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.

Management practices, geographical gradients and climatic factors are factors explaining weed species composition and richness in cereal fields from Northern and Central Europe. In the Mediterranean area, the precise factors responsible for weed distribution are less known due to the lack of data and surveys. The existence of weed survey data of year 1976 in the Zaragoza province of the Aragón region, Spain, offered us the opportunity to compare present weed species with weed species growing 30 years ago. No detailed comparison of changes in weed species composition in cereal fields in that period of time has been conducted in the Mediterranean area. Here a survey was conducted in the Aragón region from 2005 to 2007. Weeds were surveyed in 138 winter cereal fields in ten survey areas where winter cereals are the main crops, using the same methodology applied 30 years ago. In the Zaragoza province, 36 fields were chosen in the same municipalities than in the previous survey. Several management, geographic and climatic variables of each field were recorded and related to weed species with multivariate analysis. Diversity index were calculated and related to survey area and altitude. Our results show that out of the 175 species only 26 species were found in more than 10% of the surveyed fields. The main species were Papaver rhoeas, Lolium rigidum, Avena sterilis and Convolvulus arvensis found in more than half of the surveyed fields. L. rigidum was related to dryland, while the other species were found overall. Furthermore, we found that management, geographical and climatic factors were significantly related to weed species distribution. In particular altitude, survey areas, irrigation and herbicide use in post-emergence were the most driving factors explaining weed species distribution. Species richness was higher in survey areas with extensive management practices and increased with altitude excepting a very productive area with intensive management practices at high altitude where richness was as low as in the irrigated lowlands. The main differences found between the 1976 and the 2005-2007 surveys were (1) the striking increase of grass weeds, (2) the high decrease of mean weed species number found in each field declining from 9 to 3 and (3) the frequency decrease of many weed species probably caused by agriculture intensification in that period of time. The growing importance of other weed species is probably related to their adaptation to minimum tillage, which is a widespread technique nowadays.

Inter-row hoeing is known to control tap-rooted and erect weed species more effectively in winter wheat than weed harrowing. However, little is known about its effectiveness for use in the spring in winter wheat grown at wide row spacing (240 mm) under the influence of different placement of fertilizer. Two field experiments, one in 1999 and one in 2000, were conducted to study the influence of fertilizer placement, timing of inter-row hoeing, and driving speed on the weeding effect on different weed species and crop growth. Placement of fertilizer below the soil surface improved crop growth and grain yield in both years compared with placement on the surface, but the more vigorous crop did not give any better suppression of the weeds surviving hoeing. Timing was not important in one experiment, whereas hoeing twice beginning in early April was more effective in the other experiment where weed growth over the winter had been vigorous. Driving speed had no influence on either the weeding effect or the yield, except for one case where increasing speed reduced the control of well-developed weeds. Compared with unweeded reference treatments, inter-row hoeing reduced total weed biomass by 60-70% and tap-rooted and erect weed species in particular by 50-90%. Sowing at 240 mm row spacing yielded less than 120 mm (Danish standard), and inter-row hoeing for winter wheat needs to be adapted to narrower row spacing to avoid such yield decreases.

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Summary Field trials were carried out at a single Danish and two Spanish locations. In Denmark, winter wheat was sown at 24‐cm row spacing allowing hoeing in the inter‐row area. Hoeing speeds of 2, 5 and 8 km h−1 were tested at the end of tillering, at the beginning of stem elongation or on both occasions. The crop was harrowed immediately after hoeing at the same speed. At the Spanish locations the winter barley was sown at a 12‐cm row spacing and harrowed only, at either pre‐emergence plus post‐emergence, or once post‐emergence at mid‐tillering at 2, 4, 6 and 8 km h−1. The depth of the soil layer thrown into the cereal row was measured at all locations. This layer ranged between 0.4 and 1.4 cm, depending on the site and on the treatment, but was generally higher following a single harrow treatment at all sites. The soil layer only tended to increase with faster speeds at the Danish location. On a more sandy soil and soil rolled prior to treatment, less soil was thrown into the cereal row. When two hoe + harrowing treatments were made, a finer soil structure was achieved. However, this did not affect the weed control. At the Danish location, initial intra‐row weeding efficacy of Brassica napus, based on plant number before and 7 days after treatment, was found to be low (21–41%) but increased to 74–79% when assessed after 45 days. Partial burial and bending of B. napus, together with crop competition, probably suppressed weed growth and enhanced final mortality. Uprooting was probably a more important cause of mortality for Stellaria media. At the Spanish locations, weeding efficacy of Papaver rhoeas was similar, ranging between 58% and 83% and this was achieved soon after harrowing. A thicker soil layer did not result in a greater weed kill. It was therefore suggested that burial alone could not be the main factor responsible for weed control in any of the cases studied. No reduction in wheat biomass, measured at the end of May, was found with increasing speed, or with repeated passes of the harrow. The results suggested that faster harrowing, which is economically more attractive for farmers, could be recommended. The soil layer thrown into the row was not found to be a useful parameter to predict the weed control efficacy in the cases presented.