It is difficult to establish agronomic practices for wheat (Triticum aestivum L.) production in Mediterranean regions because of high annual variability in rainfall. Plant density is a factor of particular importance in wheat production systems because it can be controlled. This study was conducted to determine the optimum seeding rates of Mediterranean types of wheat in irrigated Mediterranean systems. Field experiments were conducted under irrigation at two locations of the Ebro Valley, Spain, during two growing seasons, 1999–2000 and 2000–2001. Six seeding rates were compared: 150, 175, 250, 300, 400, and 500 seeds m−2 with four adapted wheat varieties including a hybrid wheat. Seeding rate affected grain yield and yield components in three of the four environments, but its effect varied with the environment. The plant densities giving the highest yields were at least 400 to 500 plants m−2 for most of the varieties studied. The results suggest that the rate of seeding under irrigation for Mediterranean areas might be higher than those used in other wheat‐growing areas.

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Fertilization of crops with liquid swine (Sus scrofa domesticus) manure (LSM) is a common practice throughout the world. In the Ebro Valley (northeast Spain) intensive swine production is very important and generates high quantities of LSM. Fertilizing maize (Zea mays L.) with LSM is a common waste disposal option. Nevertheless, continuous LSM application could have negative effects as heavy metal soil contamination could lead to plant toxicity. We assessed the effects of applying 29 and 51 m3 LSM ha−1 yr−1 to a field of maize during 6 yr. We measured the accumulation of total and extractable (EDTA) Cu and Zn in the soil and the concentration of these nutrients in maize plants and grain. During the 6 yr of the experiment a total of 6.6 to 11.9 kg Cu ha−1 and 12.8 to 22.5 kg Zn ha−1 (29 and 51 m3 LSM ha−1 yr−1, respectively) were applied to the soil. Total Cu and Zn soil concentrations increased by 32 and 11%, respectively, after 6 yr of LSM application. Extractable Cu and Zn soil concentrations increased more than 60% after 6 yr of consecutive LSM applications. It would take at least two to three centuries of regular LSM application to reach phytotoxic soil concentrations for Cu and Zn. Maize grain yields were about 13 to 14 Mg ha−1 over the 6 yr period, which also seems to confirm the absence of phytotoxicity. Copper and Zn concentrations in whole maize plants and grain during the last 2 yr of the experiment were lower than threshold values for animal and human ingestion (30 mg Cu kg−1 and 500–1300 mg Zn kg−1).