Growth and N Fixation of Some Tropical Forage Legumes as Influenced by Solar Radiation Regimes¹

Abstract

Decreased solar radiation due to cloud cover or shading by plantation crops or associatedass can severely limit the production of tropical forage legumes. We therefore evaluated the response of six legumes (three replicated and three not replicated) to four radiation regimes (100, 70, 45, and 27% of unshaded solar radiation, hereafter termed "full sun") with polypropylene netting in the field. The three replicated legumes had significant yield reductions at 27% full sun, with intermediate reductions at 70 and 45%. Dry matter (DM) yields at full sun [metric tons (mt) ha-'yr-' and proportional yields at 27%] were: Desmodium intortum cv. Greenleaf (20.0, 46%); Centrosema pubescens 'centro' (13.7, 44%); and Macroptilium atropurpureum cv. Siratro (12.9, 20%). Greenleaf was relatively tolerant of moderate shading; proportional yields at 70 and 45% of full sun were 93 and 75%, respectively. Centro and Siratro yields declined linearly as shortwave radiation (hereafter termed "radiation") decreased, but Siratro yields declined significantly more than Centro. Marked seasonal differences were noted in the response of the legumes to shade, and this was attributed to differences in the ability of the legumes to utilize solar radiation during periods of cool temperatures. The three non-replicated legumes were evaluated similarly, except that yields were adjusted for replication effects. Dry matter yields and proportional yields at 27% full sun were: Leucaena leucocephala cv. Hawaiian Giant (23.5, 40 %); Stylosanthes guianensis cv gr. Schofield (17.0, 17%); and Desmodium canum `kaimi clover' (12.2, 32%). Hawaiian Giant and Greenleaf yielded similarly at 45 and 27% full sun. Kaimi clover DM yield tended to be slightly higher (13.8) at 70% full sun, but thereafter yields declined linearly with reduced radiation. Schofield stylo was the most sensitive to shading. Dry matter and N concentrations were not significantly elevated by reduced radiation or cool weather except that N increased during the cool season. Concentrations of N differed among species being highest for centro and Hawaiian Giant (3.4%) and lowest for kaimi clover (2.6%). Total N yields were associated with DM yields. Nitrogen yields (kg N ha-'yr-') of replicated legumes at full sun and proportional yields at 27% full sun were: Greenleaf (540, 45%), centro (461, 44%), and Siratro (362, 27%); and for the non-replicated legumes, Hawaiian Giant (751, 38%), Schofield (4%,18%), and kaimi clover [340 (361 at 70% full sun), 38%]. Acetylene reduction rates by nodules in soil cores were highly correlated with radiation regimes (r = 0.92-0.995; except for centro, r = 0.71.) Correlation of acetylene reduction rates with DM yields ranged from 0.80 to 0.996. The higher yielding legumes, Greenleaf, centro, and Hawaiian Giant (plus kaimi clover for ≈70% full sun only) appear well-suited for areas of low solar radiation because they have relatively constant concentrations of DM and N and fixed significant quantities of N even under dense shade.

Evaluation of tropical forage legumes under Pinus caribaea var hondurensis in Turrialba, Costa Rica

“…The results for these annual legumes with determinate flowering constrast with those obtained with six tropical forage legumes of indeterminate-flowering in Hawaii where at 27% full light only one species even flowered [7]. Flowering of indeterminate-flowering legumes is much more affected by shading than forage production [5].…”

“…Results of an experiment testing forage legumes under different shading levels [7] suggest that differences in shade tolerance between forage legumes are maintained at different light levels, i.e. a good performer at 25% full light will also perform well at 70% light.…”

Composição mineral de leguminosas forrageiras cultivadas sob diferentes níveis de sombreamento

“…O incremento da % de Ca +2 não é estimulado pela luminosidade (ERIKSEN;WHITNEY, 1982), no entanto, este estudo a % de Ca +2 apresentou influência dos níveis crescentes de sombreamento tanto na fração folha como na fração haste, nos dois períodos de avaliação. O que corrobora com Belsky (1992) A relação folha/haste das leguminosas forrageiras tropicais apresentou efeito linear negativo em função do nível de sombreamento (0, 30, 50 e 70% de retenção luminosa) durante o verão e outono, onde foi observado decréscimo médio de 0,2% na relação folha/haste para cada nível de sombreamento estudado em ambas estações.…”

Photosynthetic and leaf morphological characteristics in Leucaena leucocephala as affected by growth under different neutral shade levels

“…leucocephala increases its leaf area in low growth PPFD as would a facultative shade plant. L. leucocepha is considered to be shade tolerant because it has a relatively small decline in yield under shaded conditions as compared to other tropical forest legumes [6,7]. Potential physiological causes for this shade tolerance were explored in the present study.…”

“…Hawaiian Giant L. leucocephala (cv K8) is a particularly useful cultivar because of its high yield [5]. Since L. leucocephala is planted in shaded areas such as under crops, information on its response to shade is potentially useful for optimizing yield [7].…”