Suppressive effects of two composts, from cattle manure and grape marc, on the root-knot nematode Meloidogyne javanica were tested in pot and in vitro experiments. No root galls were found on tomato roots grown in soils containing 10 or 25% (v/v) cattle manure compost, and very few on those grown in 50% grape marc compost. Significant reductions in galling index were also found on tomato plants grown in soils containing lower concentrations of this compost. Chemical analysis of the composts and leachates from the soils showed that the cattle manure compost had higher electrical conductivity (EC) and higher concentrations of nitrogen, especially N–NH4, than the grape marc compost. Water extract of the cattle manure compost showed high nematicidal activity to the nematode juveniles and less activity toward the eggs in vitro. Water extract of the grape marc compost showed weaker nematicidal activity to the juveniles and eggs. Washing composted soils with excess water before nematode inoculation and tomato planting led to better plant growth, but the nematode-suppressive effect was decreased. These results suggest that high nitrogen concentrations, especially N–NH4, and high EC values contribute to the nematode suppressiveness of the composts.
Nitrate fertilizers are the most commonly used nitrogen sources for growing vegetables. The use of nitrate fertilizers in vegetable production may result in its accumulation in the plants if uptake exceeds assimilation. High nitrate concentrations in leafy vegetables represent a possible threat to human health. Leafy vegetables are the highest contributor to total food nitrate intake as a result of their high specific concentration and the large amount consumed. Consequently, European Union regulations were established for nitrate concentrations in leafy vegetables such as lettuce, spinach and rucola (Diplotaxis tenuifolia). Therefore, the need for a reliable, easy, fast and universal method to meet these demands is essential. We reassessed nitrate determination by comparing fresh and dry leaf material extracts of rucola. Our results indicate that the leaf nitrate concentration with both measurement methods is similar. Consequently, the use of the dry leaf extracts method is feasible and worth recommending to the European Union as an official method for determining nitrate concentrations in leafy vegetables.
Polyhalite is a hydrated sulfate of potassium (K), calcium (Ca) and magnesium (Mg) with the formula: K2Ca2Mg(SO4)4·2H2O. The main objective of the present study was to investigate and compare the efficiency of polyhalite as a fertilizer supplying K, Ca, Mg and sulfur (S) relative to equivalent soluble salts. The specific objectives were to investigate: 1. The release and transport of Ca, Mg, K and S in soil; 2. Uptake of these minerals by wheat plants and 3. Biomass production of wheat plants. To meet these objectives, two pot experiments (20 l pots filled with dune sand) were conducted in which the effects of four doses of polyhalite (0, 500, 1,500 and 2,500 kg/ha) and one dose of Ca, Mg and K sulfate salts (equivalent to the 1500 kg/ha polyhalite dose) were investigated. In a third experiment, residual effects of the fertilizers were studied using the pots from the first experiment. Different leaching fractions were used in the experiments (30% in the first one and 7–10% in the second and third experiments), to investigate the effect of water management on mineral transportation in the soil and plant uptake. Polyhalite was found to be a more efficient fertilizer for supplying K, Ca, Mg and S relative to equivalent soluble salts. To meet the plant required ratios for Ca, Mg and K, the polyhalite dose should be applied accordingly to provide sufficient Ca and Mg, and additional fertilizers should be used as a source of K. Transport and leaching of Ca, Mg, K and S in soil following polyhalite application was lower than following the application of the equivalent sulfate salts. The residual effect of polyhalite fertilizer on the subsequently grown crop was higher than the effect from the equivalent sulfate salts, especially regarding Ca, Mg and S. Irrigation management, as determined by the leaching fraction, has a strong impact on the efficiency of polyhalite as a source of K, Ca, Mg and S for plant nutrition.
Desalinated water has become a legitimate alternative water resource for the irrigation of intensive crops in semiarid regions. The concentrations of calcium (Ca) and magnesium (Mg) in water (CCa and CMg, respectively) supplied from desalinated plants are much lower than the values typically found in irrigation water resources in semiarid regions. blossom-end rot (BER), a physiological disorder at the blossom-end part of the fruit resulting in tissue disintegration and dehydration, is considered a Ca-related disorder and therefore the optimization of CCa has to consider not only total fruit production but also the occurrence of BER. There is a lack of information regarding the optimal CCa and CMg and Ca/Mg ratio in low-salinity water under Mediterranean conditions for high-quality yield of tomato fruits.
The main objective of the research was to optimize CCa and CMg for the production of high tomato fruit yield with minimal occurrence of BER. A secondary objective was to determine critical levels of Ca, Mg and Ca/Mg ratio in leaves in relation to yield and the occurrence of BER.
Tomato plants were grown in an inert media and fed with a wide range of CCa and CMg. Fruit yield was shown to decrease significantly when CCa was at or below 0.40 mmol l–1. In moderate CMg (1.4 mmol l–1) treatment, BER was negatively correlated to Ca level up to and including 1.4 mmol l–1 and was not manifested above that level under the prevailing conditions. Elevating CMg above 0.25 mmol l–1 enhanced BER occurrence. Concentrations of Ca and Mg in tomato organs increased with the respective mineral concentration in irrigation solution, whereas each element was reduced in organs as a function of the increased solution concentration of the other. The Ca concentration in diagnostic leaves (the diagnostic leaf is the fully developed youngest leaf) for optimal fruit yield with minimum BER was found to be 1.6%. The optimum CCa for high fruit yield with minimal BER occurrence was found to be in the range of 1.5–2.5 mmol l–1 combined with CMg at 0.25 mmol l–1.