Three years of field trials have been carried out in Zaragoza, Spain, using different biodegradable mulch materials in processing tomatoes. The aim was to evaluate weed control with several biodegradable mulches as alternatives to black polyethylene (PE) mulch. The treatments were rice straw, barley straw, maize harvest residue, absinth wormwood plants, black biodegradable plastic, brown kraft paper, PE, herbicide, manual weeding, and unweeded control. Assessments focused on weeds and on crop yield. A laboratory study showed that 1 kg/m2of organic mulch was sufficient to cover the soil for rice, barley straw, and maize harvest residue. The most abundant weed species in the field were purple nutsedge, common purslane, common lambsquarters, and large crabgrass and a change in weed composition was observed between treatments and years. Most weed species were controlled by the mulching materials except that purple nutsedge was controlled only by paper mulch. The other species were well controlled by PE and biodegradable plastic and also by some of the organic mulch treatments. Best weed control and lowest weed biomass were achieved by paper followed by PE and biodegradable plastic. The best organic mulch was rice straw and the worst weed control was from absinth wormwood. Tomato yield was highest for PE followed by paper, manual weeding, biodegradable plastic, and rice straw and was clearly related to weed control. Paper, biodegradable plastic, and rice straw are potential substitutes for PE and herbicides.

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Sprinkler irrigation can reduce the irrigation water needed to grow rice. However, most available information on weed control with herbicides is related to flood irrigated rice because this is the main growing method. Field experiments were conducted at Zaragoza (Spain) during two years to study weed control and tolerance of sprinkler irrigated rice to several herbicides. The main weeds were Atriplex prostrata Bouchér ex DC., Cyperus rotundus L., Echinochloa crus-galli (L.) Beauv. and Sonchus oleraceus L. Rice cv Guadiamar was tolerant to preemergence (PRE) application of clomazone at 0.36 kg ha -1 and oxadiazon at 0.5 kg ha -1 . PRE application of pendimethalin at 1.32 kg ha -1 combined with clomazone at 0.36 kg ha -1 decreased rice yield. Postemergence (POST) application of bentazon at 1.6 kg ha -1 + MCPA at 0.25 kg ha -1 did not injure rice but POST application of azimsulfuron at 0.025 kg ha -1 produced visual crop injury. Only treatments that controlled grassy weeds since rice was planted and by more than 80% at harvest time lead to acceptable rice yield (> 5,000 kg ha -1 ). Clomazone applied PRE at 0.36 kg ha -1 provided good control of grassy weeds (> 80%) and the highest rice yield, so it is recommended as a selective and efficacious PRE treatment for weed control of annual weeds in sprinkler irrigated rice. The perennial purple nutsedge was difficult to control at high plant densities (> 150 plants m -2 ) and the recommended herbicide is azimsulfuron applied at POST at 0.02 kg ha -1 . Additional key words: irrigation system; upland rice; weed competition. Resumen Selectividad de herbicidas y control de malas hierbas en arroz (Oryza sativa L.) regado por aspersiónEl riego por aspersion puede reducir el riego necesario en arroz. Sin embargo, casi toda la información sobre control de malas hierbas con herbicidas se refiere a arroz inundado por ser la forma principal de cultivo. Se realizaron ensayos de campo durante dos años para estudiar el control de malas hierbas y la selectividad de diversos herbicidas en arroz regado por aspersión. Las principales malas hierbas fueron Atriplex prostrata Bouchér ex DC., Cyperus rotundus L., Echinochloa crus-galli (L.) Beauv. y Sonchus oleraceus L. El arroz cv Guadiamar toleró las aplicaciones en preemergencia (PRE) de clomazona a 0,36 kg ha -1 y de oxadiazón a 0,5 kg ha -1 . La aplicación en PRE de pendimetalina a 1,32 kg ha -1 combinada con clomazona a 0,36 kg ha -1 disminuyó el rendimiento del arroz. La aplicación en postemergencia (POST) de bentazona a 1,6 kg ha -1 + MCPA a 0,25 kg ha -1 no afectó al arroz, pero la aplicación en POST de azimsulfurón a 0,025 kg ha -1 produjo fototoxicidad visual. Solamente los tratamientos que controlaron más de un 80% las gramíneas desde la siembra del arroz hasta la cosecha obtuvieron rendimientos aceptables de arroz (> 5.000 kg ha -1 ). La aplicación de clomazona en PRE a 0,36 kg ha -1 controló de forma eficaz las gramíneas (> 80%) y produjo los mayores rendimientos de arroz, recomendándose para el control de malas hierbas ...