Strawberry Production with Different Mulches and Wetted Areas

Abstract

The use of mulch contributes to the reduction of water consumption and weed infestation in strawberry cultivation. Recycled paper, being biodegradable, has great potential to replace plastics. Thus, the objective was to evaluate the water consumption and agronomic performance of strawberry subjected to different wetted areas and mulches. The wet areas tested were 40% (WA40) and 70% (WA70) imposed by a drip irrigation system. The different types of mulch were: white polyethylene (WHP), black polyethylene (BLP), recycled paper (REP) and no mulch (NM). BLP, REP and WHP mulches promoted the same weed control. The number of fruits per plant, fruit length, fruit yield, and water productivity did not differ for the factors wetted area and types of mulch. Higher fruit mass and diameter were found in the WA40 treatment, while the mulches favored only fruit mass. Thus, fruit yield showed no difference, and only water consumption differed between the wet areas and between the types of mulch. Strawberry water consumption was higher in WA70. In relation to fruit waste, it was found that the WHP and BLP mulches provided higher values than REP and NM. Thus, the recycled paper, combined with a wet area of 40%, is recommended as a mulch in strawberry production.

1. Introduction

In Brazil, commercial production of strawberries (Fragaria × ananassa Duch.) is carried out in several states, with different cultivars, depending on adaptability to the climate. Among the states, Minas Gerais stands out as the leader in production, and the strawberries are distributed by several family farms. This makes strawberry cultivation an activity of economic and social relevance [1,2].

Agricultural production, in general, requires a large volume of water and, consequently, energy. According to Xue et al. [3], in order to save water, it is necessary to increase water use efficiency in agricultural production and avoid waste. Some alternatives to increase water use efficiency are the use of mulch [4], drip irrigation, and also irrigation with treated wastewater [5] or the application of organic compounds such as protein hydrolysates [6]. Mulch provides a reduction in water consumption by reducing evaporation and promotes lower leaching of nutrients by rainwater [7].

In addition to the water issue, the strawberry crop requires mulching to avoid direct contact of fruits with the soil and thus obtain greater control of diseases and pests. In this way, it is possible to harvest better quality fruits. In addition, mulching promotes control of invasive plants and increases fruit yield [7].

Polyethylene mulch has been the most used mulch in agricultural crops [8,9]. The major problem with this increasing use of polyethylene in agriculture is the generation of residues. Part of this inorganic material is abandoned in the agricultural area and often ends up being turned along with the soil or scattered in the field by the action of wind. In order to be recycled the plastic needs to be clean and the plastic that comes from mulching is impregnated with particles, so it requires washing [10]. Therefore, in many situations, the fate of the dirty material is that it ends up being burnt or disposed of in dumps, releasing toxic substances into the soil and atmosphere.

In addition to previously stated benefits that mulching provide, Yang et al. [11] report that it directly protects the soil against the action of wind and solar radiation, parameters that affect the water evaporation on the surface. Mulching influences the thermal regulation of the root zone and may interfere with the absorption of some nutrients [12]. Because of this, Orde et al. [13] report that the choice of color of the polyethylene for mulch will depend on local climatic conditions. The color white is the most recommended for warm regions, while the color black is the most appropriate for cold regions.

Jabran and Chauhan [14] suggest that biodegradable or renewable mulches should replace plastic mulches due to the environmental damage that the latter can cause. An alternative that seems feasible to replace polyethylene is the use of paper as mulch. Paper consists basically of cellulose, a natural and easily biodegradable polymer. However, Moreno et al. [15] report that aspects related to the degradation of paper mulches should be studied in more detail. Among the types of paper, recycled paper has shown great potential due to its durability and mechanical strength.

Haapala et al. [16] report that there are records dating back to 1934 on the use of paper mulch in agricultural production. Farmers used to use tar-saturated paper to prevent weed growth and reduce soil water evaporation in pineapple plantations in Hawaii. However, there is little scientific research on the use of this material as mulch, especially regarding the reduction of water evaporation. Despite this, some field data and model simulations indicate that biodegradable mulches promote soil moisture dynamics comparable to that obtained with polyethylene mulch [17,18].

