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The yield increase of vegetables, including common onion (Alium cepa L.), is of great interest to growers. However, higher yield often leads to what is known as genetic dilution of mineral density. A technology of onion fertilization based on elemental sulfur (S0) fertilizers seems to be a simple agronomic measure preventing a decrease in the nutrient concentration in onion bulbs. To verify this hypothesis, field studies were conducted in the 2009 and 2010 seasons. A two-factorial trial consisted of five sulfur fertilizers: Sw (crude form of S0), Sm (micronized S0), SmCu (Sm enriched with copper 0.25%), SmZn (Sm enriched with zinc 0.5%), and AS (ammonium sulfate); and, as the second factor, of two doses of S: 30 and 60 kg ha-1. The NPK plot, included as an independent experimental variant, was used as the control. Yield of onion increased by 13% in response to 30 kg S ha-1, and by 44% when fertilized with 60 kg S ha-1. The yield of bulbs was significantly affected by increasing magnesium and negatively by sodium concentration. The increase in both bulb yields and dry matter content resulted in a simultaneous decrease in nutrient density, except sulfur. The strongest dilution effect was observed for sodium (-33%), iron (-19%), magnesium (-17%) and phosphorus (-16%). Such a negative development can be prevented by applying sulfur fertilizers in an appropriate form. The concentrations of N, P, K, N, and Cu responded most demonstrably to the added ammonium sulfate. The concentrations of S, Zn, Cu, Mn, and Fe were affected by the micronized form of S0 enriched with zinc. The magnesium concentration was the highest in plants fertilized with the crude form of S0.
A way to alleviate excessive Mn nutrition of plants is through silicon application. The aim of the present study was to examine the effect of different Si concentrations in a nutrient solution and Si plant spraying treatments (in the form of silica sol) on the yielding and nutritional status of hydroponically grown lettuce under Mn-stress. The experiments were conducted under controlled conditions in a phytotron. The influence of the following Si levels in the nutrient solution (5.5 – control; 15.5; 23.25 and 31 mg Si dm-3) and foliar sprays (distilled water; Si solution) were investigated. Silicon supplied through fertigation significantly affected the plant’s nutrient status and alleviated the Mn stress, increasing fresh matter production, RWC (Relative Water Content) and the number of leaves per plants, while decreasing the share of dry matter. The Si nutrition did not change the content of Mn in the leaves, but caused a significant increase in N, P, Na, Fe and Si concentrations with a simultaneous decrease of Zn and Cu levels. The content of Ca, Mg and K was relatively stable (except for the treatment with the most intensive Si nutrition). Generally, the concentrations of N, P, K, Ca, Mg, Na and Fe within the tested Si range were higher than in the control, while being lower in the case of Zn and Cu. Overall, the foliar application of Si did not change plant yielding, the number of leaves on plants and most macro- and microelement concentration in leaves, but modified significantly the RWC as well as the Cu and Na content. The dry matter content under Si nutrition was varied. In summary, an effective method to alleviate Mn-stress is to apply silica sol to a nutrient solution used for plant fertigation.
Yields of oilseed rape harvested by farmers in Poland are usually much below the attainable potential of currently cultivated varieties, mainly because of the insufficient supply of nutrients during the yield foundation period, which determines the final number of secondary branches. This situation is typical of whole Poland, but may take place even on farms where high yields are harvested, for example in 2007. In 2006, 2007 and 2008, the year effect of multi-micronutrient fertilizers on yield of seeds, elements of yield structure and macronutrient content was studied. Multi-micronutrient fertilizers were applied twice over oilseed rape foliage during its pre-anthesis growth (BBCH45 and 53). In 2007, due to a drought in April, the harvested yields of seeds were below the country’s average. However, in each year of the study, a significant increase in the seed yield owing to the foliar application of multi-micronutrient fertilizers was found. The increase in the yield of seeds, averaged for the three years, reached 0.486 t ha–1 for the NPK+MiMo treatment (full set of micronutrients) and 0.36 t ha–1 for the NPK + Mi treatment (without molybdenum). The increments of the oilseed rape yield resulted from an increased number of developed secondary branches. This yield-forming element was an indirect result of the application of multi-micronutrient fertilizers, which affected the nitrogen economy by oilseed rape plants during the foundation period of their growth. At the same time, the increase in seed yield was significantly modified by the total number of developed pods, which is shaped during the yield-forming period of oilseed rape crop growth. Under conditions of the study, the magnesium content in secondary branches was found to be an element significantly correcting their number, thus increasing the yield of seeds.
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