In this text we will address the results obtained in a study carried out in partnership with the Federal University of Lavras (UFLA), authored by Lima et al. (2023), where agronomic and environmental aspects were evaluated after the use of fertilizers composed of the organic matrix AZOGEL® from ILSA Brasil.

INTRODUCTION

            Promoting food security and maintaining sustainable production patterns are the main challenges facing global agriculture, which are the target of the United Nations Sustainable Development Goals (https://sdgs.un.org/goals). Globally, the expansion of agriculture occurs in a scenario of increasing demand for fertilizers and depletion of natural resources, which requires alternative and economically viable sources of nutrients, actions that sustain the circular economy (Velenturf et al., 2019). The use of industrial by-products in agriculture emerges as a strategy to reduce waste disposal into the environment, in addition to providing an alternative source of nutrients for plants and possibly reducing costs with the application of mineral fertilizers (Lima et al., 2010; Coelho et al., 2015).

            The reuse of leather-derived waste is a pressing issue within the circular economy and represents an important step towards the sustainability of the tanning industry (Chojnacka et al., 2021). Rawhide or treated leather waste can contain up to 10.5% of protein per dry weight, which can be hydrolyzed to obtain collagen as a raw material for the production of organic fertilizers or soil amendments (Nogueira et al., 2011; Oliveira-Longatti et al., 2017; Majee et al., 2021). The organic matrix of fertilizers containing the by-product of the intermediate tanning process (BPIPT) derived from the transformation of collagen from hides and skins is homogeneous.

            BPIPT can have high N contents (up to 140 g kg^-1 N by dry weight) and in combination with other nutrients can be used to produce smart fertilizers (Majee et al., 2021; Stefan et al., 2021). These products can complement or replace the application of mineral N fertilizers (e.g., urea), increase nutrient use efficiency (NUE) (Nogueira et al., 2011; Ciavatta et al., 2012), increase N mineralization and microbial activity (Oliveira-Longatti et al., 2017), and lead to increased biomass and crop yield (Lima et al., 2010; Coelho et al., 2015; Majee et al., 2021).

            Given the importance of using fertilizers produced with a by-product of the intermediate tanning process, the work aimed to:

• Evaluate the chemical and biological properties of the soil after the application of organomineral fertilizers formulated with the AZOGEL ® matrix;
• To evaluate the impacts of such products on wheat growth and nutrition.

  Note: It is important to note that this trial was conducted for regulatory purposes and the results presented here were adapted from the original in order to demonstrate the effect of the organic matrix AZOGEL ® on the parameters mentioned above.

MATERIAL AND METHODS

            Soil samples were collected from the 0–0.2 m layer of a native area (native Cerrado vegetation) located in the Campo das Vertentes region, Minas Gerais, Brazil. According to the Brazilian Soil Classification System (Santos et al., 2018), soils were classified as typical dystrophic Red-Yellow Latosol (LVAd) and typical dystrophic Red Latosol (LVd), corresponding to Latosol in the USDA Soil Taxonomy (Soil Survey Team, 2014). Physical and chemical properties were determined in air-dry fine earth (ADFE; <2 mm) (Table 1).

            Soil samples were dried, crushed, and passed through a 4-mm sieve tube. Then, the samples were homogenized and stored in plastic bags. A mixture of calcium (Ca) and magnesium (Mg) carbonates in a molar ratio of 3:1 (Ca:Mg) was used to increase soil pH and base saturation to 60%, in agreement with previous soil analyses (Álvarez and Ribeiro, 1999). The soil was incubated at room temperature for 60 days with soil moisture maintained at field capacity. Soil samples were homogenized once a week during the incubation period. At the end of the 60 days, the mean pH values for LVAd and LVd were 6.15 ± 0.08 and 6.23 ± 0.06, respectively.

Table 1 – Chemical and physical characterization of the typical dystrophic Red-Yellow Latosol (LVAd) and the typical dystrophic Red Latosol Latosol (LVd) used in the experiments.