In strawberry cultivation with mulch, the effective precipitation is reduced, so it is necessary to use irrigation for water replacement. Drip irrigation is the most widely used method for this production system [19]. In sprinkler irrigation systems, for example, 100% of the soil surface receives water, but in localized systems such as drip irrigation, only a fraction of the soil surface is wetted. Therefore, it is important to know the percentage of area wetted by the drippers [20,21]. Keller and Karmeli [22] recommend wetted areas of 20% for humid regions and 33% for semi-arid regions. However, Talens [23] indicates a minimum wetted area fraction of 50% for drip-irrigated vegetables, which may be increased according to the reduction of spacing and crop development stage. The wetted area impacts water consumption and root system development, enabling the roots to grow in the horizontal and vertical directions. Thus, research is necessary to find the wetted area that promotes lower water consumption and enables the plant to better explore the soil volume. Better soil exploration may result in greater absorption of nutrients, increasing yield and quality of strawberry fruits.

Tarjuelo et al. [24] agree that it is necessary to find a balance between water productivity and higher yields with marketable fruit quality. For Martinez-Ferri et al. [25], the improvement in water productivity involves plant physiology, the reduction of evaporation and drainage. As for evaporation, most of it can be blocked by mulch, while drainage can be contemplated with an adequate irrigation management program. It is common to observe excessive irrigation in strawberries because many producers work with intuitive management, based on previous experience, without making use of soil moisture measurement [26]. According to García-Tejero et al. [27], excessive irrigation of strawberries does not always result in good fruit production. On the other hand, water deficit can cause decreased absorption and transport of water by the roots, affecting fruit production, since strawberries are highly sensitive to water deficit [28]. Water deficit has been evaluated as a cause of interruptions in almost all physiological parameters [29]. Dehghanipoodeh et al. [30] observed a significant reduction in fresh and dry biomass of the strawberry root system under water deficit.

In view of the above, it is possible to notice the importance of determining the correct amount of water for irrigation. Different types of crop management certainly cause changes in strawberry water consumption. However, do these changes cause differences in the agronomic characteristics of this crop? In order to answer this question, the objective of this study was to evaluate the production of strawberries using different mulches and wet areas.

2. Materials and Methods

2.1. Characterization of the Area

The experiment was conducted in the experimental area of the Federal Institute of Southeastern Minas Gerais, Barbacena Campus, located in the municipality of Barbacena-MG, Brazil, in the Campo das Vertentes mesoregion, at 21° 13′ 42″ S latitude, 43° 46′ 04″ W longitude and with an average altitude of 1160 m. The soil of the region is classified as Cambissolo Háplico (Inceptisol), according to the classification of Embrapa [31]. The climate of the region is classified as Cwb, humid with dry winters and temperate summers, according to Alvares et al. [32].

Hourly data were collected for air temperature and relative humidity (Figure 1). These data were collected using an automatic meteorological station installed in the area.

To conduct the experiment, a protected environment with an area of 132 m² (5.3 m width and 25.0 m long) was built. The sides were protected with a polyethylene screen, while on the front and back parts, a 1-in-mesh screen was installed to allow greater airflow and access to pollinating insects. The arched structure was covered with 15-micron, low-density polyethylene (LDPE) film, protected against ultraviolet radiation. A removable shade net, which could be extended or retracted as needed, was installed under the ceiling, inside the protected environment. The shade net was removed when the outside temperature was above 30 °C.

Soil tillage was performed with a moldboard plow and then a rotating hoe to break up clods and raise the beds, approximately 30 cm high and 1.0 m wide. On these beds, 40 experimental units with a 1.65 m length and 1.65 m² area were demarcated. From these experimental units, soil samples were collected for physical-hydraulic and chemical characterization (

Table 1. Results of physical-hydraulic and chemical analyses of the soil before the experiment.

Layer	Ufc 1	Uwp 2	BD 3	Clay	Silt	Sand	TexturalClassification 4
(cm)	-------- (g g−1) --------		(g cm−3)	----------------- (%) ----------------
0–30	0.2499	0.1620	1.15	38.0	13.4	48.6	Sandy clay
pH	P	K	Ca	Mg	Al	H+Al	Zn	Fe
(H2O)	----- (mg dm−3) -----		------------------ (cmolc dm−3) ------------------				----- (mg dm−3) -----
6.7	242	187	4.1	0.8	0.0	1.4	13.2	43.8
Mn	Cu	B	S	SB 5	t 6	T 7	V 8	m 9
-------------------- (mg dm−3) --------------------				---------- (cmolc dm−3) ----------			--------- (%) ---------
47.3	7.4	1.0	1.4	5.4	5.4	6.8	79	0.0

¹ Moisture at field capacity by Richards’ pressure plate apparatus; ² Permanent wilting point; ³ Bulk density; ⁴ Classification of Embrapa [31]; ⁵ Sum of bases; ⁶ Effective cation-exchange capacity; ⁷ Cation-exchange capacity; ⁸ Base saturation; ⁹ Aluminum saturation. P, K, Fe, Mn, Cu and Zn extracted with Mehlich-1; Exchangeable Ca, Mg and Al extracted with 1 mol L⁻¹ KCl; Potential acidity at pH 7.0 extracted with 0.5 mol L⁻¹ calcium acetate.

