Protease Supplementation in the Diet of Finishing Pigs: Implications on the Quality of Organic Fertilizers for Forage Production and Soil Chemical Composition

Abstract

The study evaluated the inclusion of protease in the diet of pigs in the final phase, analyzing its effects on residues used as organic fertilizer (OF) for corn silage cultivation. Conducted at the Federal Institute of Education, Science and Technology of Goiano, Rio Verde Campus, the experiment had three phases: the use of protease in intensive pig production, production of OF—pig slurry (PS), and its application in corn silage cultivation. The inclusion of protease in the diet did not affect the final weight of the pigs, with a mean of 89.75 kg. The use of PS from this production system did not affect the forage mass (23.64 Mg ha⁻¹). On the other hand, in the short term, PS without enzyme both at sowing and covering, biofertilizer with enzyme at sowing and urea at covering, and PS with enzyme both at sowing and covering increased magnesium levels in the soil, with values ranging from 1.40 to 1.44 cmol_c dm⁻³. Although protease did not affect animal performance in the finishing phase, the waste produced by this production system influenced the soil’s chemical composition; furthermore, the use of PS from systems with or without enzymes could partially replace chemical fertilization.

1. Introduction

The inclusion of proteases in the diets resulted in greater efficiency in the utilization of feed intake food, according to the study by Ndazigaruye et al. [1]. The use of proteases has been particularly beneficial for young broiler chickens, regardless of the levels of crude protein in the diet, demonstrating its positive effects mainly in terms of body weight and feed conversion. Despite this strategy enhancing the utilization of feed intake, primarily by reducing nitrogen excretion, which can mitigate the polluting effect of this waste [2], there is still a need to propose appropriate ways to dispose of the waste produced in intensive production systems.

Ferreira et al. [3] found that the use of pig liquid manure–pig slurry (PS) can be used for hay production in Cynodon spp. pastures. By using this waste as organic fertilizer, it promoted increases in forage mass production. However, in the pig production chain, the formulation of diets for animal nutrition does not follow a single pattern. Each phase of the production chain requires a ration suitable for its specific nutritional requirements. This diversity in ratio composition enables different types of waste, with distinct proportions of macro and micronutrients.

Therefore, conducting experimental trials to assess the effects of different diets on the quality of organic fertilizers (OF) used in agricultural production systems is essential. Understanding the effects of different ration formulations in pig production is crucial to ensure that the produced OF are suitable and effective as substitutes for chemical fertilizers.

We hypothesized that the inclusion of protease in the animals’ diet may boost their performance but it will reduce the nitrogen waste level in this system. Consequently, when used as OF in corn (Zea mays) production, it may not fully meet the nutritional demands to achieve maximum forage production. On the other hand, it is expected that the use of these wastes as fertilizer will contribute to the improvement in soil chemical composition.

The objective of this study was to evaluate the inclusion of protease in the diet for the pig finishing phase and its impacts on the waste produced, which is intended to be used as OF in different ferti-irrigation strategies for corn cultivation, maximizing its potential for forage production

2. Materials and Methods

2.1. Location and Experimental Procedures

The experiment was conducted in the experimental area belonging to the Federal Institute of Education, Science, and Technology of Goiano, Rio Verde Campus, located in Rio Verde, Brazil (17°47′53″ S, 50°55′41″ W, 748 m). The experimental period occurred from September to the year 2017 and concluded in March 2018.

The climate of the region is Aw tropical with two defined seasons, a rainy summer, and a dry winter, with an annual precipitation of 1414 mm and an average annual temperature of 23.1 °C [4]. During the experimental period, precipitation, maximum, minimum, and average temperatures were recorded (Figure 1).

The experiment was separated into three stages: the first stage focused on the use of proteases in pig production in an intensive production system; the second stage was dedicated to the production of PS from the production systems; and the third stage involved the use of the PS in corn silage production (Figure 2).

