Selections are made at four major field screening sites, which represent the major ecosystems where
Oxisols or Ultisols predominate. Promising grass and legume accessions are further tested in collabora-
tion with the International Tropical Pastures Evaluation Network (RIEPT, its Spanish acronym) through-
out the continent at more than 200 sites. Final selections are made for evaluation under grazing, on-farm
validation, and for eventual commercial release [205,215,216] (Table 3). The released grass and legume
cultivars require low fertilizer inputs, typically between 10 and 30 kg P ha^1 at planting, and fungicides
and insecticides are not applied because the forage cultivars are either resistant to or tolerant of major
pests and diseases.
In the Colombian savannas, a clear advantage has been demonstrated, both at the Carimagua research
station and on farm, in the performance of animals grazing on grass-legume pastures [207]. On-farm tri-
als in the Colombian Eastern Plains documented the excellent performance of forage cultivars recently
released to supplement native grasslands under conditions of farmer management [217]. An economic
analysis of the investment showed that the marginal rate of return of the grass-legume associations was
31% [203]. Similar trends are evident in results obtained throughout the humid tropics of Peru, Ecuador,
and Brazil. Some of the same species and accessions have also shown remarkably good adaptation to the
moderately acid soils of the Central American hillsides and humid Caribbean coasts. Furthermore, many
of these species have shown that they possess the ability to respond to increases in soil fertility.
- Physiological Aspects of Grass-Legume Associations
Several studies were conducted by CIAT researchers to determine differences in growth and development
of tropical forage grasses such as Andropogon gayanus,Panicum maximum, and Brachiariaspecies and
tropical forage legumes such as Stylosanthesspecies,Centrosemaspecies,Desmodium ovalifolium, and
Arachis pintoigrown as either monocrops or grass-legume associations under grazing [210,218–222].
598 RAO
TABLE 3 Tropical Forage Grasses and Legumes Formally Released as Commercial Cultivars for
Livestock Production on Low-Fertility Acid Soils of Tropical Latin America
Species CIAT accession number Countries where released
Grasses
Andropogon gayanus 00621 Colombia, Brazil, Venezuela, Panama,
Costa Rica, Perú, México, Cuba, Honduras,
Nicaragua, Guatamela
Brachiaria brizantha 06780 Brazil, Cuba, Venezuela, México, Costa Rica
B. Brizantha 26646 Colombia
B. decumbens 00606 Cuba, México, Panamá, Costa Rica
B. dictyoneura 06133 Colombia, Venezuela, Panamá, Costa Rica
B. humidicola 00679 Ecuador, Venezuela, Colombia, Panamá,
México
Panicum maximum 26900 Brazil
P. maximum 06962 Brazil
Legumes
Arachis pintoi 17434 Colombia, Brazil, Honduras, Costa Rica
A. pintoi Multiline Panamá
A. pintoi 18744 Costa Rica
Centrosema acutifolium 05277 Colombia
C. pubescens 00438 Honduras
Desmodium ovalifolium 00350 Brazil
Pueraria phaseoloides 09900 México
Stylosanthes capitata 10280 Colombia
S. guianensis 00184 Perú
S. guianensis 02950 Brazil
S. guianensis 02243 Brazil
S. macrocephala 01281 Brazil
Cliforia ternatea 20692 México, Honduras
Source: Adapted from Refs. 205, 215, and 216.