The experiments were conducted in two sequential stages:

1) incubation of fertilizers in soil samples for 30 days; and

2) wheat cultivation (Triticum aestivum L.) after incubation of fertilizers for 30 days.

Two experiments were conducted, one in each soil (LVAd and LVd), with the same completely randomized design, with five treatments and five replicates. The treatments consisted of the composition of two types of organomineral fertilizers (OMF), which contained mineral fertilizers based on nitrogen (N), phosphorus and potassium (NPK fertilizer), with and without the addition of S.

The organic matrix of the organomineral fertilizer (OMF) was BPIPT (byproduct of the intermediate tanning process). The treatments were identified as OM-IPT (BPIPT-based OM), OM IPT+S (BPIPT-based OM plus Sulfur (S)). Table 2 describes the composition and nutrient content of each OMF.

All fertilizers were oven-dried (40°C) and ground in a ball mill before their characterization and application to the soil. They were then passed through a 1 mm sieve to standardize the fertilizer granulometry and quartered in a stainless steel sampler. The FOMs were characterized according to the Manual of Official Analytical Methods for Fertilizers and Correctives (Brazil, Ministry of Agriculture, Livestock and Food Supply – MAPA, 2017).

TABLE 2 – Description of treatments used in the experiment.

The application of macronutrients (N, P, K and S) was based on the fertilization recommendation proposed by Malavolta (1980), with modifications to meet the objectives of this study, i.e., micronutrients were not added, which were already included in the source FOM, and the S doses varied with the treatments. The sources of inorganic fertilizers (commercial sources) used to supply N, P and K were, respectively, urea, monoammonium phosphate (MAP) and potassium chloride (KCl). No micronutrients were applied.

Incubation of FOM in soils (1st stage)

The first stage of the experiment was the incubation of FOM in the soils for a period of 30 days. The objective of this stage was to evaluate the interaction between FOM and the soils, assessing the levels of nutrients available after incubation and the effect on the soil microbiota.

• to FOM Incubation: Elements Available in Soils
• Availability of Cr, Cu, Pb, Zn, P and K after FOM incubation in soils was determined by the Mehlich-1 method (Mehlich, 1953).
• FOM incubation: microbiological attributes in soils

Microbial biomass carbon (MBC, µg C g-1) was determined by the methodology of (Islam and Weil, 1998). The metabolic activity of soil microbiota at the community level was measured by basal respiration (SBR, µg CO2 g-1 72 h-1) (Alef, 1995).

The activities of the b-glycosidase (µg r-nitrophenol g-1 h-1) (EC 3.2.1.21) (Eivazi and Tabatabai, 1988) and arylsulfatase enzymes (µg r-nitrophenol g-1 h-1) (EC 3.1.6.1) (Tabatabai and Bremner, 1970) were measured by optical density difference using a spectrophotometer (Micronal® Model B582). Total soil enzyme activity (TDA) was estimated by hydrolysis of fluorescein diacetate (TDA, mg fluorescein g-1 24 h-1) (Dick, 2011).

FOM incubation and wheat cultivation (2nd stage)

The second stage of the experiment was to evaluate plant growth in soil after FOM incubation. Ten wheat seeds (Triticum aestivum L. cultivar TBIO Aton) were sown in pots with 800 g of soil after FOM incubation. Daily irrigations were performed to maintain soil moisture at field capacity. After seven days, the seedlings were thinned to only seven plants per pot. The experiment was conducted for 30 days in a greenhouse, with controlled temperature and air humidity. The plant material was dried in an oven (60°C) until constant weight (after ± 72 h), and the dry mass of roots and shoots was weighed and recorded.

• FOM incubation and wheat cultivation: ADF (total soil enzyme activity) and b-glucosidase activity in soil.

The activity of the enzyme b-glucosidase (EC 3.2.1.21) (Eivazi and Tabatabai, 1988) and the estimate of the total enzymatic activity of the soil were obtained through the hydrolysis of fluorescein diacetate (FDA) (Dick, 2011).

