surface water pollution are causing swine and dairy producers to reconsider their management strategies (Bo-Alfalfa (Medicago sativa L.) may not be the most suitable crop det et al., 2001; Soil and Water Conserv. Soc., 1998; to utilize all the manure nutrients, but it may be the best crop available, especially when the crop is dormant. The objective of this research was Dané s et al., 1995). to investigate the effect of swine (Sus scrofa domesticus) slurry manure In several alfalfa-producing areas, alfalfa and maize on alfalfa yield and the concentration of nutrients in soil. A 2-yr field are important irrigated crops, and swine growing is one experiment was initiated in 2001 on two soils: a Typic Xerofluvent of the main animal production activities. Alfalfa has and a Calcixerolic Xerochrept. Soil mineral elements were extracted become an alternative crop although alfalfa fields may with ammonium bicarbonate diethylenetriaminepentaacetic acid, and not be the best possible location for manure applicainitial extractable P and K were 16.7 and 6 mg P kg Ϫ1 and 152 and tions. As reported by Kelling and Schmitt (1996) in 103 mg K kg Ϫ1 for the two soils, respectively. There were four treat-Wisconsin, topdress applications of manure on alfalfa ments: annual winter applications of 25 and 50 m 3 ha Ϫ1 of swine slurry are often made because of necessity rather than choice. manure, annual fertilization of 32.75 kg P ha Ϫ1 and 125 kg K ha Ϫ1 , These may be the only fields available at some times and a no-manure or fertilizer control. Application of slurry manure in winter was not detrimental to the crop. Manure and fertilizer treat-of the year and, on many farms, the best environmental ments increased alfalfa dry matter (DM) yield 37% on the low-fertility alternative (Kelling and Schmitt, 1996). soil. There was no significant effect of manure or fertilizer on alfalfa Manure application on alfalfa has been considered a DM yield on the Xerofluvent soil. Application of the slurry slightly risky management practice by many because it may increased the soil concentrations of P, Mg, Zn, and Fe in highercause plant injury or stand reduction of the alfalfa due fertility soils and copper in low-fertility soils. The 2-yr results suggest to the salts contained in the manure and physical damthat the application of slurry in soils with low levels of trace elements, age to the crowns during application, mainly in the such as those used in the trials, does not produce a significant buildup wheel-track areas (Kelling and Schmitt, 1996; Lory et of these elements that could lead to an environmental problem.

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.

Timely sowing is critical for maximizing yield for both grain and biomass in maize. The effects of early (mid-March), normal (mid-April), and late (mid-May) sowing date (SD) were studied over a three-year period in irrigated maize under Mediterranean conditions. Early SD increased the number of days from sowing to plant emergence. Late SD reduced the number of days to plant maturity, and had higher forage yields, higher grain humidity, and taller plants. The average grain and forage yields achieved were 13.2 and 21.3 Mg ha−1; 14.0 and 25.1 Mg ha−1; and 12.8 and 27.6 Mg ha−1, for crops with early, normal, and late SD, respectively. The data support the general perception of farmers that April sowings are the most appropriate in the area where the experiments were carried out. Early SD resulted in lower population densities, while later SD did not yield (grain) as high. However, late SD produced taller plants that contributed to achieve higher forage yields. Late SD could be interesting for double annual forage cropping systems. Sowing at the most appropriate time, when the soil is warm, ensures a good level of maize grain production. Future research could focus in the effect of SD for total annual yields in double-annual cropping systems

In crop rotations that include alfalfa (Medicago sativa L.), agronomic and environmental concerns mean that it is important to determine the N fertilizer contribution of this legume for subsequent crops in order to help to increase the sustainability of cropping systems. To determine the N fertilizer replacement value (FRV) of a 2-yr alfalfa crop on subsequent crops of corn (Zea mays L.) followed by wheat (Triticum aestivum L.) under irrigated Mediterranean conditions, two 4-yr rotations (alfalfa-corn-wheat and corn-corn-corn-wheat) were conducted from 2001 to 2004 in a Typic Xerofluvent soil. Corn yields were compared after two years of alfalfa and a third year of corn under monoculture and wheat yields were also compared after both rotations. Corn production after alfalfa outyielded monoculture corn at all four rates of N fertilizer application analyzed (0, 100, 200 and 300 kg N ha -1 ). The FRV of 2-yr alfalfa for corn was about 160 kg N ha -1 . Wheat grown after the alfalfa-corn rotation outyielded that grown after corn under monoculture at both the rates of N studied (0 and 100 kg N ha -1 ). The FRV of alfalfa for wheat following alfalfa-corn was about 76 kg N ha -1 . Soil NO 3 --N content after alfalfa was greater than with the corn monoculture at all rates of N fertilizer application and this higher value persisted during the second crop after alfalfa. This was probably one of the reasons for the better yields associated with the alfalfa rotation. These results make a valuable contribution to irrigated agriculture under mediterranean conditions, show reasons for interest in rotating alfalfa with corn, and explain how it is possible to make savings when applying N fertilizer.Additional key words: crop rotations, fertilizer equivalent, FRV, maize, N contribution, N credit. Resumen Valor de sustitución del nitrógeno procedente de la alfalfa para el maíz y el trigo en regadío en la zona mediterráneaEn las rotaciones que incluyen alfalfa (Medicago sativa L.), ésta aporta a los cultivos siguientes una cantidad de N que conviene cuantificar como medida de sostenibilidad. Para determinar el N equivalente o valor de sustitución de N (FRV) de una alfalfa de dos años en el maíz (Zea mays L.) cultivado posteriormente y el trigo (Triticum aestivum L.) subsiguiente en los regadíos mediterráneos, se estudiaron dos rotaciones de 4 años (alfalfa-alfalfa-maíz-trigo y maíz-maíz-maíz-trigo) entre 2001 y 2004 en un suelo Typic Xerofluvent. Se comparó el rendimiento del maíz con dos precedentes distintos: a) 2 años de alfalfa y b) 2 años de maíz, y, posteriormente, el rendimiento del trigo en ambas rotaciones. Las producciones de maíz después de alfalfa superaron las del maíz en monocultivo en las cuatro dosis de fertilizante estudiadas (0, 100, 200 y 300 kg N ha -1 ). El FRV de una alfalfa de 2 años para el maíz se evaluó en unos 160 kg N ha -1 . El trigo después de la rotación alfalfa-maíz dio mayores rendimientos que el producido después del monocultivo de maíz para las dos dosis ensayadas (0 y 100 kg N ha -1 ). El ...