2.2. Experimental Design—Pig Performance

Twelve castrated male pigs of high genetic potential for carcass meat deposition, which were crossbred (Landrace × Large White) and aged 115 days (finishing phase) were randomly assigned to 1 of 2 treatments. The animals were distributed in a completely randomized block with two treatments: without protease (n = 6), where animals consumed a basal diet with no protease, or with protease (n = 6), where the animals consumed a basal diet with 0.05% of protease. Each animal was considered an experimental unit.

The duration of the animal production phase was 35 days. To determine performance parameters, all animals were individually weighed at the beginning and at the end of the experimental period.

2.3. Animal Housing and Handling

The animals were housed in pens equipped with manual feeders and nipple drinkers, located in a masonry shed with a concrete floor and covered with fiber cement tiles. The diets (Table 1) were formulated based on ground corn and soybean meal, vitamins, and minerals to meet the nutritional needs of the animals according to their phase, following the recommendations outlined by Rostagno et al. [5]. Animals were fed once a day ad libitum and refusal was logged from each animal to determine intake and feed efficiency.

During the animal performance phase, the following characteristics were determined: initial weight (kg), final weight (kg), daily weight gain (g day⁻¹), daily feed intake (g day⁻¹), and feed efficiency (kg of dry matter intake·kg of live weight gain⁻¹).

2.4. Pig Slurry (PS) Production

Five days after the start of the experimental period of the animal performance phase, animal waste was collected daily. The collected samples were stored in 500 L polyethylene tanks separated according to the treatment the animals received in this stage of the trial (without protease and with protease). After sample collection, the tanks were sealed for a minimum of 60 days to allow for anaerobic fermentation of the waste and production of the PS.

Samples of the produced organic fertilizers, pig slurry without protease (PS) and pig slurry with protease (PSP), were properly packaged and sent to a specialized commercial laboratory (Rio Verde, Brazil) for chemical analysis to determine the levels of total solids, organic matter, moisture, acidity (pH), and macro and micronutrients (Table 2). These results were subsequently used for fertilizer calculations for forage production.

2.5. Experimental Design—Forage Production

The area used for forage production measured 629 m² and was subdivided into 35 experimental plots measuring 3 m in length by 3 m in width, totaling 9 m² each. Within these plots, 1 m² at the center was considered as the usable area for data collection, excluding the borders. The recommended spacing between plots was 1 m. The corn production phase began in March 2018 and ended in July 2018.

The soil in the experimental area was classified as Red Latosol (Oxisol) [6]. Prior to the experiment’s implementation, soil samples were taken from the 0–20 cm depth layer for analysis of the physical and chemical soil characteristics (Table 3). The area underwent vegetation desiccation before the experiment began and soil plowing and harrowing were performed.

The forage seeding was mechanically performed (at 3 centimeters depth) using a commercial and conventional early maize hybrid, 22S18, with a density of 70,000 seeds ha⁻¹, as recommended for the southwestern region of the state of Goiás, Brazil. The seeds were treated with the insecticide Cropstar^® (Imidacloprid and Thiodicarb) at a dosage of 0.300 L 60,000 seeds⁻¹.

The seven treatments constituting this experimental stage were a combination of fertilization at seeding and topdressing, as shown in Table 4. Chemical fertilization (CF) at seeding and urea (U) topdressing; CF at seeding and PS without enzyme topdressing; PS without enzyme at seeding and urea topdressing; biofertilizer without enzyme both at seeding and topdressing; chemical fertilization at seeding and PSP topdressing; biofertilizer with enzyme at seeding and urea topdressing; and PSP both at seeding and topdressing.

At seeding, nitrogen chemical sources, phosphorus, and potassium were used for fertilization, while the second fertilization (topdressing), according to the applied treatment, was performed when the plants were between the phenological development stages of BBCH16 to BBCH18 (six and eight expanded leaves, respectively) [7]. Both fertilizations were manually applied with the aid of watering cans for distribution in the experimental plots.