• FOM incubation and wheat cultivation: soil pH.

The pH in H₂O and CaCl₂ was measured using a soil:solution ratio of 1:2.5 (v/v) (Tecnal TEC-11 pH meter) in soil samples after FOM incubation and wheat cultivation for 30 days.

• FOM incubation and wheat cultivation: total elemental composition of soils.

The total elemental composition of the soil samples at the end of the two experiments (incubation and agronomic efficiency) was obtained by portable X-ray fluorescence spectrometry (pXRF) following the recommendations described by Weindorf and Chakraborty (2020) and the USEPA 6200 method (USEPA, 2007).

Statistical analysis was performed using the R programming language (R Development Core Team, 2020), version 4.0.3. Normality and homoscedasticity of the data were assessed. Analysis of variance (p ÿ 0.05) was used to verify the significance of the treatments. Then, the treatments were compared using the Tukey HSD test with the emmeans package v1.4 (Length, 2020). Principal component analysis (PCA) was performed using the Vegan package v2.5-7 (Oksanen et al., 2016) to demonstrate the importance of the variables in explaining the nutrient content and biomass increase of wheat plants.

RESULTS

1st Stage

The P and K contents increased in both soils after FOM application (Figure 1). It was possible to note that this greater availability of elements – nutrients – was beneficial for wheat development and soil biological activity. Fertilizers based on tannery byproducts have shown many benefits to soil attributes and plant production. They present increased C and N contents in their composition (Ciavatta et al., 2012; Majee et al., 2021) and gradual release of N (Lima et al., 2010), which optimizes the use of nitrogen fertilizers by crops. This greater efficiency in N use can result in higher yields (Castilhos et al., 2002; Coelho et al., 2015) and lower soil acidity (Ferreira et al., 2003; Teixeira et al., 2006). Thus, the use of BPIPT for the production of FOM favors a circular economy (Chojnacka et al., 2021), as the by-product is incorporated into a different productive sector, that is, from the tanning industry to agriculture.

Figure 1 – P and K contents extracted by Mehlich-1 in typical dystrophic Red-Yellow Latosol (LVAd) and typical dystrophic Red Latosol (LVd) after incubation of FOM containing the AZOGEL ® matrix (mean ± SE, n = 5).

Microbial biomass carbon (MBC) increased with the addition of OMF, which reflects greater soil biological activity (Figure 2). With the addition of OMF, it was possible to observe that there were increases in the availability of resources, carbon, and nutrients for the microbiota, which favored the increase in MBC and microbial activities, even in a short experimental period. This effect was probably due to the increased availability of nutrients and energy for the microbial community in this soil. Tannery by-products are rich in proteins and lipids, which represent a promising source of nutrients, as they can stimulate the decomposition and mineralization activities of the soil heterotrophic community, providing nutrients for plants and microorganisms (Majee et al., 2021). What makes the reuse of this residue an environmentally friendly activity is that, in addition to disseminating the concept of circular economy in the industry (Velenturf et al., 2019), it is also a source of multi-element fertilizers for plants and microorganisms.

Figure 2 – Microbial biomass carbon (MBC) in a typical dystrophic Red-Yellow Latosol (LVAd – A, B and C) and a typical dystrophic Red Latosol (LVd – D, E and F) after incubation of FOM containing the AZOGEL ® matrix (mean ± SE, n = 5).

The FDA analysis better reflected the effects of FOM application in both soil types, while the enzyme β – glycosidase and arylsulfatase showed variable behaviors (Figure 3). The application of FOM led to higher wheat yields and increased enzymatic activities in the soil. However, the activity of the arylsulfatase enzyme decreased after the application of FOM in the LVd (Figure 3), which may be related to a greater availability of S after the application of the products. This enzyme acts in some stages of the mineralization of organic S, and reductions in the activity of arylsulfatase may occur if inorganic S is present in these fertilizers. Oliveira Longatti et al. (2017) also observed increases in microbial biomass and in the activities of the enzymes b-glIcosidase and urease after the application of tannery byproducts in two tropical soils.