).

The recommendation for strawberry fertilization varies according to the cultivation site, variety, and production system. Further, soil pH is fundamental for strawberry development since it interferes with the availability of nutrients to plants. For strawberry production, Pritts [33] recommends the pH range between 6.0 and 6.8. In this trial, acidity correction and chemical and organic fertilization of strawberries were performed based on the results of soil analysis and according to the recommendations of Nannetti and Souza [34]. Top-dressing fertilization was performed by fertigation through a drip system.

2.2. Plant Material and Cultural Practices

For planting, seedlings of the ‘San Andreas’ variety were acquired from a company registered with the Ministry of Agriculture. These seedlings were imported from Chile by suppliers who serve producers in the region of Barbacena-MG. The cultivar ‘San Andreas’ is day-neutral, was released in 2009 by the University of California, USA, and is recommended for fresh consumption. According to Gonçalves et al. [35], it is moderately resistant to powdery mildew (Podosphaera macularis), anthracnose (Colletotrichum fragariae and C. acutatum), verticillium wilt (Verticillium albo-atrum), and crown rot (Phytophthora cactorum), as well as being tolerant to the red spider mite (Tetranychus urticae).

The experimental period started on 22 June 2019, with the transplantation of 600 seedlings onto the beds with spacing of 0.33 × 0.33 m. Cultural practices and management of the plants followed the conventional crop routine. The plants were cleaned weekly to remove senescent leaves, stem, and stolons, when they appeared, favoring a better aeration among plants and also facilitating harvesting.

Cultivation in protected environments favors the growth of strawberry plants [36], as well as reducing the presence of insects, avoiding free water on the leaf from precipitation, and reducing the occurrence of diseases related to leaf wetting, which contributed to the reduction of phytosanitary treatments. On the other hand, it favored the appearance of red spider mite (Tetranychus urticae), which develops in a drier environment [37] and is noticed in leaves with silvery-white spots and controlled using biological acaricide, with Neoseiulus californicus as a predatory mite, thus avoiding the use of chemicals. With the use of adhesive yellow chromotropic traps it was possible to capture and identify Aphis forbesi, which were controlled with neem oil, whose main active ingredient is azadirachtin.

2.3. Characterization of the Experimental Assay

The experiment was conducted in a split-plot scheme, with the wetted areas in the plots and the different types of mulch in the subplots. The experimental design was randomized blocks, with five replicates. For the mulch factor, the treatments used were white polyethylene (WHP) and black polyethylene (BLP) films, recycled paper (REP), and a treatment with no mulch (NM). Polyethylene films were 22 μm thick and weighed 15 g m⁻², whereas the recycled paper (REP) was 187 μm thick and weighed 131 g m⁻² [18].

Wet areas were imposed by the irrigation system equipped with drip tapes, in order to provide wetted areas of 40 and 70%. Unlike sprinkler irrigation systems that wet 100% of the area, localized irrigation systems wet only a fraction of the area. Thus, the drip irrigation systems of the present study were chosen to provide wet area percentages of 40 and 70%.

For soil wet bulb measurement, tests were conducted with an irrigation time interval that contemplated the two wet areas, with the intervals being 5, 15, 25, and 35 min (infiltration time to determine the wet bulb dimensions). Measurements were performed 30 min after the emitter stopped operating, when a soil pit larger than the expected wet bulb was opened. With the use of a hoe and a digger, the dry region was cut into the wet bulb, according to the adaptation of the recommendations of Araújo et al. [20] and Battam et al. [38]. Measurements of surface dimensions (SDi), maximum dimensions (MDi), and maximum depths (MDe) were performed using a measuring tape with an accuracy of 1.0 mm (Figure 2).

The experimental unit consisted of three rows, containing five plants each (Figure 3). Only three plants of the central row were considered as usable areas to avoid interference from adjacent treatments, leaving a set of plants around them as borders.

2.4. Water Management

The water used for irrigation was taken from a point in the watercourse that was 1800 m away from the source. The water does not present any restrictions for its use in irrigation and its chemical characteristics are presented in

Table 2. Chemical characterization of irrigation water.

