IMPACT OF GRAZING ON BOTANICAL COMPOSITION OF NATURAL HERBAGE AND SOIL CHARACTERISTICS
A long term (6 year) grazing experiment was conducted in a coconut plantation atHakmana, a farming village in the southern Sri Lanka, to observe the impact ofgrazing on botanical composition of natural herbage and soil characteristics. Thetreatments were ungrazed coconut land (UO), continous grazing of naturalherbage under coconut with out straw (0), 0 + rice straw adlibitum (OS) and OS+ supplements (OSS), with a density of 3 anirnals/ha in all the treatments.
The changes in botanical composition at the end of the six-year period indicatedthat herbs were dominant in the UO treatment, with an increase of the productionof herbage with time, Euphatorium odoratun, Veronica cinera and Cyperuskyllingia were the most dominant species. The highest decrease in herbageproduction were seen in animals that were not given straw (0) and the declineworsened with time indicating overgrazing and soil erosion. In contrast the initialdecline in herbage yields gradually increased in OSS indicating a possibility of astocking rate greater than 3 animals/ha, considering the subjective observations ofthe ground cover in paddocks as well. Due to the changes in grazing pressure, thepercentage of prostate grass species (Axonopus compressus, axoopus aJJinis etc.)and leguminous species (Desmodium spp.) improved the ground cover in OSthrough ass. Hence straw and more significantly supplemented straw feedingimproved botanical composition and animal production per unit area whileincreasing the potential for soil conservation.
Treatments had no significant effect on the soil bulk density up to the end of 6years and the water holding capacity up to the end of 3 years. By the end of 6years grazing cattle significantly increased the water holding capacity of the soilfrom G through OS to ass. Low inputs of resources available to farmers havethus produced increasing benefits with the passage of time and demonstrated thepotentials for the sustainability of a crop livestock integrated system