No abstract

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).

No abstract

Soil nitrate tests are a useful tool to manage corn (Zea mays L.) N fertilization under rainfed conditions, but the feasibility of using these tests under irrigated Mediterranean conditions has received little attention. The objective of this study was to determine whether the preplant nitrate test (PPNT), pre-sidedress nitrate test (PSNT), and soil available-N content test (PPNT or PSNT plus N fertilizer) could accurately predict relative corn yield (RY) under irrigated, high-yielding conditions. Twentyone corn N-response experiments were conducted in Northeast Spain between 1999 and 2009. The trials were flood-or sprinklerirrigated. In each trial, three to six N treatments (from 0-300 kg N ha -1 ) were surface-applied to corn. Predictions of RY with the soil nitrate tests were low when the two irrigated systems were considered together (R 2 < 0.43). However, the available-N content provided moderately good predictions of RY for the sprinkler-irrigated fields (R 2 = 0.54-0.65) and poor predictions for the floodirrigated fields (R 2 = 0.17-0.36). The critical soil available-N content (0-30-cm soil depth) for maximum RY was established at 193 to 209 kg NO 3 -N ha -1 (»46-50 mg kg -1 ) for sprinkler-irrigated corn preceded by a cereal crop. These critical available-N values were lower when corn followed alfalfa and were greater than the critical PSNT levels reported for rainfed conditions in the Midwest and in Argentina (20-30 mg kg -1 ). The soil available-N content test could be a useful tool for managing corn N fertilization under sprinkler-irrigated Mediterranean conditions.