Figure 3 – General soil enzymatic activity (fluorescein diacetate hydrolysis – FDA), arylsulfatase and b-glucosidase in a typical dystrophic Red-Yellow Latosol (LVAd) and a typical dystrophic Red Latosol (LVd) after incubation of different organomineral fertilizers containing the organic matrix AZOGEL (mean ± SE, n = 5).

2nd Stage

After wheat planting, treatments with FOMs that have collagen as raw material (ILSA) showed higher total enzymatic activity and higher activity of the b-glucosidase enzyme. The b-glucosidase and ADF activities were evaluated before and after wheat cultivation (Figure 4). These enzymes were very sensitive in the evaluation of soil microbiological activity in the incubation phase and in plant development after FOM application. Both soils showed a tendency for increased b-glucosidase and ADF activities after FOM application and higher wheat yields.

Figure 4 – General soil enzymatic activity (fluorescein diacetate hydrolysis – FDA) and b-glucosidase in typical dystrophic Red-Yellow Latosol (LVAd) and typical dystrophic Red Latosol (LVd) soils after wheat cultivation with organomineral fertilizers containing the organic matrix AZOGEL ® (mean ± SE, n = 5).

After planting wheat, treatments with FOM showed greater aerial part (SDM) and root (RDM) weight (Figure 6).

Figure 5 – Dry mass of aerial part (SDM), MSD and dry mass of root (RDM) of wheat in typical dystrophic Red-Yellow Latosol (LVAd) and typical dystrophic Red Latosol (LVd) after wheat cultivation with organomineral fertilizers containing the organic matrix AZOGEL ® (mean ± SE, n = 5).

The nutritional increase of macronutrients and micronutrients in the two types of soils used can be observed in figures 6 and 7. In wheat grown in LVAd, the P and K contents in SDM increased significantly in all treatments compared to the control. However, no difference was observed between FOM treatments. The Ca and Mg contents did not differ from the control. The SDM content was the highest for OM-ITP+S (3 g kg^-1) and the lowest for the control (1.8 g kg^-1).

Overall, the application of FOM in LVAd increased micronutrient contents. Specifically, Mn had an average content of 36 mg kg^-1 in the control, and an average content of 225 mg kg^-1 for FOM treatments in LVAd. Overall, micronutrient contents in SDM increased after FOM addition. However, probably due to the buffering effect of the higher clay content of this soil, the increases in Mn and Zn contents were less pronounced when compared with LVAd.

Figure 6 – Macronutrient and micronutrient contents in typical dystrophic Red-Yellow Latosol (LVAd).

Figure 7 – Macronutrient and micronutrient contents in typical dystrophic Red Latosol (LVd).

CONCLUSIONS

The application of organomineral fertilizer (FOM) in the soils of the present study increased the growth, macro (P, K, Ca, Mg and S) and micronutrient (Cu, Fe, Mn, B, Zn) contents in wheat plants.

This trend was more evident in the dystrophic Red-Yellow Latosol (LVAd), which presented lower clay and Fe oxide contents than the dystrophic Red Latosol (LVd) and, therefore, may be more responsive to changes in management practices. After wheat cultivation, the presence of S in the FOM led to soil acidification.

Furthermore, the application of organomineral fertilizer (OMF) increases microbial biomass carbon (MBC) with increased addition of OMF, which reflects greater soil biological activity. With the addition of OMF, it was possible to observe that there were increases in the availability of resources, carbon and nutrients for the microbiota, which favored the increase in MBC and microbial activities.

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Authors

• Agr Eng. Dr. Angélica Schmitz Heinzen
• Agricultural Eng. Msc. Carolina Custodio Pinto
• Agricultural Eng. Msc. Thiago Stella de Freitas