Throughout the crop development, all plots received equal treatments for the ant, fall armyworm (Spodoptera frugiperda), fungus, and Dalbulus maidis (corn leafhopper) control.

2.6. Characteristics Evaluated in Forage Production

The moment of maize harvest was determined based on the percentage of dry matter in the plant, recommended between 30% and 35%. Before harvesting the forage, data were collected regarding the morphological characteristics of the plants: (i) plant height, measured from the soil surface to the insertion point of the flag leaf; (ii) height of the first ear insertion; (iii) ear diameter, measured at the center of the ear before shelling, using a caliper; (iv) ear length, defined as the distance between the first and last grain of the longest row; and (v) stem diameter, which is the circumference of the first internode above the plant base. These variables were collected from all plants in the experimental plots.

All whole plants from the experimental plots were weighed to determine the forage mass (Mg ha⁻¹). The plants were chopped into 2.0 cm particles using a stationary forage chopper, then homogenized and sub-sampled in a volume of 500 g to be placed in brown paper bags, and dried in a forced air oven at 55 °C for approximately 72 hours or until reaching constant weight.

2.7. Soil Analysis

After the conclusion of the maize production experiment, soil samples were collected from each experimental unit at a depth of 0–20 cm. The following chemical parameters were determined: organic matter (g dm⁻³), active acidity (pH in CaCl₂), potential acidity (cmol_c dm⁻³), cation exchange capacity (cmol_c dm⁻³), base saturation (V%), calcium (cmol_c dm⁻³), magnesium (cmol_c dm⁻³), phosphorus (mg dm⁻³), potassium (mg dm⁻³), sulfur (mg dm⁻³), iron (mg dm⁻³), manganese (mg dm⁻³), zinc (mg dm⁻³), copper (mg dm⁻³), and boron (mg dm⁻³) [8].

2.8. Statistical Analysis

In the animal performance experimental phase, the collected data were subjected to analysis of variance, with a significance level of 5% using the F-test. The analyses were conducted using the R computational program [9] (Vienna, Austria). Information related to the initial weight of the animals was not subjected to statistical analysis; only mean values were presented descriptively.

The data from maize production and soil chemical composition were subjected to analysis of variance and means were compared using the Tukey test at a significance level of 5%, using the R computational program [9].

3. Results

3.1. Pig Performance

At the beginning of the experimental period, animals from both experimental groups had an average weight of 53.64 kg. Despite the inclusion of protease in the diet, animals in the finishing phase demonstrated proportional growth, reaching an average final weight of 89.75 kg (Table 5).

No significant effects of protease supplementation were identified by other animal production parameters. The recorded mean values were 1049 g day⁻¹ for daily weight gain, 3.09 g day⁻¹ for daily feed intake, and 2.94 for feed conversion ratio (Table 5).

3.2. Effect of OF on Morphological Characteristics and Forage Mass

Fertilization effect was observed for plant height and height of the first ear insertion (Table 6). Thus, for these two characteristics, the highest values were recorded when chemical fertilization was used at seeding and urea at topdressing.

For the other characteristics related to maize morphology and forage, no fertilization effect is recorded (Table 6). Therefore, for stem diameter, ear length, ear diameter, and forage mass and average values of 27.48 mm, 23.97 cm, 56.63 mm, and 23.64 Mg ha⁻¹, respectively, are measured.

3.3. Effect of Biofertilizer on Soil Chemical Composition

Fertilization strategies influenced the concentrations of magnesium and sulfur (Table 7). Therefore, the highest values of magnesium were obtained in treatments with biofertilizer with and without enzyme at both seeding and topdressing and with urea at topdressing. Meanwhile, for sulfur levels, the highest results were obtained when chemical fertilization was performed at seeding and biofertilizer without enzyme at topdressing.