Parameter	Unit	Value
Bicarbonate	mg HCO3 L−1	14.6
Calcium	mg Ca L−1	5.08
Carbonate	mg CO3 L−1	<2
Iron	mg Fe L−1	<0.01
Magnesium	mg Mg L−1	1.61
Manganese	mg Mn L−1	<0.01
pH (In situ)	-	6.52
Sodium	mg Na L−1	0.08
Sulfate	mg SO4 L−1	13.0
Total Dissolved Solids	mg TDS L−1	25.7
Total Suspended Solids	mg TSS L−1	<5

.

At the beginning of the transplantation, sprinkler irrigations were performed to favor the establishment of seedlings, when mulch had not yet been placed on the soil. Before covering the soil, drip tapes with one emitter per plant, with a flow rate of 2 L h⁻¹, were installed. Then, the mulching material, which had already been previously perforated with 10 cm-diameter holes, guided by the spacing between the plants, was placed on the soil.

After this step, an irrigation depth was applied to raise the actual soil moisture to the content corresponding to field capacity. From this moment until the end of the cultivation cycle, only the amount of water required by the treatments was applied. This water requirement was determined based on the actual value of soil moisture.

Actual soil moisture was measured daily using the Hidrofarm sensor. For this, eight HFM 1020 soil moisture sensors with an HFM 2130 measuring device from the manufacturer Falker^® were used. According to the technical characteristics of this sensor, the manufacturer states accuracy of ±3%, resolution of 0.1%, a scale from 0 to 60%, measurement of layer thickness and diameter of 20 and 30 cm, respectively, and operation of a temperature range from 0 to 50 °C. The manufacturer also states that the technology used for measurement by the sensor is called high-frequency soil impedance—HFSI [39]. Although these sensors are purchased with factory calibration, Gava et al. [40] recommended calibration to avoid reading errors due to variations in the soil’s physical structure.

In order to avoid errors, the sensors were calibrated for the soil conditions of the experiment. To perform the calibration, the sensors were installed in pots of known volume and filled with soil from the beds. The soil was prepared, pounded to break up clods, sieved and homogenized; after the pots were filled, they were saturated from the bottom to the top. After drainage ceased in the eight pots (around 24 h), the sensors were installed in the center of each pot. After the procedures described above, the volumetric moisture began to be measured daily, at the same time, with the sensor. Then, the pots were weighed daily to obtain gravimetric moisture on a dry basis. These two measurements, sensor reading and weighing, were performed for 30 days. After the last reading, part of the soil from each pot was dried in an oven to determine moisture by the standard method [41]. The daily soil moisture by the gravimetric method was obtained and converted into volumetric moisture through bulk density determined for each pot. With the measured and estimated values, it was possible to perform the linear regression for each sensor to obtain the calibration equation for the readings to be performed in the experiment (Figure 4).

After calibration, the sensors were removed from the pots and transferred to the experimental units, enabling continuous monitoring of soil moisture. Two blocks were selected in the center of the protected environment to receive the sensors, contemplating the four levels of mulch and the two levels of wetting, as shown in Figure 3. The sensors were installed near the plants, on the opposite side of the pipe with the drippers. This care was taken to prevent water from coming into direct contact with the active area of the sensor blade and causing error in soil moisture reading.

According to the manufacturer, the value displayed by the Hidrofarm electronic meter refers to the average volumetric soil moisture present in a cylinder with 15 cm radius and 20 cm depth in the soil profile around the sensor.

To calculate the irrigation requirement in the different treatments, the readings with the Hidrofarm sensor were performed daily in the morning. After correction by the calibration curve, soil moisture data were used to determine the net irrigation depths (NID) through Equation (1).

$$NID = \mathit{1000} \left(Ufc - Ua\right) Z Pwa BD$$

(1)

where: NID—net irrigation depth; mm; Ufc—soil moisture corresponding to field capacity, g g⁻¹; Ua—actual soil moisture, g g⁻¹; Z—effective depth of the root system, m; Pwa—percentage of wetted area, decimal; and BD—bulk density, g cm⁻³.

The gross irrigation depth (GID) was obtained by means of NID and irrigation efficiency represented by the distribution uniformity coefficient (DU), Equation (2), according to Bernardo et al. [41]. DU showed a value of 93% and was determined immediately after the irrigation system was installed, following the recommendations of Keller and Karmeli [22].

$$GID =\frac{NID}{DU}$$

(2)

where: GID—gross irrigation depth, mm; NID—net irrigation depth; mm; and DU—distribution uniformity coefficient, decimal.

The irrigations were performed when the value of Ua approached the safety moisture value (Us), preventing Ua from decreasing to the point of becoming lower than Us. The Us value adopted was that corresponding to soil moisture content at which 40% of the water is available. Therefore, the dates of irrigations were different in each treatment.

