The potential of keratin wastes originating from poultry farms in practical application as a valuable organic fertilizer, gives rise to the need for intensive study on their effect on plants. In this study, for the first time there has been examined the influence of hen feather keratin bio-hydrolysate (FKH) and hen feather keratin compost (FKC) on plant growth, and the following features that indicate the plant condition: the leaf chlorophyll content, the activity of phenylalanine ammonia lyase (PAL) and guaiacol peroxidase (GPX) enzymes. The results of pot experiments showed a potential plant growth promoting effect of FKH, applied as a leaf treatment and of FKC manure. Fertilization of tested plants with FKC resulted in significant increase of their fresh weight. There was no effect on plant biomass after FKH treatment. The stimulating effect on plant physiology was expressed by decreased PAL activity after FKC treatment, and enhanced GPX activity, after FKH and FKC treatment. The application of FKC as a manure gave better effects for the plant condition expressed by the activity of PAL and GPX in comparison with FKH spraying. The chlorophyll content did not prove to be an efficient parameter to evaluate the impact of FKH or FKC on white cabbage, tomato, and maize plant. However, a significant increase in the leaf chlorophyll a, b, and a+b concentration was observed in cucumber plant after FKC treatment. Among the tested plants, the cucumber has shown the most profitable effect of feather compost on plant growth.

This paper focuses on the agronomic evaluation of a synthetic NPK (N in the form of urea, P and K in the form of phosphate monopotassium) fertilizers blended with four types of pine (Pinus sylvestris L.) wood biochar prepared at different thermal regimes (300 °C, 400 °C, 600 °C and 700 °C). The evaluation of benefits was done based on crop nutritional status and soil fertility. The pot experiment was set up with fertile Haplic Luvisol fertilized with 1.85 g kg⁻¹ of blends of biochar (1.25 g) with urea (310 mg) and KH₂PO₄ (290 mg), which is equivalent to 500 kg ha⁻¹ (biochar ~67.6%; N ~7.8%; P ~3.6%; K ~4.7%) applied before sowing. Only NPK blends made with biochar containing 75% or 85% carbon increased the biomass of 27-day old wheat seedlings from 12% to 20% in comparison to NPK applied alone. These blends raised the content of Mn and Fe in plants but decreased the contents of Ca and Mg. All the tested mixtures enhanced soil fertility by increasing the content of humic acids. Additionally, the content of potentially phytotoxic phenolic compounds was lower. In general, the addition of biochar to NPK fertilizer did not show a negative effect on crop quality. The overall results of the study suggest that the application of low doses of biochar to synthetic fertilizer can benefit crops and can support soil fertility.