Fertilization strategies did not exhibit effects on the other soil chemical parameters (Table 7). Therefore, average values were measured as follows: 37.34 g dm⁻³ for organic matter, 5.45 for active acidity, 4.11 cmol_c dm⁻³ for potential acidity, 8.75 cmol_c dm⁻³ for cation exchange capacity, 54.69% for base saturation, 3.37 cmol_c dm⁻³ for calcium, 2.86 mg dm⁻³ for phosphorus, 122.51 mg dm⁻³ for potassium, 24.54 mg dm⁻³ for iron, 32.14 mg dm⁻³ for manganese, 1.87 mg dm⁻³ for zinc, 3.30 mg dm⁻³ for copper, and 0.193 mg dm⁻³ for boron.

4. Discussion

4.1. Animal Performance

The role of protease in animal feeding is to enhance the absorption of proteins and amino acids present in the diet, resulting in a significant increase in animal performance within the production system [10]. Optimizing the productivity of livestock not only reduces soil contamination but also contributes to the sustainability of agriculture, aiming to produce high-quality food to meet the needs of the human population [2].

However, the analyzed characteristics such as final weight, average daily weight gain, and feed conversion in the finishing phase of high-genetic-potential pigs were not affected by the inclusion of protease in the diet. These results are consistent with the findings of Stephenson et al. [11], who did not observe significant differences in the performance parameters of finishing pigs when fed diets formulated to meet the nutritional requirements of the animals, regardless of the presence or absence of protease.

This outcome may be associated with the physiological factors of these animals, considering that, in the finishing phase, the demand for protein for muscle mass development is reduced, as highlighted by Nones et al. [12]. This suggests a decrease in the effects on characteristics related to animal production in this specific phase.

4.2. Forage Production and Soil Chemical Composition

In the study conducted using OF from scenarios with different diets, it was found that the fertilization strategy using chemical fertilizer at seeding and urea at topdressing promoted the highest values of plant height and height of the first ear insertion. Urea is a chemical fertilizer source that ensures the immediate supply of nitrogen to the plant. When provided adequately, it accelerates tissue flow, increasing the rate of expansion and elongation of each plant’s vegetative tissue [13,14].

On the other hand, regarding the other morphological characteristics of the plants, the lack of differences between fertilization strategies is linked to phenotypic plasticity. Regardless of the fertilization management applied to the plant, the growth of the components of each plant, such as stem diameter, ear length, and ear diameter, proved to be proportional. Additionally, there was also proportionality in forage production. Based on these results, it can be inferred that, although management with chemical fertilization at seeding and urea at topdressing resulted in larger plants, the produced tillers exhibited the same specific weight as those from other strategies used, highlighting the notable adaptive capacity of the forage to different management scenarios.

Based on the results indicating similar forage mass among the management strategies, it is plausible to infer that pig slurry, both with and without protease, can serve as a partial substitute for chemical fertilization. The use of organic sources from the industrialized agricultural chain has considerable potential to be employed in forage and grain production, as evidenced by Silva et al. [15], Teodoro et al. [16], and Rodrigues et al. [17]. These studies highlighted that in the production of sunflower achenes (Helianthus annuus), forage mass of Mombaça guinea grass (Megathyrsus maximus cv. Mombaça), and Marandu palisade grass (Urochloa brizantha cv. Marandu), the use of OF from intensive animal production systems (such as chicken litter and liquid blood) or the sugar–alcohol industry (such as filter cake) can partially replace chemical fertilizers.

Regarding the soil chemical composition in the 0–20 cm layer, chemical components such as organic matter, active acidity, potential acidity, cation exchange capacity, base saturation, calcium, phosphorus, potassium, manganese, zinc, copper, and boron were not affected by the fertilization strategies. In tropical climate regions, it is not possible to generate significant changes in soil chemical composition in the short term with the use of OF. Thus, to promote significant changes in the soil, especially in organic matter and phosphorus content, it is crucial to apply organic fertilizer continuously in the long term [18,19,20].

