Long-Term Integrated Crop–Livestock–Forestry Systems Recover the Structural Quality of Ultisol Soil

Abstract

Integrated Crop–Livestock–Forestry Systems (ICLFS) offer stakeholders sustainable options to produce goods and services. Those additionally manifest as enablers of environmental conservation of soil functioning. We, therefore, analyzed the quality of Ultisol for physical and chemical properties under restorative or regenerative models of long-term (nine years) ICLFS. The arrangements comprised integrated Crop–Livestock; integrated Crop-Livestock-Forestry, integrated Crop–Livestock–Forestry with a single or triplicate rows of Eucalyptus; and Eucalyptus plantation, natural vegetation, and bare soil with resurgence of grasses (reference). We collected samples of soil at 0.05, 0.05–0.1, and 0.1–0.2 m depths throughout the areas to quantify standard properties, including water infiltration, hydraulic conductivity, degree of flocculation, mechanical resistance to penetration, stability of aggregates, physical fractioning of organic matter, and fertility. We applied principal component analysis to analytical data to calculate accurate discriminant variables to distinguish systems by structural quality. We obtained evidence for the crop–livestock framework improving physical and chemical properties; hence, this intervention outperformed others in developing environmental restoration. Additionally, as the reference consisted of comparable properties to those in integrative systems and native vegetation, it supported the ability of the soil to gradually recover itself over time. Therefore, our study provides knowledge to advance the field’s prominence in implementing ICLFS for the environmental reclamation of the condition or process degrading the soil and its functions for sustainable agricultural production.

1. Introduction

Brazil is the top country for meat exports worldwide. As of 2020, its contribution to the global beef market was 2.2 million tons. Brazil’s herd encompasses 217 million cattle. Pastures occur in 30.9% of the Brazilian territory, allowing stakeholders in its climate-positive livestock sector to produce beef cattle extensively, semi-intensively, or intensively [1]. However, as commercially active grasslands eventually manifest as unsustainable to producers and consumers, they drive the need to develop and implement alternatives [2], such as integrative crop–livestock–forestry systems (ICLFS), to address pressing social and environmental issues while promoting economic symmetry. Domestically, the area supporting models of ICLFS was 17,431.5 ha in 2020/21, representing a significant growth of 52% relative to 2015/16 [3].In Brazil, pastures are the most important basis of ruminant production; nonetheless, degradation of these areas through extensive livestock farming has made sustainable production impossible [4], promoting the degradation of water and soil [5]. The recovery of pastures and soil quality is carried out by reversing the degradation process with integrated systems [6].

As global demands for goods and services from agriculture increase intensively, they force full-scale farmers to expand their systems over natural landscapes to produce food, energy, and fiber cost-effectively [7]. Intensifying agricultural supply chains can provide a quantitatively sufficient output to secure the world population [7]; however, conditions or processes depleting natural resources, such as deforestation and topsoil running out, can occur when an economic framework is irrational, exceeding the ecological balance [7].

Experts in livestock from the Brazilian Agricultural Research Corporation (Embrapa) stressed at the Conference of the Parties (COP26), which brought countries for global climate summits, the significance of ICLFS in capturing carbon dioxide (CO₂) from the atmosphere. Those can store up to 2.05 Mg ha⁻¹ yr⁻¹ of the target greenhouse gas (GHG) at a 1 m depth in tropical soils [8,9,10,11,12]. Additionally, they can act as a sink to methane (CH₄); hence, they can be enablers of sustainable development by mitigating global warming and its effects on climate change [13].

Complementarily, ICLFS can offer possibilities to conserve biodiversity, reduce the anthropogenic depletion of natural resources and ecosystem services, and improve the soil’s quality for sustainable agricultural development [14,15]. Therefore, researchers emphasize analyzing them edaphically and climatically for standard physical and chemical indicators of stability and scalable functionality [16,17,18], such as hydraulic conductivity, organic matter fractioning, and fertility [19]. However, they often focus on conducting short-term studies and trials, making it challenging to determine the role of ICLFS in promoting or recovering soil’s properties and functions temporally and spatially.

Perhaps, we need a couple of years or even decades to provide accurate and reliable insights into the conceptual and technical ramifications of a stable arrangement within a realistic design. We, therefore, implemented models of ICLFS on an Ultisol under severe anthropogenic degradation for environmental restoration or regeneration in the long term. Nine years later, we analyzed them for their effectiveness in developing the soil’s structural quality.