The irrigation time for each treatment was calculated by Equation (3).

$$Ti =\frac{GID}{Ia}$$

(3)

where: Ti—irrigation time, h; GID—gross irrigation depth, mm; and Ia—application intensity; mm h⁻¹.

2.5. Evaluated Characteristics

To evaluate the weeds, it was decided upon to perform a manual control on the fourteenth day to standardize the experimental units, since there was still no mulch at the beginning. From this date, evaluations began to be performed in the weed community within the usable area of the treatments in a 0.25 m² area, using an inventory square of 0.50 × 0.50 m. Evaluations were performed at 28, 42, 56, and 70 days after strawberry transplantation. Weeds were collected, identified and then dried in the oven at a temperature of 60 °C for 72 h to obtain dry biomass using a precision scale. After the evaluation period of weeds, the mechanical control and monitoring of pests and diseases continued weekly in accordance with the Integrated Production Standards for strawberry crops [42].

Fruit harvests started approximately 87 days after seedling transplantation, and the fruits were harvested when they reached at least 75% of red coloration (Figure 5), when the fruits present 8.2° Brix of total soluble solids, as described by Costa et al. [43]. After harvest, the fruits were classified, counted, weighed on a precision scale and measured with a caliper. Fruits with diameters smaller than 15 mm, with rot and imperfections, were considered waste (non-marketable). Strawberry diameter is defined by the largest equatorial dimension of the fruit, an important aspect in their commercial classification, according to the Brazilian Program for the Modernization of Horticulture and Integrated Strawberry Production [42]. There are two main classes: class 15 comprising fruits with diameter from 15 to 35 mm, and class 35 comprising fruits with diameter greater than 35 mm.

In addition to the dry biomass of the weed community, the following agronomic and morphophysiological characteristics of strawberries were evaluated: average number of fruits per plant; average fruit mass (g); average fruit length (cm); average fruit diameter (cm); average marketable yield (kg m⁻²) and average fruit waste (fr pl⁻¹).

Water use productivity (WUP), obtained by the relationship between marketable yield and the volume of water used by the crop, expressed in kg m⁻³, was also evaluated using Equation (4).

$$WUP=\frac{Yield}{Vt}$$

(4)

where: WUP—water use productivity, kg m⁻³; Yield—marketable fruit yield, kg m⁻²; and Vt—the total volume of water applied, m³ m⁻².

2.6. Statistical Analysis

The data obtained in the strawberry cultivation were subjected to the analysis of variance F-test at 0.05 probability level. Regardless of whether or not the interactions between factors were significant, it was decided to decompose them. Then, the means were compared by Tukey test at 0.05 probability level. The statistical analyses were performed using the statistical program R [45].

3. Results and Discussion

3.1. Wet Area

The surface and maximum diameters of the wet bulb showed very similar values according to their curves presented in Figure 6. Based on the dimensions, the wet bulb showed a flattened shape, characteristic of clayey soil, thus showing a balance between gravitational force and soil hydraulic conductivity. Therefore, irrigation time played an important role in the wet bulb shape. When observing the maximum diameter, it is concluded that there was no formation of wet strip, because the test time was defined to exceed all irrigation times. The maximum depth reached by the roots in the present study was lower than the effective depth reported in the literature [46], so it is believed that the root system had to adapt to the wet bulb.

3.2. Water Consumption

To calculate the irrigation requirement (

Table 3. Accumulated values of net irrigation depth (mm) as a function of wet area and mulch.

--- CV (%) 1 ---		------------ F Test 2 ------------			WA(%)	Type of Mulch
WA 3	TM 4	WA	TM	WA×TM		WHP		BLP		REP		NM
0.27	0.39	<0.001	<0.001	<0.001	40	353	Ad	402	Ac	407	Ab	443	Aa
					70	479	Bd	484	Bc	498	Bb	522	Ba

¹ Coefficient of variation; ² Significance of mean squares; ³ Wet area; ⁴ Type of mulch (WHP—White polyethylene, BLP—Black polyethylene, REP—Recycled paper and NM—No mulch); Means followed by the same uppercase letter in the column (wetted areas) and lowercase letter in the row (mulch) do not differ from each other by Tukey test (p < 0.05).

), the daily actual moisture contents were determined with sensor use in each treatment, with safety moisture (Us) as the minimum moisture. The purpose was to provide conditions with no water restrictions for strawberries to develop optimally, aiming to obtain higher fruit yields. Due to the reduction in the wet area, there was an increase in irrigation frequency, promoting greater moisture in the soil surface layer. It is worth mentioning that to provide the treatments with different wetted areas, the WA40 treatment had to receive lower irrigation depths with higher irrigation frequency, while WA70 received higher irrigation depths with lower frequency.