On the other hand, it was observed that the tested treatments affected magnesium and sulfur levels. The three fertilization strategies—PS both at seeding and topdressing; PSP at seeding; urea at topdressing; and PSP both at seeding and topdressing—indicate that the increase in magnesium concentration is not related to issues with the use of protease, since fertilization with PS also resulted in high values of this nutrient. In the case of sulfur concentration, the highest values were obtained with management using chemical fertilization at seeding and biofertilizer PS at topdressing.

The addition of both magnesium and sulfur did not result in a proportional increase in soil negative charges as there was no increase in active acidity that would typically cause this effect. Consequently, the lack of charges to retain the addition of these two cations led them, largely, to remain dissolved in the soil solution, making them highly susceptible to leaching [21,22].

Given the complexity of the interactions between different types of Fert-irrigation and their influences on soil characteristics and plant development, the potential of organic sources from the agricultural industry to partially supplement chemical Fert-irrigation becomes evident. While varied Fert-irrigation strategies do not seem to significantly impact soil chemical composition, the study highlights the importance of continuous use of OF to promote more substantial changes, especially in organic matter and phosphorus levels.

5. Conclusions

The use of protease does not influence the performance of pigs in the finishing phase. However, the residue generated by this production system can be employed in forage production, resulting in a proportional increase in forage mass, allowing for the partial replacement of inorganic fertilizer sources. Furthermore, in the short term, the use of pig slurry (with or without protease) only affects soil sulfur and magnesium contents.

Author Contributions

Conceptualization, A.C.M., F.R.d.A.N. and A.P.C.G.; methodology A.P.C.G., R.E.C., A.C.M., R.C.M. and K.C.G.; software, F.R.d.A.N. and P.B.F.; validation, A.C.M., A.P.C.G., P.B.F. and F.d.F.C.; formal analysis, F.R.d.A.N. and P.B.F.; investigation, K.C.G.; resources, F.R.d.A.N.; data curation, F.R.d.A.N. and P.B.F.; writing—original draft preparation, A.C.M., R.E.C. and P.B.F.; writing—review and editing, R.E.C. and F.d.F.C.; visualization, A.P.C.G.; supervision, A.P.C.G. and F.d.F.C.; project administration, A.C.M.; funding acquisition, A.P.C.G. and F.d.F.C. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

All experimental protocols were approved by the IF GoianoEthical Committee in the Use of Animals (decision 7413151117).

Data Availability Statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Acknowledgments

We would like to express our sincere gratitude to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior–Brasil (CAPES) for the financial support provided for this study. We also extend our appreciation to the University of Maryland and Goiano Federal Institute of Education, Science, and Technology (IF Goiano) for the support provided. Their contribution was instrumental to the success of this work.

Conflicts of Interest

The authors have no conflicts of interest to declare that are relevant to the content of this article.

Footnotes

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Figures and Tables

Figure 1. Precipitation and temperature (maximum, minimum, and average) during the experimental period.

Figure 2. Conceptual model of pig slurry (PS) production and utilization in forage plant Fert-irrigation.

Table 1

Ingredients and chemical composition of finishing pig diet fed during the experimental period (115–150 days).

	Protease
Item	Without	With
Ingredient 1
Corn (%)	72.45	72.45
Soybean meal (45%)	18.61	18.61
Soybean oil (%)	2.50	2.50
Soybean hulls (%)	2.62	2.62
Inert fat (%)	1.30	1.30
Dicalcium phosphate (%)	0.850	0.850
Limestone (%)	0.800	0.800
Sodium chloride (%)	0.300	0.300
L-Lysine HCl (%)	0.100	0.100
Vitamin supplement 1 (%)	0.250	0.250
Mineral supplement 2 (%)	0.200	0.200
DL-Methionine (%)	0.001	0.001
Butylated hydroxytoluene (BHT) (%)	0.015	0.015
Protease * (%)	-	0.05
Total	100.00	100.00
Calculated nutritional composition 3
Metabolizable energy (Kcal kg−1)	3260	3260
Crude protein (%)	15.16	15.16
Digestible lysine (%)	0.679	0.679
Digestible Methionine + Cystine (%)	0.455	0.455
Digestible threonine (%)	0.470	0.470
Digestible tryptophan (%)	0.143	0.143
Calcium (%)	0.599	0.599
Available phosphorus (%)	0.251	0.251
Sodium (%)	0.153	0.153

