IS IT POSSIBLE TO REDUCE NITROGEN FERTILIZATION IN PROCESSING SPINACH?

A two-year field experiment was carried out in a typical Mediterranean environment (Foggia, Southern Italy) to evaluate the effect of the reduction of nitrogen (N) fertilization on yield, quality, N uptake, N utilization efficiency, and on environmental impact of processing spinach (Spinacia oleracea L.). In a completely randomized experimental design with four replications, 50, 75, and 100% (150, 225, and 300 kg N ha^?1, respectively) of the normal rate applied by the farmers in the trial area were compared. In both years, the total amount of the urea fertilizer applied was broadcasted three times. The results obtained indicate that a lower N fertilization level ensured a satisfactory yield, increased quality and N utilization efficiency. However, crop performances and the amount of N available for leaching were dependent by the weather conditions occurred during plants growth, being significant the year × N fertilization rate interaction.     

DOES NITROGEN FERTILIZATION ENHANCE DROUGHT TOLERANCE IN SUNFLOWER? A REVIEW

Water stress is one of the major limitations to the agricultural productivity around the globe, particularly in warm, arid and semi-arid regions of the world. Sunflower (Helianthus annuus L.), being a crop with medium water requirements, has the ability to tolerate a short period of drought. However, water stress in the soil as well as inside the plant influences various physiological and biochemical processes. This may inhibit plant growth, decrease developmental activities of the cells and tissues and cause a variety of morphological, physiological and biochemical modifications. Nitrogen (N) is one of the most important mineral nutrients because of its numerous effects on plant growth and yield. A number of fundamental processes such as water and nutrient uptake, protein metabolism, photosynthesis, carbon partitioning, and enzyme and plant hormonal activities are regulated by N. These responses result in profound changes in growth rate, net photosynthate production, plant development, and yield. It is well documented that nutrient uptake of plants is inhibited in dry soils and with expected nutrient deficiencies the normal functioning of the plants is affected. Different strategies are being practiced in the world to cope with the problem of nutrient deficiency under water stress. Nitrogen application either through soil or through foliar feeding is an important strategy to alleviate the adverse effect of drought. Supplemental application of N as foliar fertilization to soil-applied fertilization is important in situation where nutrient supply through soil is limited. Some of the relevant work available about the effect of water stress and nutrient availability in sunflower is reviewed in this paper.     

EFFECTS OF SALINITY ON ACCUMULATION OF MINERAL NUTRIENTS IN WHEAT GROWN WITH NITRATE–NITROGEN OR MIXED AMMONIUM:NITRATE–NITROGEN

ABSTRACT

Two cultivars of wheat (Triticum aestivum cvs. Fresco and Hussar) were grown in hydroponic culture with nitrogen (N) supplied either as nitrate or equimolar ammonium and nitrate, and with a range of concentrations of NaCl from 0 to 100 mM. Plant growth was stimulated by low concentrations of NaCl and was depressed by high concentrations of NaCl. Growth was higher with mixed N nutrition than with nitrate supplied alone at all rates of NaCl supply. Shoot:root ratio was also depressed by salinity. Concentrations of potassium (K) decreased with salinity and were generally higher with mixed N supply, whereas concentrations of Na were higher with salinity and lower with mixed N supply. There were strong positive linear relationships between total plant dry mass and the concentrations of copper (Cu) in the roots and strong negative linear relationships between total plant dry mass and the concentrations of manganese (Mn) in both shoots and roots and zinc (Zn) in the shoots. The concentrations of Cu in the roots were higher with mixed N supply, lower with high salinity, and the concentrations of Mn in both shoots and roots were lower with mixed N supply and generally higher with high salinity. Tissue concentrations of these ions appear to be major determinants of wheat growth in saline environments.     

CHLOROSIS IN WILD PLANTS: IS IT A SIGN OF IRON DEFICIENCY?

ABSTRACT

Chlorosis in crops grown on calcareous soil is mainly due to iron (Fe) deficiency and can be alleviated by leaf application of soluble Fe²⁺ or diluted acids. Whether chlorosis in indigenous plants forced to grow on a calcareous soil is also caused by Fe deficiency has, however, not been demonstrated. Veronica officinalis, a widespread calcifuge plant in Central and Northern Europe, was cultivated in two experiments on acid and calcareous soils. As phosphorus (P) deficiency is one of the major causes of the inability of many calcifuges to grow on calcareous soil we added phosphate to half of the soils. Leaves in pots with the unfertilized and the P-fertilized soil, respectively, were either sprayed with FeSO₄ solution or left unsprayed. Total Fe, P, and manganese (Mn) in leaves and roots and N remaining in the soil after the experiment were determined. In a second experiment, no P was added. Leaves were either sprayed with FeSO₄ or with H₂SO₄ of the same pH as the FeSO₄ solution. Degree of chlorosis and Fe content in leaves were determined. Calcareous soil grown plants suffered from chlorosis, which was even more pronounced in the soils supplied with P. Newly produced leaves were green with Fe spray but leaves that were chlorotic before the onset of spraying did not totally recover. H₂SO₄ spray even increased chlorosis. This demonstrated that chlorosis was due to Fe deficiency. As total leaf Fe was similar on acid and calcareous soil, it was a physiological Fe deficiency, caused by leaf tissue immobilization in a form that was not metabolically “active”. Iron in the leaves was also extracted by 1,10-phenanthroline, an Fe chelator. In both experiments, significant differences between leaves from acid and calcareous soil were found in 1,10-phenanthroline extractable Fe but not in total leaf Fe, when calculated on a dry weight basis. Differences in 1,10-phenanthroline extractable Fe were more pronounced when calculated per unit dry weight than calculated per leaf area, whereas the opposite condition was valid for total leaf Fe.