ABSTRACT
Phytotoxicity caused by secondary metabolites of botanical extracts is a drawback in agriculture. The objective of this study was to evaluate the phytotoxic effects of methanolic extracts of Crotalaria longirostrata and Argemone mexicana on the germination and physiological variables of tomato seedlings. The results indicated that high doses of both extracts (Clong500 and Amex500) inhibited tomato seed germination, while their mixture (Cl50 + Am50) promoted germination by 100%. At 30 days after transplanting (dat), the plant height increased by 15.4% with a high dose of C. longirostrata (Clong500) compared to the control. At 30 dat, the vigor index displayed a notable increase with Cl50 + Am50, reaching 29.5%. The root length increased with the mean dose of A. mexicana (Amex95) at 10, 20, and 30 dat (59.7%, 15.1%, and 22.4%, respectively). The chlorophyll content increased with Amex95 by 66.1% in 10 dat, 22.6% at 20 dat, and 19.6% at 30 dat. On the other hand, Amex95 had a higher nitrogen content throughout the trial. Amex95 produced the greatest increase in root dry weight by 731.5% and 209.4% at 10 and 20 dat. The foliage dry weight increased by 85.7% at 10 dat with Amex95 and up to 209.7% with Amex50 at 30 dat. The present investigation reveals the ability of the extracts to stimulate tomato growth at low and medium doses, though at high doses they exhibit allelopathic effects.
ABSTRACT
RESUMEN La calidad y disponibilidad del forraje, principalmente de las gramíneas, disminuye en las regiones tropicales durante la época seca, ya que al madurar incrementa el contenido de carbohidratos estructurales y disminuye el de proteínas y la digestibilidad. El objetivo de este trabajo fue evaluar el crecimiento inicial de Centrosema pubescens Benth, bajo fertilización nitrogenada y azufrada. La siembra de C. pubescens se realizó en bolsas negras de polietileno. Se evaluaron dos tratamientos de fertilización nitrogenada 0 kg/Nha-1 (-NS) y 44 kg/N-ha-1 (+NS), utilizando como fuente de nitrógeno sulfato de amonio. La fertilización se hizo al momento de la siembra, a los 15 d, 30 d y 60 d después de la siembra. El ensayo duró 12 semanas y se realizaron muestreos semanales de las siguientes variables: número de nódulos (NN), peso de nódulos (PN), longitud de raíz (LR), materia seca parcial (MSP), altura de planta (AP), índice de área foliar (IAF), tasa de acumulación neta (TAN), tasa de crecimiento del cultivo (TCC), tasa relativa de crecimiento (TRC) y área foliar específica (AFE). Se utilizó un análisis de regresión para estimar curvas de crecimiento y líneas de tendencia. El tratamiento +NS provocó la disminución significativa de NN (- 10) y PN (- 0.72 g) (P < 0.05). Resultados no significativos (P > 0.05) fueron observados en LR con 42.0 cm y 42.8 cm para +NS y -NS, respectivamente. Mientras que para MSP y AP, los tratamientos afectaron positivamente, el comportamiento (P < 0.05). El resto de las variables (IAF, TAN, TCC, TRC y AFE) no fueron afectadas por los tratamientos (P > 0.05). La fertilización con nitrógeno más azufre mejoró el establecimiento de C. pubescens con fines forrajeros.
ABSTRACT The quality and availability of forage, mainly from grasses, decreases in the tropical regions during the dry season, since when it matures it increases the content of structural carbohydrates and decreases the protein and the digestibility. The objective of this study was to evaluate the initial growth of Centro-sema pubescens Benth, under nitrogen and sulfur fertilization. The planting of C. pubescens was carried out in black polyethylene bags. Two treatments of nitrogen fertilization 0 kg/Nha-1 (-NS) and 44 kg/Nha-1 (+NS) were evaluated using ammonium sulfate as the nitrogen source. Fertilization was done at the time of planting, at 15 d, 30 d and 60 d after sowing. The experiment lasted 12 weeks and weekly sampling of the following variables was done: number of nodules (NN), nodule weight (NW), root length (RL), partially dry matter (PDM), plant height (PH), leaf area index (LAI), net accumulation rate (NAR), crop growth rate (CGR), relative growth rate (RGC) and specific leaf area (SLA). A regression analysis was used to estimate growth curves and trend lines. The +NS treatment caused a significant decrease of NN (- 10) and NW (- 0.72 g) (P < 0.05). Nonsignificant result was observed in RL (P > 0.05) with 42.0 cm and 42.8 cm for +NS and -NS, respectively. However, for PDM and PH the treatments affected positivity their behavior (P < 0.05). The rest of the variables (LAI, NAR, CGR, RGR and SLA) were not affected by the treatments (P > 0.05). Fertilization with nitrogen plus sulfur improved the establishment of C. pubescens for fodder purposes.