¹ Containing at least per kilogram: 2,000,000 IU of vitamin A; 250 mg of vitamin B1; 1000 mg of vitamin B2; 500 mg of vitamin B6; 5000 mcg of vitamin B12; 12.5 g of vitamin C; 300,000 IU of vitamin D3; 5000 IU of vitamin E; 625 mg of vitamin K3; 2500 mg of pantothenic acid; 150 mg of folic acid; 12.5 mg of biotin; 500 mg of butylated hydroxytoluene; 60 g of choline and 6260 mg of niacin. ² 125 mg of cobalt; 5000 mg of copper; 17.5 g of iron; 200 mg of iodine; 10 g of manganese; and 125 mg of selenium; 20 g of zinc and vehicle q.s.p. 1000 g; ³ Nutritional composition calculated based on the Rostagno et al. [5]; * Commercial protease produced from Bacillus licheniformis (Curitiba, Brazil).

Table 2

Chemical composition of the biofertilizers.

	Protease
Item	Without	With
Acidity (pH)	5.33	5.66
Organic matter (g dm−3)	5.6	5.8
Density (g dm−3)	1027	1033
Nitrogen (g dm−3)	9.2	8.8
Phosphorus (g dm−3)	1.6	2.0
Potassium (g dm−3)	0.8	0.8
Calcium (g dm−3)	3.0	3.8
Magnesium (g dm−3)	0.8	1.0
Sulfate ion (mg dm−3)	0.6	0.8
Iron (mg dm−3)	258.0	387.8
Manganese (mg dm−3)	40.0	50.4
Copper (mg dm−3)	93.0	115.4
Zinc (mg dm−3)	49.2	54.0

Table 3

Chemical and physical composition of the soil in the 0–20 cm layer.

Item	Quantity
Active acidity (pH in CaCl2)	5.62
Organic matter (g dm−3)	57.6
Base saturation (V%)	43.0
Cation exchange capacity (cmolc dm−3)	8.2
Calcium (cmolc dm−3)	2.2
Magnesium (cmolc dm−3)	0.5
Aluminum (cmolc dm−3)	0.00
Potential acidity (cmolc dm−3)	4.6
Potassium (mg dm−3)	320
Sulfur (mg dm−3)	5.8
* Phosphorus (mg dm−3)	2.8
Sodium (mg dm−3)	4.0
Iron (mg dm−3)	14.6
Manganese (mg dm−3)	41.8
Copper (mg dm−3)	3.2
Zinc (mg dm−3)	16.1
Boron (mg dm−3)	0.5
Clay (%)	46
Silt (%)	5
Sand (%)	49

* Melich 1.

Table 4

Experimental treatments applied in corn cultivation.