Water consumption showed significant differences (p < 0.05) for all types of mulch and wetted areas, with very low coefficients of variation. The treatment with no mulch (NM) showed the highest water consumption, since the surface was exposed to evaporation. This occurred from the beginning of cultivation and during the cycle due to the cultural practices, when the strawberry plants undergo periodic pruning, exposing a smaller leaf area and causing greater exposure of the soil for evaporation. The other treatments were also subjected to the same conditions for transpiration, but they had polyethylene or recycled paper mulches that limit evaporation. While polyethylene is impermeable, REP allows the passage of a small amount of water through its wall, which is little permeable and hygroscopic [47]. This process occurred with water from evaporation under the mulch during the day or condensed at night. Thus, it was possible to notice the moist paper in the morning and, throughout the day, the external surface warmed with solar radiation, intensifying the loss of water to the atmosphere through evaporation. On the contrary, polyethylene returned water to the soil by gravitational action. Among polyethylene mulches, the white one led to the lowest consumption, which is certainly related to soil temperature [12].

At the end of the experiment, after opening the soil pits, it was possible to observe that the roots were concentrated in the volume of soil that received irrigation, that is, in the diameter equivalent to the wet area and in the first 20 cm of depth, a consequence of the irrigation adopted with 40 and 70% of wet area. According to Li et al. [48], the spatial distribution of the root system of a drip-irrigated crop is directly related to the dimensions of the wet bulb. In addition, Gendron et al. [49] report that strawberry roots are constantly renewed and their distribution in the soil depends on several factors such as soil compaction, moisture, aeration, temperature, and fertility.

3.3. Weeds

Figure 7 shows the number of weeds per species found in the different treatments and evaluation periods. In general, five weed species stood out, with Cyperus esculentuntus (48.61%) being the most frequent. Next, the most frequent species were: Galinsoga ciliata (12.37%), Oxalis latifolia (10.89%), Amaranthus viridis (7.89%), and Parthenium hysterophorus (5.69%). The other weed species that were identified were: Brachiaria decumbens (3.52%), Verbascum virgatum (2.83%), Brassica rapa (2.69%), Euphorbia heterophylla (1.31%), Conium maculatum (0.97%), Nothoscordum gracile (0.83%), Ipomoea purpurea (0.80%), Sonchus oleraceus (0.51%), Leonurus sibiricus (0.49%), Commelina benghalensis (0.23%), Solanum americanum (0.20%), and Ricinus communis (0.17%).

Table 4. Weed shoot dry biomass (g m⁻²) at four different times and as a function of wet area and mulch.

-- CV 1 (%) --		---------- F Test 2 ----------			DAT 5	WA (%)	Types of Mulch
WA 3	TM 4	WA	TM	WAxTM			WHP		BLP		REP		NM
41.5	39.4	0.231	>0.001	0.320	28	40	6.54	Ab	7.76	Ab	6.70	Ab	15.30	Aa
						70	9.00	Ab	8.36	Ab	9.23	Ab	37.55	Aa
					42	40	9.23	Ab	9.57	Ab	5.58	Ab	17.05	Aa
						70	7.21	Ab	10.02	Ab	7.98	Ab	21.16	Aa
					56	40	6.68	Ab	9.85	Ab	7.85	Ab	12.01	Aa
						70	8.97	Ab	10.15	Ab	6.62	Ab	13.27	Aa
					70	40	8.45	Ab	9.00	Ab	6.93	Ab	12.22	Aa
						70	9.00	Ab	8.11	Ab	7.77	Ab	13.57	Aa

¹ Coefficient of variation; ² Significance of mean squares; ³ Wet area (40 and 70%); ⁴ Type of mulch (WHP—White polyethylene, BLP—Black polyethylene, REP—Recycled paper and NM—No mulch); ⁵ Days after transplanting. Means followed by the same uppercase letter in the column (wetted areas) and lowercase letter in the row (mulch) do not differ from each other by Tukey test (p < 0.05).

shows that the different wetted areas did not affect the shoot dry biomass production by the weeds. However, higher values were expected for the 70% of wet area, since, in this treatment, there was a larger wetted area for weeds to develop, but this significant difference did not occur. Possibly, no differences were verified because of the high values of coefficient of variation. According to Willden et al. [37], cultivation in a protected environment favors the faster and more vigorous growth of weeds, increasing their variation in response to uncontrolled conditions.

