April–November defoliation regimens on fertilised (168:15:141 kg/ha of N:P:K annually) or unfertilised grass. Total vegetative tiller density in November (2-year mean) was highest (166/m2) where plants were cut every 35 days from April–November (T1) compared with all other treatments (mean of 40/m2). In T1, the canopy was kept short and consisted entirely of dominant tillers that had been repeatedly cut. Where plants were cut every 35 days from April–mid-July followed by removing forage in November (T2), 33% of the tillers were sub-dominant, small tillers. Similarly, 46% of the tillers in plants cut every 35 days from April–mid-July followed by not cutting in November (T3) were sub-dominant tillers at the start of winter as were 63% of tillers in an uncut control (T4). The 1997–98 year was frost-free, but in January 1999, -3.3°C at the soil surface killed the exposed canopy. There was a fertiliser x cutting treatment x year interaction for tiller density in March. Where the canopy had not been cut in November (T3 & T4), year had a more profound effect on March tiller density than in T1 & T2. Mean tiller density in March was greater during the frost-free 1998 (232/m2) than in the colder 1999 (160/m2). The difference between years was especially great in T4 (166/m2 in 1998 vs 55/m2 in 1999). Fertilising in 1998 in T4 reduced tiller density in March 1999 (21 with vs 88/m2 without fertiliser). Plant density in March 1998 was lower in T4 (28/m2) than in all other treatments (mean of 49/m2). In March 1999, all treatments differed from one another, with 15 plants/m2 in T4 and 62/m2 in T1. In regions where frost occurs, atra paspalum should be regularly utilised to prevent a large build-up of foliage before winter, especially if heavily fertilised during summer.

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