2. Materials and Methods

2.1. Edaphoclimatic Conditions of the Study Area

We conducted our study in the division of agricultural production of APTA (São Paulo’s Agency for Agribusiness Technology), Andradina, northwest São Paulo, Brazil, near 20°55′ south and 51°23′ west. The regional climate is tropical; hence, it consists of a rainy summer and dry winter, with annual precipitation and temperature of 1150 mm and 23 °C, respectively. Precipitation distribution and mean temperatures in the experimental area from 2012 to 2022 were monitored and were as typically described for the region (Figure 1). Additionally, the soil throughout the experimental area is a dystrophic Ultisol [20]; its degree of slope is 6%, making it undulating.

2.2. Implementation of Integrative Crop–Livestock–Forestry Systems

2.2.1. A Brief History of On-Site Anthropogenic Degradation

The unsuitable and unsustainable exploitation of the area for extensive grazing caused the soil to severe physical and chemical degradation over time and spatially, driving the need for environmental restoration. Therefore, such a medium initially consisted of 4.8 pH, 15 g dm⁻³ organic matter (OM), 3 mg dm⁻³ phosphorus (P), and 1.8, 7, 5, and 19 mmol_c dm⁻³ of K, Ca, Mg, and potential acidity, respectively; also, it texturally comprised 10.7, 11.3, and 78% of clay, silt, and sand, respectively [21]. Importantly, we selected a permanent protection area (27 ha) occurring underneath an on-site rainforest to refer to the native vegetation of Cerrado, which stands as a vast tropical savanna ecoregion of Brazil (Figure 2).

2.2.2. Conventional Tillage

We characterized the soil to establish a baseline for amendment and spatio-temporal comparative analysis. Therefore, we plowed and harrowed it mechanically for decompaction, thereby decreasing impedance for roots. We then applied 1200 kg ha⁻¹ limestone (80% neutralization power) to increase basis saturation from 42% to 70% while incorporating gypsum at 600 kg ha⁻¹ to provide sulfur (S) for crops. We ground our conventional preparation to the technical specifications of the strictest Brazilian institute for plant nutrition and fertilization [22].

2.2.3. Planting of Eucalyptus

We planted E. urograndis (E. grandis × E. urophylla) in October 2012 for integrated crop–livestock–forestry (

Table 1. Conditions of integrative systems for the environmental restoration of Ultisol’s properties.

Integrated System	Description	Legume
Crop–livestock–forestry	Corn, grass, and Eucalyptus (200 ind. ha−1; single lines × 17 m window)	Yes
	Corn, grass, and Eucalyptus (500 ind. ha−1; triplicate lines × 21 m window)
Crop–livestock	Corn and grass
Plantation	Artificial forest of Eucalyptus	No crop
Native vegetation	Permanent protection spot under a typical rainforest of Cerrado
Reference	Bare soil with natural resurgence of grasses and shrubs

). We, therefore, established such a commercially available hybrid clone in arrangements of 200 and 500 ind. ha⁻¹ to analyze whether the density of the forestry component can determine the ability of an integrative system to restore soil’s properties. We applied a suite of macro and micro minerals for fertilization on specific spots (and per hole) once at planting (8.4 g N, 63 g P₂O₅, and 33.6 g K₂O) and then twice after 4 (40 g urea, 9 g zinc sulfate, and 1.2 g boron) and 12 (160 g urea) months of the cultivation. Other practices included watering, weeding, and replanting.

2.2.4. Sowing of Soybean

We introduced soybean (Glycine max cv. BMX Potencia) into systems with and without Eucalyptus in December 2012 to boost integrated crop–livestock–forestry or crop–livestock. We, therefore, sowed it mechanically by operating a plantographic sower machine (SAM200, Semeato^®, São Cristovao, Passo Fundo, RS, Brazil) coupled to a tractor (TL 75 4 × 4, New Holland^®, Piracicaba, Brazil). The equipment precisely dropped 20 seeds per meter onto an arrangement of 4 lines 0.5 m apart; hence, the population density of such a starting agricultural component was 400,000 pl ha⁻¹. The quantities of N, P₂O₅, and K₂O for fertilization during seeding were 12, 90, and 48 kg ha⁻¹, respectively. We added 40 kg ha⁻¹ of P₂O₅ and K₂O to the field after 40 days of cultivation to allow the crop to overcome the poor fertility of the soil under degradation. After harvesting it, we sprayed glyphosate (Roundup WG) at 250 L ha⁻¹ on the area via a sprayer mounted on a tractor for desiccation. Importantly, we controlled weeds chemically by spraying 1240 g ha⁻¹ of a potassium salt of glyphosate (Zapp QI 620) at pre-emergence to avoid interspecific competition over resources available from the medium. We applied cobalt (0.22 g ha⁻¹) and molybdenum (2.25 g ha⁻¹) together with the pesticide to improve the biological fixation of N₂ by the legume, allowing it to produce and accumulate a significant quantity of straw on the field to implement a no-tillage successive crop–pasture system.