The different mulches reduced the shoot dry biomass of the weeds, corroborating the results found by Silva et al. [18]. On average, black polyethylene (BLP), white polyethylene (WHP) and recycled paper (REP) reduced the dry biomass of weeds by 44.5% in WA40 and 60.1% in WA70, when compared to the NM treatment. At 28 and 42 days after transplantation (DAT), higher values of dry biomass were found in the NM treatment, which decreased from 56 DAT. This occurred due to the increase in strawberry leaf area, shading and contributing to the suppression of weeds.

It is worth noting that REP did not differ from any plastic mulch, regardless of the wet area or evaluation time. This shows that REP has low transmittance to light, to the point that weeds are not stimulated to grow. Another positive aspect of this material was that, despite being biodegradable, its decomposition occurred over a period longer than the strawberry cultivation cycle, suppressing weeds throughout this period.

3.4. Agronomic Characteristics

Table 5. Agronomic characteristics of strawberries as a function of wetted areas and types of mulch.

Factor	-- CV 1 (%) --		---------- F Test 2 ----------			WA (%)	Types of Mulch
	WA 3	TM 4	WA	TM	WAxTM		WHP		BLP		REP		NM
NF 5	45.0	28.4	0.228	0.442	0.788	40	45.13	Aa	48.20	Aa	41.53	Aa	41.04	Aa
(fr pl−1)						70	50.07	Aa	61.20	Aa	47.67	Aa	57.07	Aa
FM 6	9.2	4.8	0.054	0.257	0.036	40	14.74	Aab	13.75	Ab	14.95	Aa	14.43	Aab
(g fr−1)						70	13.05	Ba	13.42	Aa	13.15	Ba	13.90	Aa
FL 7	18.2	12.1	0.662	0.352	0.545	40	3.91	Aa	3.86	Aa	3.92	Aa	3.86	Aa
(cm)						70	4.23	Aa	3.72	Aa	4.26	Aa	3.77	Aa
FED 8	2.1	2.9	0.006	0.905	0.329	40	2.95	Aa	2.91	Aa	2.97	Aa	2.94	Aa
(cm)						70	2.81	Ba	2.87	Ba	2.81	Ba	2.87	Ba
Y 9	42.8	28.6	0.344	0.550	0.493	40	6.05	Aa	5.93	Aa	5.54	Aa	5.29	Aa
(kg m−2)						70	5.96	Aa	7.55	Aa	5.69	Aa	7.18	Aa
WUP 10	45.9	28.5	0.618	0.279	0.387	40	17.16	Aa	14.78	Aa	13.78	Aa	11.95	Aa
(kg m−3)						70	12.44	Aa	15.61	Aa	11.42	Aa	13.76	Aa
Wst 11	48.1	35.7	0.177	<0.001	0.935	40	0.40	Ab	0.35	Ab	0.79	Aa	0.65	Aa
(fr pl−1)						70	0.48	Ab	0.52	Ab	0.99	Aa	0.77	Aa

¹ Coefficient of variation; ² Significance of mean squares; ³ Wet area (40 and 70%); ⁴ Type of mulch (WHP—White polyethylene, BLP—Black polyethylene, REP—Recycled paper and NM—No mulch); ⁵ Number of fruits per plant; ⁶ Fresh mass; ⁷ Fruit length; ⁸ Fruit equatorial diameter; ⁹ Fruit yield; ¹⁰ Water use productivity; ¹¹ Waste. Means followed by the same uppercase letter in the column (wetted areas) and lowercase letter in the row (mulch) do not differ from each other by Tukey test (p < 0.05).

presents a summary of the analysis of variance for the parameters analyzed according to the factors studied. It was observed that the wetted areas and types of mulch did not cause single or interaction effects on the variables number of fruits, fruit length, fruit yield and water productivity in strawberries. The interaction between the analyzed factors had an effect only on the fresh mass of strawberries. There were also single effects of the wet area on fruit diameter and of types of mulch on strawberry fruit waste.

The number of fruits per plant is an important characteristic in strawberry production and has a great impact on the economic viability of this agricultural activity. The number of fruits per plant (Table 5) showed no difference for wetted areas or types of mulch. Research studies reveal that the mulches used in agricultural crops for promoting changes in soil temperature interfere in the development and production of plants [50,51]. In the present study, possibly, the mulches did not cause differences in temperatures capable of generating effect on this strawberry characteristic.

