Each crop may require a different root-zone temperature to achieve the maximum growth rate and yield. The temperature of the upper soil profile is determined by the soil properties, climate conditions, and site location, and can be either too high or too low for the crop requirements. A proper selection of plastic mulch can be used to modify the root-zone temperature to improve crop growth and yield. Cucumber plants grown in the field were exposed to different soil temperatures in two growing seasons under colored plastic mulches. Field studies were conducted during two growing seasons. Eight colored plastic mulches were tested at each growing season against bare soil. The objective of this study was to determine the effect of plastic mulch on heat accumulation as soil degree-day (DDsoil), photosynthesis rate, and yield of cucumber crop. The experimental design was a randomized complete block with nine treatments (eight colors of plastic mulch plus bare soil as the control) and four replications. The colors of the plastic mulches were: white-on-black, blue, white, black, black embossed, silver-on-black, red, and brown. DDsoil and plant photosynthesis were positively correlated with total yield, suggesting that increases in cucumber yield are due in part to an increase in soil temperature and plant photosynthesis. In conclusion, plants grown under the different colored plastic mulches had similar yields, and most of those plants had higher yields than plants grown in bare soil. We suggest that plastic mulch is useful for farmers of cucumber crops but the specific color of plastic mulch must be determined in each specific region.

The effect of different deficit-irrigation treatments on the dynamics of mineral nutrients in leaves of peach trees growing under Mediterranean conditions was studied. Treatments consisted of a control, continuous deficit irrigation, regulated deficit irrigation, and partial root drying. The dynamics of nutrients were unchanged by the water deficits, though the amount absorbed was slightly modified. The advantages of deficit-irrigation strategies with regard to water-use efficiency were accompanied by the absence of any harmful effect on leaf mineral nutrition.

The effect of row covers on watermelon (Citrullus vulgaris) grown on plastic mulch is well documented. However, row covers have not been adequately evaluated under Mexican growing conditions. Watermelon plants were grown on plastic mulch alone or with row covers to study their effect on photosynthesis, and early and total yields. Treatments were clear plastic mulch (C); black plastic mulch (B); B plus a Vispore cover of polypropylene (BV); B plus a white cover of perforated polyethylene (BW); B plus a clear cover of perforated polyethylene (BC); B plus an Agribon cover of polypropylene (BA); and bare soil as the control. For plants grown in treatment C, B or B combined with row covers, plant dry weight and number of leaves 40 days after seeding (DAS) were higher than the control (P<0.05), except BC which was comparable to the control. Total yields of treatments C, B, BV, BW and BA differed (P<0.05) from BC and the control. Total yields increased by 46.1, 43.2, 35.7, 41.6, 13.3, 15.4 and 35.8 t/ha for the C, B, BV, BW, BC and BA treatments, respectively, over the control, which yielded 27.1 t/ha. Total yield was highest for the C and the B treatment suggesting that there was no need for additional covers. The number of leaves per plant or dry weight per plant better explains the changes in yield than net photosynthesis rate. Stomatal conductance was explained in part by changes in photosynthesis.

No abstract

En esta investigación se evaluó la influencia de la calidad e intensidad de luz en el crecimiento y absorción total de nutrimentos en el cultivo de lechuga romana tipo baby. Las variables de crecimiento evaluadas fueron: peso fresco y seco de raíz y hojas, número de hojas y absorción total nutrimental (N, P, K, Ca, Mg, Cu y Zn). Los resultados evidenciaron diferencias significativas entre tratamientos (p ≤ 0,05), destacando un mayor crecimiento del cultivo bajo el tratamiento de luz roja + azul + suplemento de luz blanca, tanto en peso seco y fresco, número de hojas y absorción total de nutrimentos, demostrando así que, a mayor intensidad de luz, considerando su calidad (espectros electromagnéticos irradiados), se promueve un mayor crecimiento en el cultivo. La eficiencia energética en la producción de peso seco con respecto a la intensidad de luz acumulada se vio disminuida en el tratamiento 3 debido a que el suplemento de luz blanca proporcionó otros espectros electromagnéticos que no son tan eficientes en los procesos fotosintéticos comparados con el rojo y azul (tratamientos 1 y 2); requiriendo una intensidad de luz acumulada de 1,87 mol•m -3 para producir 1,0 g de peso seco, valor superior al tratamiento 1 (1,57 mol•m -3 ) y tratamiento 2 (1,53 mol•m -3 ).