2.2.5. Intercropping Maize with Pasture

As of December 2013, we seeded maize (Zea mays cv. BG 7049) on legume straw from soybean for integrated crop–livestock within a non-tillage fashion. We, therefore, set the precision sowing equipment to distribute 8 kg ha⁻¹ of seeds on rows 0.8 m apart, yielding a population density of 62,500 ind. ha⁻¹. Its fertilization included 24.8, 86.8, and 49.6 kg ha⁻¹ of N, P₂O₅, and K₂O during seeding and 200 kg ha⁻¹ of urea after 20 days of growing. We then seeded palisade grass (Urochloa brizantha cv. Marandu) on narrower lines (0.2 m apart) within rows of maize for intercropping. After harvesting corn for silage in March 2014, we split the area into plots for mob grazing (i.e., short-duration, high-density grazing with an extended grass recovery period). Importantly, we treated maize by thoroughly mixing seeds with thiamethoxam (Cruiser 350) at 105 g of the active compound per 100 kg of the material to protect it against early-stage herbivore attacks.

2.3. Technical Assessment

In the years 2020 and 2022, we determined the long-term recuperative potential of integrative systems for standard physical and chemical properties (

Table 2. Physical and chemical indicators of the recuperative potential of integrative systems.

Variable	Unit	Instrument/Reference
Aggregate stability	%	Teixeira et al. [23]
Average aggregate diameter	mm	Teixeira et al. [23]
Water-dispersing clay	g kg−1	Teixeira et al. [23]
Gravimetric humidity	g g−1	Teixeira et al. [23]
Degree of flocculation	%	Teixeira et al. [23]
Fractioning of organic matter	Kg kg−1	Yeomans et al. [24]
Infiltration of water	mm h−1	Zang, R. [25]
Hydraulic conductivity	cm h−1	Naik et al. [26]
Resistance to penetration	MPa	Automatic digital penetrometer (TE096, Falker®, Porto Alegre, Brazil) [27]
Organic carbon	g kg−1	Yeomans et al. [24]
Clay	(%)	Teixeira et al. [23]
Silt	(%)	Teixeira et al. [23]
Sand	(%)	Teixeira et al. [23]
Phosphorus (P-resin)	mg dm−3	Raij et al. [28]
Potassium (K)	mmolc dm−3	Raij et al. [28]
Magnesium (Mg)	mmolc dm−3	Raij et al. [28]
Calcium (Ca)	mmolc dm−3	Raij et al. [28]
Organic matter (OM)	g dm−3	Raij et al. [28]
Aluminum (Al)	mmolc dm−3	Raij et al. [28]
Potential of hydrogen (pH)	Dimension less	Raij et al. [28]
Potential acidity (H + Al)	mmolc dm−3	Raij et al. [28]
Sum of bases (K + Ca + Mg)	mmolc dm−3	Raij et al. [28]
Cation exchange capacity	mmolc dm−3	Raij et al. [28]
Basis saturation	%	Raij et al. [28]

). We, therefore, randomly sampled the soil at layers of 0–0.05, 0.05–0.1, and 0.1–0.2 m depth throughout experimental areas (Figure 1) for routine laboratory analyses. We conducted them in triplicate.

2.4. Statistical Analysis

We compared integrative systems by post hoc Tukey’s honestly significant difference (HSD) test. We, additionally, applied a correlational analysis (Equation (1)) and principal component analysis (PCA) to datasets to calculate explanatory relationships between indicators of recuperative performance for a deeper understanding. We ran analyses in R software (R x64.4.1.0) for statistical computing and graphs [29].

$$r=\frac{N\sum xy-\left(\sum x\right)\left(\sum y\right)}{\acute{\sqrt{\left[N\sum x^2-{\left(\sum x\right)}^2\right]\left[N\sum y^2-{\left(\sum y\right)}^2\right]}}}$$

(1)

where r is the correlation coefficient, n is the number of pairs of scores, ∑xy is the sum of the products of paired scores, ∑x is the sum of x scores, ∑y is the sum of y scores, ∑x² is the sum of squared x scores, and ∑y² is the sum of squared y scores.

