Phosphorus and Potassium Cycling, Biological Nitrogen Fixation in Soybean, and Soil Microbial Activity in an Oxisol Fertilized with Wastewater from Heparin Production

Applying industrial waste to soil is one way of closing and linking productive cycles; however, industrial waste often contains pollutants such as salts, heavy metals, or toxic compounds with potentially adverse effects on soil health. The aim of this work was to assess the effects of industrial saline wastewater (ISW) from heparin production as a biobased fertilizer on soil nutrient phytoavailability, soybean development, biological nitrogen fixation, and soil microbial activity in an Oxisol. Five ISW rates (0, 10, 20, 40, and 60 m(3) ha(-1)) were used in experiments under controlled conditions with soybean for 146 days and soil incubation experiments for 47 days. ISW had no negative impact on leaf chlorophyll content, number or dry mass in root nodules, or dry mass in soybean plants. Soil P, K, and Na contents were immediately increased upon ISW application but fell to their initial levels with time (especially those of P and Na). However, plants fertilized with ISW rates above 20 m(3) ha(-1) produced significantly more pods (31%) and grains (21%), and had greater thousand weight grain and yield (up to 25%), on average than unfertilized plants. By contrast, low ISW rates had no significant effect on ureide content (N biologically fixed). The highest ISW rate (60 m(3) ha(-1)) decreased ureide levels by up to 60% relative to no ISW application. ISW boosted soil microbial activity in proportion to its rate; also, it increased organic carbon availability for soil microorganisms irrespective of rate. ISW from heparin production is thus a potentially effective biobased fertilizer use of which at 20-40 m(3) ha(-1) in humid areas is recommended to reduce the amounts of synthetic fertilizers needed, and improve soil nutrient availability and soil microbial activity, all without adversely affecting soil health or biological N fixation.