The increased salinity of arid and semi‐arid lands has become a problem of great concern in agriculture. The possibility that the inhibition of leaf growth in alfalfa (Medicago sativa) growing under saline conditions may be associated with a reduction in ion concentration in the leaf was investigated. Seeds of alfalfa cv. Buraimi were sown in PVC cylinders filled with loamy sand and arranged in large pots embedded in the soil with the rim just above the soil surface. This arrangement simulated plants grown under field conditions. Seedlings were irrigated with saline (12.2 dS m−1) and nutrient solutions (full strength or 20 times dilution) twice weekly. After 6 weeks the plants were harvested and separated into roots, stem and leaves. The leaves were further separated into lamina and petioles and analysed for the major and minor nutrient elements. Salinization significantly reduced the fresh weights of the roots, stem and leaves as well as the concentration of N, K, Ca and Mg in the leaf tissue. With the exception of Cu concentration, which was enhanced by salinity, all the micronutrients (B, Zn, Mn and Fe) had reduced concentrations in the leaves of salinized alfalfa. The application of an external nutrient solution, especially the full‐strength solution, produced an increase in leaf growth and leaf nutrient element concentration. On the basis of these results it was concluded that reduced leaf nutrient concentration may be one of the primary causes of the inhibition of leaf growth that was characteristic of alfalfa growing under salinity stress.

In orange commercial farms, Zn deficiencies symptoms and small fruits were observed in Corrientes, Argentine. During four years (1995 to 1998), Valencia orange (Citrus sinensis Osb.) on Rough lemon (C. jambhiri Lush.) rootstock, implanted in 1974 in sandy soil, where six treatments were tested. Treatments varied from 1 to 3 Kg KCl.tree-1.year-1 (applied in April and December) with and without Zineb 80, 0,35%. year-1, 20 L. tree-1 (13,3 g Zn.tree-1 applied in December). The experimental design was a randomized complete block with four replications, with a single tree and borders in the experimental plot. Foliar sample were taken every year in Autumn and Summer, foliar concentrations of Zn and K were determined by atomic spectrum absorption. Harvested fruits were classified into small, medium and big. Analysis of Variance, Tukey test and Pearson correlations between production and foliar concentrations were performed. Higher fertilization levels of K with Zn increased medium and big fruits production (Kg and percentage). Foliar concentrations of K and Zn were positively correlated with big and medium fruit production and negatively correlated with small one. Chemical names used: Ethilenbis-ditiocarbamate of Zn (Zineb).

Para evaluar la efectividad del pyraclostrobin en comparación con otros fungicidas para el control de la mancha negra de los cítricos (MNC), en lotes comerciales de naranjo 'Valencia late' en Corrientes, Argentina, se probaron diferentes combinaciones de dosis, frecuencias y momentos de aplicación de pyraclostrobin 25%, mancozeb 80% y benomyl 50%. Se encontraron condiciones ambientales favorables para el desarrollo de MNC durante la primavera, con menor infestación en el sector sudoeste de las plantas. La mayor eficiencia de control de MNC (95.5 % frutos grado 0), se obtuvo con 30 mL de pyraclostrobin aplicado en tres momentos (octubre, noviembre y enero). Debido al riesgo de aparición de resistencia a las estrobilurinas por tres aplicaciones por campaña, sería recomendable su uso en dos aplicaciones tardías (noviembre y enero), que permitieron obtener entre 75 y 88% de frutos sin síntomas.

RESUMEN -El objetivo del trabajo fue evaluar el efecto del 3,4-dimetilpirazol fosfato (DMPP) en la eficiencia de la fertilización amoniacal, en naranjo dulce [Citrus sinensis (L.) Osbeck] 'Valencia late' sobre suelo arenoso, en la provincia de Corrientes, Argentina. Durante tres campañas se trabajó en un huerto de naranjo 'Valencia late' injertado sobre lima de Rangpur (Citrus limonia, Osbeck), sobre un suelo tipo Udipsamment alfico. Se utilizó un Diseño de Bloques Completos al Azar con cuatro repeticiones, parcela útil una planta más borduras, con los tratamientos: 1. (Testigo) 150 kg de N ha -1 (fertilizante 15-6-15-6); T2. 75 kg de N ha -1 (sulfonitrato de amonio (SNA) 26 % N) tratado con DMPP (0,8% respecto al N amoniacal); T3. 150 kg de N ha -1 (SNA 26 % N), tratado con DMPP (0,8% respecto al N amoniacal). En el otoño se tomaron muestras foliares de ramas fructíferas, determinándose contenido de N, P y K. En la cosecha se determinó producción por planta (kg) y se evaluó calidad de frutos. Los resultados obtenidos permiten establecer que en suelos arenosos, el agregado de DMPP mejora la eficiencia de la fertilización nitrogenada. Con igual aporte nitrogenado, se incrementan los rendimientos y las concentraciones foliares de N y con la mitad de la dosis se logran rendimientos equivalentes al testigo. Palabras clave: Inhibidores nitrificación -Citrus sinensis -fertilización -productividad. 3,4-DIMETHYLPYRAZOLE PHOSPHATE (DMPP) EFFICIENCY IN SWEET ORANGE IN ARGENTINA NORTHEASTABSTRACT -The aim of this study was to evaluate the 3,4-dimethylpirazol phosphate (DMPP) effect on the efficiency of ammonium-N fertilization on sandy soil of Corrientes, Argentina. The experiment was carried out with sweet orange [Citrus sinensis (L.) Osbeck] 'Valencia late' grafted on Rangpur lime (Citrus limonia, Osbeck) rootstock under field conditions during three consecutive years, the orchard was established on an alfic Udipsamment soil. A randomized complete block statistical design with four replications was used and the treatments were: 1. (Control) 150 kg N ha -1 (fertilizer 15-6-15-6); 2. 75 kg N ha -1 (ammonium sulphonitrate (SNA) 26% N) treated with DMPP (0.8% compared to ammonia N); 3. 150 kg N ha -1 (SNA 26% N), treated with DMPP (0.8% compared to ammonia N). Leaf samples from fruitful branches were taken in autumn and the amount of N, P and K were analysed. At harvest, yield per plant was measured (kg) and quality of fruits was assessed. The results obtained demonstrate that in sandy soils, the addition of DMPP improves the efficiency of nitrogen fertilization. Identical nitrogen supply, increase yields and foliar concentrations of N and with the half N dosage, control equivalent yields were achieved.

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