3. Results

3.1. The Impact of Integrative Systems on Ultisol’s Properties

By analyzing the outcome of Tukey’s test (Figure 3), we recognized a significant influence of integrative systems on Ultisol’s quality. We, therefore, determined their impact on chemical and physical properties as positive, irrespective of the sampling layer (Tables S1 and S2, Supplementary Material). The crop–livestock system brought the highest estimates of organic matter, Mg, gravimetric humidity, and infiltration into a spatio-temporal comparative analysis; hence, it outperformed integrated crop–livestock–forestry in replenishing fertility and restructuration. Such a combination of maize and palisade grass could develop a suite of variables–these above and implicit others (e.g., P-resin, potential acidity, and cation exchange capacity) as effectively as a native forest.

Therefore, comparatively, it can offer stakeholders the most reliable integrative solution to mitigate anthropogenic degradation in the long term. A crop–livestock–forestry association can also be an eco-friendly alternative for environmental reclamation since it developed comparable organic matter and gravimetric humidity to those of native vegetation underneath a typical rainforest of Cerrado without degradation.

The density of Eucalyptus cannot determine its recuperative potential. We introduced limestone into plots to improve acidity; however, we could not separate treatments upon either pH or Ca. Generally, our practical models for the long-term environmental recovery of degradation delivered a synergistic effect on Ultisol’s quality.

We, therefore, obtained better measures of its properties over time (Tables S1 and S2, Supplementary material). In integrated crop–livestock, for instance, organic matter increased from 14.7–21.3 to 16.7–24.7 g dm⁻³ (Table S1, Supplementary Materials), while the quantity of dispersive clay in water decreased from 19.11–45.92 to 12.56–39.75 g kg⁻¹ (Table S2, Supplementary Materials) between 2020 and 2022.

3.2. Correlational Analysis of Indicators of Recuperative Performance

We established functional relationships between chemical and physical properties (Figure 4). For instance, we calculated a significant Pearson’s r of 0.75 (p > 0.05) between organic matter and average aggregate diameter. Therefore, particles developed a higher diameter as the quantity of organic matter increased, supporting its positive contribution to binding functionality and, consequently, structuration. In contrast, average aggregate diameter and K brought a negative correlation (r = 0.95; p < 0.05) into the correlational modeling. Therefore, as the availability of K from the system increased either by fertilization or mineralization of leguminous straw, it produced particulates of lower dimension.

Potassium also established negative correlations with the degree of flocculation, gravimetric humidity, and organic matter, further supporting the conversion of vegetable cover to minerals and, more importantly, its antagonistic role in the structuration and dynamics of solutes, such as air and water. The degree of flocculation developed positive and negative correlations with aggregate stability and water-dispersing clay, respectively. Therefore, the lower the dispersive activity of clay, the less it flocculates, which is significant to infiltration and aeration since air and water move between and within aggregates. Additionally, plant roots grow better in a matrix where clayey clusters do not plug pores, thereby decreasing hydraulic flows, such as drainage. A negative correlation (r = 0.95; p < 0.05) between water-dispersing clay and infiltration of water supported the statement.

3.3. Insights into the Environmental Recovery of Ultisol’s Properties

We divided the high-dimensionality original datasets into insightful subsets, namely PCI and PCII (primary principal component (PCI); secondary principal component (PCII)) by orthogonalization. Therefore, such latent hits spanned 46.1 and 24.3% of the variance in information about 2020. As of 2022, they allowed for the explanation of 32.7 and 22.15% of the spatio-temporal variability, respectively (Table S3, Supplementary Materials).

By analyzing the outcome of PCA for 2020’s data (Figure 5), we assigned PCI and PCII for neutralization and rearrangement of particles, respectively. For instance, while the pH and basis saturation moved forward, potential acidity and saturation of Al moved backward in the analytical space of PC_I. Additionally, while the degree of flocculation, average aggregate diameter, and gravimetric humidity moved upward, the water-dispersive clay moved downward in the second dimension of the bi-plot map. These significant relationships between eigenvectors and eigenvalues supported the ability of integrative systems to recover Ultisol’s quality, especially the crop–livestock framework. Such a combination moved the farthest from the graphic origin in the first dimension of the factorial chart; hence, it provided the most reliable insight into the recovery of chemical properties by neutralization and, subsequently, alkalinization. It also provided a meaningful prospect for the rearrangement of structuring particles since its correlations with infiltration of water (r = 0.7, p < 0.05), hydraulic conductivity (r = 0.95, p < 0.05), and aggregate stability (0.85, p < 0.05) were positive.

An integrated crop–livestock–forestry with Eucalyptus within an arrangement of single lines could not contribute to significantly improving the chemical and physical properties of the soil as an integrated crop–livestock. By introducing such a forestry component at a higher density into an integrative system, we could develop its benefits to cation exchange capacity (r = 0.95, p < 0.05) and degree of flocculation (r = 0.9, p < 0.05). However, increasing litter near trees can intensify the occurrence of acid compounds by organic matter breakdown. As organic carbon and magnesium moved closer from the graphic origin of the bi-plot chart, we could not precisely and accurately map systems to either structuration or replenishment of nutrients until 2020. We achieved it only in 2022 (Figure 3).