Results showed that the wetted areas did not affect the fresh mass per fruit in the treatments in which the soil was mulched with black polyethylene and with no mulch. In the other treatments (WHP and REP), there were higher values of fresh mass per fruit under the 40% of wet area. Possibly, this characteristic is more sensitive to soil water content. The WA40 treatment has a smaller wetted area and, consequently, a smaller volume of stored water. Thus, the WA40 treatment received water more frequently and the soil remained longer with moisture content close to field capacity. Thus, strawberry plants experienced lower soil moisture for a longer period of time in the WA70 treatment.

The types of mulch did not affect the fresh mass per fruit of strawberry plants when they received irrigation with a wetted area of 70%. In the 40% of wet area, there was a higher fresh mass per fruit when the soil was mulched with recycled paper compared to the treatment with black polyethylene. Lewers et al. [52], working with the cultivar ‘San Andreas’, obtained similar results. This shows that recycled paper has the potential to be used as mulch in strawberry production.

Wetted areas and types of mulch did not influence the length of strawberry fruits. However, fruit diameter showed differences between wetted areas, with higher values for WA40, whereas the types of mulch caused no difference in this characteristic. According to the values of average fruit diameter, the production was classified as class 15. Despite the difference in wetted areas, fruit diameter was relatively homogeneous, as can be noticed by the small differences between the means and the low values of coefficient of variation. Biometric characteristics such as fruit length, diameter, and fresh mass are important for strawberry production, especially when fruits are intended for fresh consumption [53].

Fruit yield was not affected by the wetted areas and types of mulch. At first, one may have a false impression that the mulches were not useful to favor strawberry plants and to obtain a greater profit in this agricultural activity. However, the correct thing to think is that, with lower water and energy expenses, it is possible to produce the same amount of strawberries when using mulch. It should also be considered that the NM treatment, in practice, has higher expenses with weed control operations. On the other hand, if this control is not performed, lower strawberry yield is expected in the system with no mulch. There was also a better performance of the 40% of wet area, since it promoted lower water consumption and did not differ from the other treatment in terms of strawberry fruit yield. Thus, the 40% of wet area is sufficient for strawberry irrigation by the drip irrigation system.

Despite differences in water consumption between treatments, water use productivity was not affected by the factors studied. Possibly, this happened due to the fruit yield having presented a high value of coefficient of variation. This parameter is the numerator of the equation for calculating the water use productivity. Thus, the Water use productivity also presented a high value of coefficient of variation and differences between treatments were not detected by analysis of variance. The average value of water productivity, considering all treatments, was 13.9 kg m⁻³. This result indicates that a volume of 72 L of irrigation water was necessary to produce 1 kg of fresh mass of strawberries, corroborating the results reported by other studies under similar conditions [26,54,55,56].

Fruit waste was not affected by the wetted areas, and lower values were found in treatments with polyethylene mulch. Possibly, in the REP and NM treatments, some fruits came into contact with the wet surface, resulting in contaminations that caused greater rot [3]. The plant material used in the present study is more susceptible to rot problems. Flanagan et al. [57] found higher fruit losses caused by rot in the cultivar ‘San Andreas’, compared to other strawberry cultivars. It is worth noting that recycled paper allows a slight moistening through its wall [47]. On the other hand, polyethylene mulches are impermeable and did not allow this contact of the fruit with the irrigation water applied on the soil surface.

In view of this study, it was possible to observe that the reduction in the wet area contributed to the water consumption and agronomic performance of strawberries. With regard to recycled paper as mulch, the results are similar to those obtained with polyethylene, which pollutes the environment due to its slow decomposition, and this is its biggest negative aspect [8]. However, we must also be careful when choosing the recycled paper to be used, because depending on the content of pigments, metals, etc., we can also cause problems for the crop and the environment. Thus, it is important to continue studying recycled paper as a viable alternative for mulching. Therefore, further studies need to be conducted to evaluate the waterproofing and pigmentation of recycled paper as mulch. In that way, the results will directly benefit strawberry growers and the environment.

4. Conclusions

The search for water sustainability and agronomic performance of strawberries involves a reduction in water consumption and an increase in yield.

Mulching reduces water consumption and suppresses weeds. In relation to recycled paper, the results are positive when thinking of a solution with biodegradable mulch for the soil, that is, it was equivalent to polyethylene in weed control, the number of fruits, fruit yield and water productivity. However, the variables fruit waste and water consumption showed disadvantages compared to polyethylene, which can be corrected with waterproofing and pigmentation of recycled paper.

Reducing the wet area in irrigation management using a drip system causes a reduction in water consumption, but in general does not alter weed infestation and the agronomic characteristics of strawberries.

Considering the advantages and disadvantages in strawberry production, the use of recycled paper as mulch and 40% of wet area are recommended.