Two protein-hydrolyzate-based fertilizers (PHFs), one from alfalfa (AH) and one from meat flour (MFH), were studied chemically and biologically. AH and MFH revealed a different degree of hydrolysis and a different amino acid composition. The biostimulant activity was investigated using two specific and sensitive bioassays of auxins and gibberellins. Extracts of AH and MFH elicited a gibberellin-like activity and a weak auxin-like one. To improve our understanding of the biostimulant activity, AH and MFH were supplied to maize plants and their effect on growth and nitrate metabolism was studied. Both PHFs increased root and leaf growth and induced morphological changes in root architecture. Besides, the treatments increased nitrate reductase (NR) and glutamine synthetase (GS) activities, suggesting a positive role of the two hydrolyzates in the induction of nitrate conversion into organic nitrogen. Moreover, treatments enhanced GS1 and GS2 isoforms in maize leaves. The latter isoform, amounting to 5- to 7-fold the level of the former, appears to be a superior form in the assimilation of ammonia. The high NR and GS activities together with the high induction of GS isoforms indicate a stimulatory effect of the two PHFs on the assimilation of nitrate. In addition, a role of amino acids and small peptides of the two PHFs is suggested in the regulation of the hormone-like activity and nitrogen pathway

Intensive land use may affect soil properties (e.g., decreased soil organic matter [SOM] content) and, consequently, reduce crop yields considerably. One way of counteracting the loss of SOM and stimulating plant productivity could be the use of organic residues from agro‐industrial processes as bioactive products. The present study was focused on the possible effects of phenol‐containing organic substances derived from agro‐industrial by‐products on maize (Zea mays L.) metabolism in a pot experiment. Plants were grown for 12 d in a nutrient solution in the absence (control) or in the presence of either a cellulosolitic dry apple hydrolyzate (AP) or a dry blueberry cool extract (BB) applied at two rates (0.1 and 1 mL L–1). Both products increased root and leaf biomass and led to higher concentrations of macronutrients in the plant tissue. AP and BB also had a positive impact on nitrogen (N) metabolism stimulating the activity and gene expression of phenylalanine ammonia‐lyase, a key enzyme of the phenylpropanoid pathway. Furthermore, both products increased leaf concentrations of phenols (+ 28% and 49% for AP and BB, respectively) and flavonoids (+ 22% and 25% for AP and BB, respectively). From our results it can be assumed that residues from agro‐industry may be successfully used as bioactive products in agriculture to increase plant yield and resistance to stress conditions.

Traditional agricultural production systems are evolving towards organic, sustainable, or environmentally friendly systems. Nonetheless, it is important to maintain crop yield and quality. For this purpose, the use of peptide‐based products from animal sources in agriculture could be a way to both reduce the disposal of animal‐processing residues and decrease the use of mineral fertilizers. The aim of our work was to obtain new insights into the biological effects of meat hydrolyzate (MH) derived from the hydrolysis of tanning residues. Maize (Zea mays L.) was grown hydroponically in a climatic chamber, and 12‐d‐old plants were treated for 48 h with different concentrations of the MH: 0 (control), 0.01 or 0.1 mL L–1. Both treatments enhanced plant growth and microelement concentrations in maize seedlings and decreased NO$ _3^- $, PO$ _4^{3-} $, and SO$ _4^{2-} $ concentrations compared to the control. The faster metabolic conversion of these ions was due to enzyme activities of nitrogen (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and aspartate aminotransferase) and carbon metabolism (malate dehydrogenase, isocitrate dehydrogenase, and citrate synthase). The gene transcription for these enzymes was in line with their activities. The effects of MH could partly be ascribed to endogenous indole‐3‐acetic acid and partly to amino acids and small peptides detected in the tested compound. This study shows that tanning‐process residues can be recycled and used in agriculture.

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Mineral phosphorus (P) fertilization in calcareous soils is not efficient enough to ensure optimal plant growth. Therefore, a higher P input is generally needed. Polymer-coated fertilizers are a promising fertilizer category that seems to affect soil extractable P, thus permitting a reduction in fertilizer rates. We tested this hypothesis in a short-term (45 days) field trial by evaluating both the agronomic and the environmental implications. In this study, two conventional fertilizers (single superphosphate, SSP; mono-ammonium phosphate, MAP) and a slow P-release fertilizer (polymer-coated MAP, PCMAP) were tested for their effects on soil P pools by combining different P rates and degrees of coating. The P soil test was determined with either Olsen or Mehlich-3 solution (available P), whereas the P soil release was estimated through water extraction. The efficiency of fertilizers was evaluated by assessing the growth of Hypericum × moserianum (L.) plants. As expected, both SSP and MAP influenced the soil Mehlich-3-P, Olsen-P, and water-P, as concentrations increased with the fertilizer rate. Conversely, PCMAP decreased the soil extractable P with increasing coating. The plant dry weight and P uptake linearly correlated with the fertilizer rate for SSP and MAP, whilst they achieved the maximum yield with PCMAP. This result indicates the underdosing for conventional fertilizers. With reference to the soil test P with water-P, the presence of change points showed low water-P release concentrations for PCMAP and SSP, and high water-P release for MAP. In conclusion, in the short-term period both soil extractable P and water-P depend on the type of fertilizer, whereas the amount of added P has rather a secondary role. PCMAP, in particular, ensures high plant P use efficiency with minimum environmental impacts.