Nitrogen or Water Limitation to Grassland Growth during a Moderate Dry Season in the Humid Tropics

The aim of this work was to compare the effects of nitrogen and water shortage on grassland production during a moderate dry season in a tropical humid environment. The results of two experiments carried out in Guadeloupe (FWI) have shown that during dry spells, the reduction in growth of natural grasslands based on Angleton grass (Dichantium aristatum) is more easily corrected by nitrogen fertiliser application than by irrigation. This shows that it is not the availability of water, but that of nitrogen, which is limiting the primary production of Angleton grass, stands. This result is less clear for a pasture based on Pangola grass (Digitaria decumbens), a species introduced to improve forage production. Research experience in the field of water-plant-weather relations in a humid or sub-humid tropical environment cannot be extrapolated to animal production systems based on natural grasslands. The productivity of this forage resource is much more dependant on nitrogen availability, during periods of low rainfall or when water soil reserve is low