By analyzing the outcome of PCA for 2022’s data (Figure 5), we could identify a restructuration of eigenvectors and eigenvalues. Therefore, conditions or processes of environmental recovery of Ultisol’s properties by integrative systems changed over time and spatially; hence, we reinterpreted PCI and PCII as structuration and replenishment of nutrients, respectively. For instance, integrated crop–livestock moved upward in the second dimension of the bi-plot map, establishing significant positive correlations with P-resin (r = 0.9, p < 0.05), Mg (r = 0.85, p < 0.05), and basis saturation (r = 0.7, p < 0.05). Therefore, its position and closer spatial synergistic connections with such discriminant eigenvectors in the northeast quadrant of the multivariate chart provided the most reliable insight into a series of improvements by structuration and replenishment of nutrients.

4. Discussion

We obtained evidence for integrative systems recovering the Ultisol’s quality. They significantly improved soil’s chemical and physical properties over time and spatially; hence, they allowed the growth of vegetable components while yielding valuable and scalable outcomes, such as edible grains (e.g., soybean and corn) for human nutrition, fodder (e.g., maize’s green foliage), and forage (e.g., palisade grass) for animal husbandry (cattle grazing). Although farm soil severely degraded the site during its implementation, our practical models for environmental restoration or recuperation reestablished its compositions and functions in the long term, making it capable of agricultural, livestock, or forestry production. Therefore, they could be at least comparable (integrated crop–livestock–forestry, irrespective of the density of Eucalyptus) to or even outperform (integrated crop–livestock) native vegetation (without anthropogenic intervention) in structure and fertility.

We emphasize that the soil under study has a sandy texture; thus, the discussion about a few studies carried out on integrated systems in sandy soil becomes relevant. The low organic carbon content is related to the high sand content in the soil [30], lower nutrient retention [31], and greater soil erosion [32]. However, integrated systems, when used properly, becomes efficient to recover degraded sandy soil [33]. Thus, integrated systems help water retention in sandy soil so that the fine roots of the tree component contribute to the increase in microporosity in the subsoil without interfering with macroporosity [34]. Studies in the regions of Northeast Paraná (Brazil), sandy soil that has a high erodibility rate and low water storage rate, producers are using integrated systems to increase crop productivity and provide ecosystem services [35].

Such a permanent protective spot under a typical rainforest of Cerrado generated and accumulated vegetable litter on topsoil, releasing significant quantities of organic (e.g., carbon) and inorganic (i.e., K, Ca, and Mg) compounds for autochthonous flora consisting of grasses, shrubs, and trees [36]. While integrative systems without a forestry component could not improve the soil’s quality by littering, they could produce similar properties to those under native vegetation by generating straw. Species of Urochloa spp. can add organic matter and N to the soil, making it an alternative to develop high-throughput integrative systems in tropical zones [37,38].

In addition, root branching can develop porosity for infiltration, drainage, and aeration; hence, it either balances or enhances the masses of water and gases [39], as evidenced by higher gravimetric humidity in an association of maize and palisade grass. Lower gravimetric humidity in 2020, compared to 2022, supported a period of precipitation lower than usual during summer. However, integrative systems may not require irrigation to maintain performance, which is significant to streamline farming activities, reduce expensive practices, and ultimately level up the cost-effectiveness of a project for stakeholders from crop to livestock producers [40]. Additionally, as the reference developed comparable properties to those in integrative systems and native vegetation, it supported the ability of the soil to recover itself over time.

5. Conclusions

We elaborated on integrative crop–livestock–forestry systems to mitigate anthropogenic degradation in tropical soil. We, therefore, established them by associating maize, palisade grass, and Eucalyptus in arrangements of single lines and triplicate rows. Then we monitored and assessed them for standard chemical and physical properties in the long term (nine years). Such interventions, especially a crop–livestock association, significantly recovered the Ultisol’s compositions and functions. Therefore, our study represents progress in developing and implementing eco-friendly solutions for environmental reclamation and sustainable production. Our practical models can offer stakeholders possibilities to overcome degrading conditions or processes while producing edible grains (i.e., corn and soybean), fodder (i.e., maize’s green foliage), and forage for human and animal consumption in harsher environments, such as marginal lands. Further larger-scale research must focus on conducting their techno-economic analysis and life-cycle assessment to complete characterization and commercial operation.