Marzena Sylwia Brodowska
Mineral fertilization as a factor determining the sulphur effect on the yield, chemical composition and quality of cultivated plants
zeszyt 380, ss. 159
The study was conducted to determine the optimal N:P:K ratio and magnesium rate (pot experiment) as well as N:P:K:Mg ratio (field trial) as factors determining the effect of sulphur in order to achieve high and also good crops (in terms of quality) of tested plant species (spring oilseed rape and winter barley, spring and winter wheat, spring barley). Hence, the pot and field experiment was carried out. The three-year pot experiment was conducted in 2004–2006 in the greenhouse using the soil material taken from the topsoil with a particle size of brown sandy loam. The experiment established by means of a complete randomization included three variable factors: sulphur dose, magnesium rate, and N:P:K ratio applied at three levels. Spring oilseed rape (Brassica napus L.), spring wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) were the test plants. The field experiment was conducted in four replications by mans of a randomized sub-blocks design in a dependent system (split-plot), on the brown soil developed from loess with a particle size of dusty clay. The field experiment was conducted in rotation with four plant species: winter oilseed rape (Brassica napus L.), winter wheat (Triticum aestivum L.), spring barley (Hordeum vulgare L.), and sugar beet (Beta vulgaris L.).
Presented study – both in pots and field – carried out on the soil with low sulphur abundance supported its significant impact on the quantity and quality of crops achieved. This refers not only to plants commonly considered to be „sulphurophilic” such as oilseed rape, but also species with low requirements for this element, such as wheat or barley. Among studied experimental factors, the sulphur dose exerted the greatest impact on yields of seed, grain, and straw of spring forms of oilseed rape, wheat, and barley. Considering the pot experiment, only the oilseed rape seeds were produced due to the higher dose of sulphur. The best yield-forming effect in the case of spring oilseed rape was recorded for higher sulphur rate, and in the case of spring wheat and spring barley – lower dose of the element. A positive effect of sulphur fertilization on yield of winter oilseed rape was also observed in a field experiment. In the case of winter wheat and spring barley, the sulphur effect on crop yielding was determined by N:P:K:Mg ratio. In the field experiment, sulphur fertilization was associated with a significant increase in 1000-grain weight of oilseed rape, while a decrease of the parameter for barley.
Presented pot and field studies support the conclusion that the dose of sulphur differentiated the content of total nitrogen and total sulphur, as well as the ratio of total N to total S in the test plants to the highest extent. Sulphur fertilization affected the significant increase in the total sulphur content in plants and the reduction in N total to S total ratio. In the pot experiment, the highest protein nitrogen content along with its largest percentage in the total nitrogen was found in the oilseed rape seeds at N:P:K ratio of about 1:0.22:0.58. Considering the grain of spring wheat and spring barley forms, remarkably the highest share of protein nitrogen in total nitrogen was recorded at the lower sulphur dose and the largest N:P:K ratio. The sulphur application as well as broadening the N:P:K ratio resulted in a significant decrease in total protein content in the cereal grain. A considerable positive effect of sulphur fertilization on the content of protein nitrogen and its percentage in the total nitrogen in winter wheat and spring barley grain, was confirmed in the field experiment.
The addition of sulphur to the environment the crops grew, resulted in a decrease in the total protein content in wheat grain, whereas it was determined by N:P:K:Mg ratio in oilseed rape seeds and barley grain. At lower proportion of phosphorus, potassium, and magnesium for plant fertilization, sulphur application was associated with higher total protein content. The sulphur fertilization generally improved the nitrogen metabolism in test plants, which was associated with a reduction in the content of mineral nitrogen forms. Regardless of other experimental factors, application of sulphur contributed to the increase in the content of its organic form and sulfates in most cases. The addition of sulphur into the plant growth medium resulted in a significant increase in fat and total glucosinolates contents, including their alkene forms, while reducing the indole glucosinolates contents in winter oilseed rape seeds. The sulphur fertilization and widened N:P:K:Mg ratio in winter oilseed rape seeds was associated with a remarkable increase in gluten content and a significant decrease in its spreadability.
Performing the pot and field experiment expanded knowledge with a new cognitive aspect referring the efficiency of sulfur application depending on nitrogen to phosphorus, potassium, and magnesium ratio applied during the plant fertilization. The study justified the necessity of plants treatment with sulfur regardless of their nutritional needs for the macroelement. It also made possible to determine the optimal level of sulfur fertilization in relation to the other fertilizer constituents. The studies thus tend to conclude that the effect of sulfur on the resulting yield along with its quality is determined by plant fertilizing using other nutrients with maintain their optimal N:P:K ratio and the appropriate plant supply with magnesium.