Predictive theory on how plant diversity promotes herbivore suppression through movement patterns, host associations, and predation promises a potential alternative to pesticide-intensive monoculture crop production. We used meta-analysis on 552 experiments in 45 articles published over the last 10 years to test if plant diversification schemes reduce herbivores and/or increase the natural enemies of herbivores as predicted by associational resistance hypotheses, the enemies hypothesis, and attraction and repellency model applications in agriculture. We found extensive support for these models with intercropping schemes, inclusion of flowering plants, and use of plants that repel herbivores or attract them away from the crop. Overall, herbivore suppression, enemy enhancement, and crop damage suppression effects were significantly stronger on diversified crops than on crops with none or fewer associated plant species. However, a relatively small, but significantly negative, mean effect size for crop yield indicated that pest-suppressive diversification schemes interfered with production, in part because of reducing densities of the main crop by replacing it with intercrops or non-crop plants. This first use of meta-analysis to evaluate the effects of diversification schemes, a potentially more powerful tool than tallies of significant positive and negative outcomes (vote-counting), revealed stronger overall effects on all parameters measured compared to previous reviews. Our analysis of the same articles used in a recent review facilitates comparisons of vote-counting and meta-analysis, and shows that pronounced results of the meta-analysis are not well explained by a reduction in articles that met its stricter criteria. Rather, compared to outcome counts, effect sizes were rarely neutral (equal to zero), and a mean effect size value for mixed outcomes could be calculated. Problematic statistical properties of vote-counting were avoided with meta-analysis, thus providing a more precise test of the hypotheses. The unambiguous and encouraging results from this meta-analysis of previous research should motivate ecologists to conduct more mechanistic experiments to improve the odds of designing effective crop diversification schemes for improved pest regulation and enhanced crop yield.

No abstract

La oferta hídrica neta hace referencia al agua que emplea el hombre para sus diferentes usos como:agricultura, industria, doméstico y recreación; en Colombia se determina aplicando la Resolución 0865del 2004 del Ministerio de Ambiente, Vivienda y Desarrollo Territorial, donde a la oferta superficial seaplican dos factores de reducción correspondientes a un 25% por caudal ecológico y 25% por calidad delagua. La aplicación de estas dos reducciones se ha limitado en la mayoría de los casos, al aplicar estosporcentajes al caudal medio mensual multianual más bajo, por lo tanto, los estudios de calidad no seincluyen directamente en este cálculo. En este artículo se presenta la metodología para calcular lareducción correspondiente a la calidad del agua, a partir de la determinación de los indicadores de calidady contaminación, ICA e ICO, utilizando información de dos subcuencas tributarias al río Cauca: ZanjónOscuro y Río Hondo, localizadas en la cuenca alta del río Cauca, encontrando una relación directa entre lareducción y la contaminación del agua.

1 Recibido: 15 de junio, 2016. Aceptado: 7 de noviembre, 2016. Este trabajo hizo parte del proyecto de investigación CI 2805 "Manejo integrado del riego y la fertilización nitrogenada en sistemas productivos de plantas aromáticas" financiado por la Universidad ResumenEl presente trabajo tuvo como objetivo determinar las necesidades hídricas a partir de la curva de coeficiente de cultivo (Kc) para estevia (Stevia rebaudiana Bertoni) en Candelaria, Valle del Cauca, Colombia. El experimento se desarrolló durante el primer semestre de 2015. En una parcela cultivada con estevia se establecieron tres lisímetros de drenaje dispuestos al azar y una estación metereológica portátil para la determinación de las variables climatológicas necesarias para el cálculo de la evapotranspiración de referencia (ETo), con el empleo de la ecuación de Penman Monteith. Se determinó la humedad de capacidad de campo del suelo y se realizó un seguimiento periódico tanto de la humedad del suelo como de la lámina de drenaje. La lámina de riego fue aplicada con base en un coeficiente de agotamiento del 10% para llevarlo nuevamente a capacidad de campo. Se realizaron los análisis estadísticos de normalidad, homogeneidad de varianzas y regresiones, y se calculó el Kc para cada etapa fisiológica, a partir del cociente entre la evapotranspiración del cultivo (ETc) y ETo. Con 95% de confianza los Kc para estevia fueron: etapa de crecimiento (54 días después del trasplante ddt) 0,86 ± 0,12, etapa de madurez (55 -72 ddt) 1,24 ± 0,10 y etapa de senescencia (72 -96 ddt) 0,85 ± 0,14. El consumo de agua de Stevia rebaudiana B., fue de 4753 m 3 /ha, durante su ciclo de cultivo de 96 días después del trasplante.Palabras claves: balance hídrico, agua de drenaje, evapotranspiración, Stevia rebaudiana Bertoni. AbstractThis study aimed to determine the crop coefficient (Kc) curve for stevia (Stevia rebaudiana Bertoni) in Candelaria, Valle del Cauca, Colombia. The experiment was conducted during the first half of 2015. In a plot planted with stevia, were located three drainage lysimeters arranged randomly and a portable weather station to determine climatic variables necessary for calculating an evapotranspiration reference (ETo), using the Penman Monteith equation. Soil field capacity moisture was determined and regular monitoring of both, soil moisture and drainage water depth were performed. Irrigation was applied using an exhaustion coefficient of 10% to bring it back to field capacity Nota técnica

Estimating nitrogen (N) concentration in situ is fundamental for managing the fertilization of the sugarcane crop. The purpose of this work was to develop estimation models that explain how N varies over time as a function of three spectral data transformations in two stages (plant cane and first ratoon) under variable rates of N application. A randomized complete-block experimental design was applied, with four levels of N fertilization: 0, 80, 160, and 240 kg N ha −1 . Six sampling events were carried out during the rapid growth stage, where the canopy reflectance spectra with a hyperspectral sensor were measured, and tissue samples for N determination in plant cane and first ratoon were taken, from 60 days after emergence (DAE) and 60 days after harvest (DAH), respectively, until days 210 DAE and 210 DAH. To build the models, partial least squares regression analysis was used and was trained by three transformations of the spectral data: (i) average reflectance spectrum (R), (ii) multiple scatter correction and Savitzky-Golay filter MSC-SG) reflectance spectrum, and (iii) calculated vegetation indices (VIs).