Nina Toth

Effects of organic and mineral fertilization on NPK status in soil and plant, and yield of red beet ( Beta vulgaris var. conditiva )

Two-year field fertilization trial with red beet (Beta vulgaris var. conditiva) was carried out at two locations in Croatia. The trial was set up according to the Latin square method with four fertilization treatments (5 kg m-2 stable manure, 50 and 100 g m-2 NPK 5-20-30 and unfertilized control). In most cases the highest soil P and K content was obtained in the treatment with stable manure or 100 g m-2 NPK 5-20-30. A similar situation as in the soil was also obtained in plants. The highest N, P, K contents in 2003, and also P and K in 2004 in red beet were determined in the treatment with stable manure. Comparison of yields per fertilization treatment shows that the control treatment gave the lowest yield in both years. The highest yield in 2003 was determined in the treatment with stable manure (0.99 kg m-2) and there was no significant difference in comparison with the 100 g m-2 NPK treatment (0.82 kg m-2). Although there were no significant differences in 2004 between fertilization treatments, the relatively highest yield (4.59 kg m-2) was determined in the treatment with 100 g m-2 NPK. Such wide variations are probably a consequence of weather conditions.

Influence of potassium fertilisation on the levels of phenolic compounds in sweet potato (Ipomoea batatas L.) leaves

Summary The nutritional value of sweet potato leaves (Ipomoea batatas L.) has recently been emphasised as their anti-oxidant and phenolic compounds can improve human health and provide nutritional benefits. This has increased the interest of the food industry and of consumers in using sweet potato greens as a functional food. To increase the level of phenolic compounds in sweet potato leaves, we studied the influence of potassium (K)-fertilisation at different N:K ratios [namely 1:1 (control), 1:2.5, or 1:5] on the phenolics contents and corresponding anti-oxidant activities of two cultivars of sweet potato, ‘Bat1’and ‘Boniato’. In general, enhanced K-fertilisation increased the level of phenolic compounds and the corresponding anti-oxidant activity. However, the two cultivars differed in their response to K-fertilisation. Phenolic acids were increased (by approx. 20%) in ‘Bat1’ only after the application of N:K at a ratio of 1:5, while K-fertilisation at all rates increased the flavonoid contents of both cultivars (by approx. 300%). Our results could be useful for sweet potato producers who wish to make informed decisions on which cultivar and/or mineral fertiliser regime to choose in order to produce sweet potato leaves of the desired nutritional quality.

Status of Fe, Mn and Zn in red beet due to fertilization and environment

Soil is a non-renewable resource, so it should be taken care of it. High quality food with sufficient yield for a growing human population can be produced only if plant nutrients are added to the soil by fertilizers to increase soil fertility, but the fertilizers have to be used economically, with the aim of raising the nutrient content available in the soil in order to meet plants’ needs. The goal of the present investigation was to determine the effect of application of organic and mineral fertilizers as well as the effect of research environment on micronutrient content in red beet root. A field trial (2003–2005) was set up in a hilly part of Croatia according to the Latin square method, with four types of fertilization (control, 50 t stable manure*ha-1, 500 and 1,000 kg NPK 5-20-30*ha-1). After digestion of plant material with concentrated HNO3, iron, manganese, and zinc were determined by an atomic absorption spectrophotometer (AAS). The highest average red beet root micronutrient contents (270 mg Fe*kg-1 in dry matter, 96 mg Zn*kg-1 in dry matter, and 53 mg Mn*kg-1 in dry matter) were determined in the first research environment (Brasljevica in 2003) with low potassium soil content. There was a general decreasing trend in contents of the studied micronutrients (Fe, Mn and Zn) with NPK 5-20-30 fertilization (and by application of high doses of potassium), certainly due to antagonistic activity with potassium. It is suggested to fertilize with both 500 kg NPK 5-20-30*ha-1 and microelement fertilizers.

REUSE OF LEACHED NUTRIENT SOLUTION IN TOMATO SOILLESS CULTURE

The advantage of closed soilless systems is protection of surface and ground water from pollution with nutrients and pesticides. Beside that, savings of water and nutrients could be made. The aim of the research was to determine amounts of added and leached nutrient solution during tomato growing period, their composition and possibility of reusing leached nutrient solution for fertigation after filtration and UV-sterilization. Tomato plants were planted on 11th February. During the harvest period from 12th May till 27th October 39.1 kg m-2 of marketable fruits were harvested. Number and duration of fertigation rates depended on the plant development stage and weather conditions. Amounts of leached nutrient solution were measured with installed percolate collectors. Leached nutrient solution was collected, filtered and UV-sterilized. After sterilization it was mixed with a new nutrient solution in a 1:3 ratio. Composition of nutrient solution was determined periodically (every two weeks) at the laboratory, while pH- and EC-values were measured with a portable pH- and EC-meter once a week. During growing period 919 L m-2 nutrient solution was added and 371 L m-2 was leached. The ratio between added and leached nutrient solution ranged from 18.7 % to 55.4 %. For all macro elements, with the exception of phosphate, higher concentrations (from 43 % for K+ to 101 % for Mg2+) were recorded in leached than in added nutrient solution. Phosphate concentration was 58 % lower in leached than in added nutrient solution. Reuse of leached and sterilized nutrient solution is feasible but requires constant control of the composition and pH- and EC-values of nutrient solution to avoid higher deviations, which might have a negative effect on tomato yield. Closed soilless system is ecologically acceptable because excess nutrient solution is adequately disposed of and reused in the production cycle.