	Fertilization
Treatments	Seeding	Topdressing
CF/U	Chemical fertilizer (40 kg N ha−1, 100 kg P ha−1, and 90 kg K ha−1)	Urea (130 kg N ha−1)
CF/PS	Chemical fertilizer (40 kg N ha−1, 100 kg P ha−1, and 90 kg K ha−1)	PS (15 m3 ha−1) and Urea (130 kg N ha−1)
PS/U	Biofertilizer without enzyme (14 m3 ha−1) correctedfor P (85 kg P ha−1) and K (77 kg K ha−1) with SS and KCl fertilizers	Urea (130 kg N ha−1)
PS/PS	Biofertilizerwithout enzyme (14 m3 ha−1) correctedfor P (85 kg P ha−1) and K (77 kg K ha−1) with SS and KCl fertilizers	PS (15 m3 ha−1) and Urea (130 kg N ha−1)
CF/PSP	Chemical fertilizer (40 kg N ha−1, 100 kg P ha−1, and 90 kg K ha−1)	PSP (15 m3 ha−1) and Urea (130 kg N ha−1)
PSP/U	Biofertilizer with enzyme (14 m3 ha−1) correctedfor P (85 kg P ha−1) and K (77 kg K ha−1) with SS and KCl fertilizers	Urea (130 kg N ha−1)
PSP/PSP	Biofertilizer with enzyme (14 m3 ha−1) corrected for P (85 kg P ha−1) and K (77 kg K ha−1) with SS and KCl fertilizers	PSP with enzyme (15 m3 ha−1) and (130 kg N ha−1)

CF/U: Treatment receiving chemical fertilization at seeding and urea at topdressing; CF/PS: Treatment receiving chemical fertilization at seeding and pig slurry without enzyme at topdressing; PS/U: Treatment receiving pig slurry without enzyme at seeding and urea at topdressing; PS/PS: Treatment receiving pig slurry without enzyme both at seeding and topdressing; CF/PSP: Treatment receiving chemical fertilization at seeding and pig slurry with enzyme at topdressing; PSP/U: Treatment receiving pig slurry with enzyme at seeding and urea at topdressing; PSP/PSP: Treatment receiving biofertilizer with enzyme both at seeding and topdressing. N: Nitrogen. P: Phosphorus. K: Potassium. SS: Single superphosphate. KCl: Potassium chloride.

Table 5

Performance of finishing pigs (115–150 days) when fed diets with or without protease.

Characteristics	Without	With	p-Value	SEM
Initial weight (kg)	53.22	54.05	-	-
Final weight (kg)	91.50	88.00	0.311	0.292
Daily weight gain (g day−1)	1094	1004	0.164	7.50
Daily feed intake (g day−1)	3.15	3.02	0.567	0.011
Feed conversion (kg of dry matter intake × Kg of live weight gain−1)	2.88	3.00	0.203	0.010

p-value: Probability of significant effect. SEM: Standard error of the mean.

Table 6

Morphological characteristics and forage mass of corn plants as a function of different fertilization strategies.

Item	CF/U	CF/PS	PS/U	PS/PS	CF/PSP	PSP/U	PSP/PSP	p-Value	SEM
Plant height (cm)	222.79 a	211.48 b	206.46 b	216.80 a	216.51 a	218.30 b	205.45 b	0.036	1.69
Stem diameter (mm)	27.46 a	23.45 a	23.31 a	25.74 a	25.14 a	23.70 a	22.45 a	0.054	0.472
Height of the first ear insertion (cm)	120.88 a	103.25 ab	99.31 b	110.34 ab	112.74 ab	111.33 ab	101.80 b	0.012	1.83
Ear length (cm)	27.15 a	27.34 a	27.75 a	28.75 a	27.57 a	26.63 a	27.17 a	0.266	0.222
Ear diameter (mm)	57.14 a	56.30 a	55.93 a	57.88 a	57.11 a	55.24 a	56.83 a	0.475	0.339
Forage mass (Mg ha−1)	28.30 a	23.36 a	25.08 a	22.85 a	18.80 a	25.94 a	21.13 a	0.151	0.589

Means followed by the same lowercase letters within rows do not differ significantly at the 5% level of probability. CF/U: Treatment receiving chemical fertilization at seeding and urea at topdressing; CF/PS: Treatment receiving chemical fertilization at seeding and pig slurry without enzyme at topdressing; PS/U: Treatment receiving pig slurry without enzyme at seeding and urea at topdressing; PS/PS: Treatment receiving pig slurry without enzyme both at seeding and topdressing; CF/PSP: Treatment receiving chemical fertilization at seeding and pig slurry with enzyme at topdressing; PSP/U: Treatment receiving pig slurry with enzyme at seeding and urea at topdressing; PSP/PSP: Treatment receiving biofertilizer with enzyme both at seeding and topdressing. p-value: Probability of significant effect. SEM: Standard error of the mean.

