The aims of the study were to analyse the concentration of nitrate and ammonium ions in soil solutions obtained using MacroRhizon miniaturized composite suction cups under field conditions and to determine potential nitrogen leaching from soil fertilized with three types of fertilizers (standard urea, slow-release urea, and ammonium nitrate) at the doses of 90 and 180 kg ha⁻¹, applied once or divided into two rates. During a 3-year growing experiment with sugar sorghum, the concentration of nitrate and ammonium ions in soil solutions was the highest with standard urea fertilization and the lowest in variants fertilized with slow-release urea for most of the months of the growing season. Higher concentrations of both nitrogen forms were noted at the fertilizer dose of 180 kg ha⁻¹. One-time fertilization, at both doses, resulted in higher nitrate concentrations in June and July, while dividing the dose into two rates resulted in higher nitrate concentrations between August and November. The highest potential for nitrate leaching during the growing season was in July. The tests confirmed that the miniaturized suction cups MacroRhizon are highly useful for routine monitoring the concentration of nitrate and ammonium ions in soil solutions under field conditions.

Phosphorus (P) is a limited yet essential resource. P cannot be replaced, but it can be recovered from waste. We proposed the TRIZ approach (Teoria reszenija izobretatielskich zadacz - Rus., Theory of Inventive Problem Solving - Eng.) to identify a feasible solution. We aimed at minimizing the environmental impact and, by eliminating contradictions, proposed viable technical solutions. P recovery can be more sustainable based on circular economy and 4Rs (reduction, recovery, reuse, and recycling). The TRIZ approach identified sewage sludge (SS) as waste with a large potential for P recovery (up to 90%). Successful selection and application of SS management and P recovery require a transdisciplinary approach to overcome the various socio-economic, environmental, technical, and legal aspects. The review provides an understanding of principles that must be taken to improve understanding of the whole process of P recovery from wastewater while building on the last two decades of research.

The wastewater treatment process generates large amounts of P-rich organic waste (sewage sludge (SS)). The direct application of SS in agriculture, being controversial, is gradually being replaced by incineration, leading to the concentration of both P and heavy metals in the solid residual-sewage sludge ash (SSA). The novel closed-loop, cradle-to-cradle (C2C) approach leads to maintaining P production at current levels and counteracts its depletion in the future. The aim of this review is the presentation of the implementation of the C2C approach for P recovery. The paper focuses on steps that comprise P C2C, starting from the SS properties, being a derivative of wastewater type and treatment processes, to SS pre-treatment and finally leading to certified P-fertilizers production from SSA by application thermochemical or wet chemical extraction technologies. Examples of SSA treatment technologies and the final products are provided. It has been summarized that future research should focus on the production of SSA-based fertilizers aligning with the C2C concept and determining its effect on the various agriculture and horticulture crops.

In 2015–2017, field experiments were conducted, in two facilities of the Wroclaw University of Environmental and Life Sciences: at the Research and Didactic Station in Psary (51°19′08” N, 17°03′37” E) and in the plots of the Department of Crop Production in Pawlowice (51°17′32” N, 17°11′72” E). The research aimed to evaluate fresh biomass yield and selected quality parameters of quinoa grown as a green leafy vegetable. The study was conducted on two soils: medium (clay soil texture) and light (sand soil texture), sowing quinoa in spring and summer periods. On both soils, quinoa was harvested 5 times at each sowing date. The yields of fresh plant biomass, basic morphological characteristics and certain quality traits were compared. All experimental factors had a significant effect on quinoa fresh biomass yield. On light soil, quinoa yielded 4 times lower than on medium soil, and its cultivation posed a high risk, especially at the summer sowing date. The experimental factors used had the greatest effect on macronutrient content. Growing quinoa on medium soil yielded biomass with higher K, Mg, Ca and N-NO₃ concentration, while spring sown plants had higher K and N-NO₃ concentration. Harvesting date had the greatest effect on the change in nutritional values. Potassium content decreased as the harvest date was delayed, and N-NO₃ content decreased gradually until the fourth harvest date. The results showed that quinoa should be harvested as a green leafy vegetable when it reaches a height of 20–30 cm; biomass production is then at 500–1000 g per m², potassium content is less than 10 g per 100 g dry matter and N-NO₃ content is less than 100 mg 100⁻¹ f.m.