The International Center for Tropical Agriculture (CIAT), with support from the Inter-American Development Bank, has successfully developed a rice-pastures system where new rice varieties are cultivated alongside selected pasture grasses and legumes. Their research has brought the opportunity of making the savannas, all 243 million hectares of them, greener and healthier.
On-farm trials were conducted on the Matazul farm in Llanos Orientales, Columbia, from 1989 to 1993 as part of CIAT's long-term rice-pasture systems project. The site is characterized as having well-drained and flat lands with slopes <8%, and haplustox soils of intermediate to heavy texture. The experiment was specifically designed with plots large enough to permit grazing and the use of conventional machinery.
In 1989, two trials were conducted in 1 ha. plots with 3 replications, using the rice variety Line 3. The rice was planted in rows, and a mixture of grass/legume seed was broadcast over the planted crop. The grass/legume seed combination for the first plot consisted of Andropogon gayanus with Stylosanthes capitata and for the second plot was Brachiaria dictyoneura with Centrosema acutifolium.
The crops yielded, on the average, 2 t/ha with no significant differences between treatments. Establishment of the interseeded pasture species was excellent. Cattle weight gains during the first two years were higher than those recorded for similar pastures established with traditional methods. According to results from other trials in Carimagua, Meta, Columbia, an animal gains an average of 95 kg per year on a hectare of native savanna, but can gain 125 kg in improved grass pastures and 174 kg in grass-legume pastures. Animal performance declined in 1992, when the legumes were lost in both associated pastures and needed to be reseeded.
At the end of 1992, after one rice crop and three years of grazing, soil nutrient contents were comparable to, or slightly higher than, the original levels found in the native savanna soil (Table 1). This suggests that no degradation of the existing soil chemical properties occurred under the studied systems.
In 1993, the experiment was repeated on the same plots. Areas of 0.5 hectares were sown again with rice, using Line 3 in half the sown area and cv. Oryzica sabana 6, a new variety, in the remainder. In addition, a parallel small-plot experiment was established with the same treatments on native savanna.
The 1993 replication of the 1989 experiment significantly outyielded the results observed in 1989. Yields for Line 3 and Oryzica sabana 6 were approximately 165% and 183% of 1989 results. Yields of paddy rice of Line 3 were 2.9 and 3.7 t/ha after Brachiaria dictyoneura/Centrosema acutifolium and Andropogon gayanus/Stylosanthes capitata and for O. sabana 6 were 3.4 and 3.9 respectively. In the small plot experiment on native savanna, the highest yields were 3.1 from Line 3 and 2.7 t/ha from O. sabana 6. These results clearly show the benefits of three years of grazed-legume pastures.
Jose Ignacio Sanz
Apdo. Aéreo 6713, CIAT
E-Mail: CGI099 (CGNET)
Fax: (57-23) 6647243