Table 7

Soil chemical composition at the 0–20 cm layer as a function of different fertilization strategies.

Item	CF/U	CF/PS	PS/U	PS/PS	CF/PSP	PSP/U	PSP/PSP	p-Value	SEM
Organic matter (g dm−3)	37.30 a	37.00 a	35.84 a	37.26 a	37.30 a	39.40 a	37.30 a	0.902	0.629
Active acidity (pH in CaCl2)	5.33 a	5.33 a	5.38 a	5.64 a	5.43 a	5.61 a	5.43 a	0.243	0.041
Potential acidity (cmolc dm−3)	3.88 a	4.68 a	4.20 a	4.08 a	4.06 a	3.62 a	4.24 a	0.351	0.116
Cation exchange capacity (cmolc dm−3)	9.10 a	7.36 a	8.96 a	9.14 a	8.56 a	8.94 a	9.16 a	0.765	0.314
Base saturation (%)	57.20 a	50.40 a	55.20 a	55.20 a	52.00 a	59.40 a	53.40 a	0.568	1.26
Calcium (cmolc dm−3)	3.86 a	3.44 a	3.10 a	3.42 a	3.02 a	3.60 a	3.18 a	0.824	0.156
Magnesium (cmolc dm−3)	1.00 b	1.02 b	1.44 a	1.40 a	1.16 ab	1.40 a	1.40 a	0.045	0.052
Phosphoru (mg dm−3)	3.02 a	5.50 a	2.04 a	2.10 a	2.18 a	2.98 a	2.18 a	0.200	0.393
Potassium (mg dm−3)	137.20 a	143.20 a	107.8 a	98.20 a	129.40 a	127.20 a	114.60 a	0.391	5.92
Sulfur (mg dm−3)	7.8 ab	13.84 a	9.14 ab	3.88 b	9.38 ab	5.88 b	4.14 b	0.001	0.769
Iron (mg dm−3)	21.44 a	23.58 a	25.26 a	24.68 a	25.10 a	28.98 a	22.72 a	0.956	1.69
Manganese (mg dm−3)	35.88 a	30.44 a	32.44 a	38.16 a	30.54 a	33.72 a	23.78 a	0.539	1.86
Zinc (mg dm−3)	2.38 a	2.24 a	1.78 a	1.34 a	1.86 a	1.76 a	1.76 a	0.679	0.154
Copper (mg dm−3)	3.44 a	3.20 a	3.50 a	3.38 a	3.16 a	3.20 a	3.22 a	0.936	0.089
Boron (mg dm−3)	0.160 a	0.200 a	0.100 a	0.220 a	0.180 a	0.220 a	0.270 a	0.220	0.014

Means followed by the same lowercase letters within rows do not differ significantly at the 5% level of probability. CF/U: Treatment receiving chemical fertilization at seeding and urea at topdressing; CF/PS: Treatment receiving chemical fertilization at seeding and pig slurry without enzyme at topdressing; PS/U: Treatment receiving pig slurry without enzyme at seeding and urea at topdressing; PS/PS: Treatment receiving pig slurry without enzyme both at seeding and topdressing; CF/PSP: Treatment receiving chemical fertilization at seeding and pig slurry with enzyme at topdressing; PSP/U: Treatment receiving pig slurry with enzyme at seeding and urea at topdressing; PSP/PSP: Treatment receiving biofertilizer with enzyme both at seeding and topdressing. p-value: Probability of significant effect. SEM: Standard error of the mean.

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