Biodegradable Recycled Paper Mulch Reduces Strawberry Water Consumption and Crop Coefficient

Abstract

Mulching with recycled paper has the potential to be used in agricultural production and can be adopted in strawberry cultivation. Therefore, the objective of this study was to evaluate the agronomic characteristics, water consumption and technical coefficients of strawberry cultivated with recycled paper as mulch. The treatments consisted of strawberry cultivation in lysimeters with recycled paper mulch and without soil cover. The recycled paper used was 187 μm-thick. The irrigation system was installed with drippers whose flow rate was 2 L h⁻¹. Strawberry irrigation requirements were 317 and 394 mm, with and without mulch, respectively. Mulching with recycled paper did not have a significant effect on the average number of fruits, fresh fruit mass, fruit waste per plant, average fruit yield and water productivity. In relation to the technical coefficients, maximum values of the evaporation coefficient (Ke) of 0.40 (calculated with the evapotranspiration of the grass—L) and 0.28 (calculated with the Penman–Monteith ETo—PM) were obtained for OPM. The Kc values for the initial and full development stages were 0.31 and 0.84 (L) and 0.24 and 0.66 (PM), respectively. NDVI can be used to estimate strawberry Kc values. Recycled paper as mulch reduces the water consumption of strawberry crops and does not alter the agronomic characteristics.

1. Introduction

Strawberry is a crop of social and economic importance, as it requires a lot of manpower in its cultivation and provides income in a short period [1]. In Brazil, the commercial production of strawberry (Fragaria × ananassa Duch.) is mostly carried out on family farms.

According to Antunes et al. [2], about 5200 ha of strawberry is annually cultivated in Brazil, showing a production of about 218,881 tons with an average yield of approximately 42 t ha⁻¹. This yield is lower than the average of the largest strawberry producers, the United States and Spain, which achieve yields above 50 t ha⁻¹. This value suggests that Brazil has the potential to grow in strawberry production without having to open new areas.

An important technique to increase the quality and yield of strawberry is irrigation. The supply of water via irrigation is necessary because strawberry is mostly cultivated in protected environments. In the open, the use of irrigation is justified due to the irregularity of rainfall, which can be exceeded by crop evapotranspiration. Currently, this has been intensified by global climate change, where we have seen a greater number of extreme events [3]. Thus, adequate supply of water via irrigation has been the guarantee to produce as planned, preventing the lack of rainfall from altering the previously established quality, yield and profitability [4].

Irrigated agriculture requires a large volume of water [5]. Therefore, many studies are conducted aiming at water saving to increase efficiency in agricultural yield and avoid waste [6]. Several methods can be pursued to save irrigation water and/or face conditions of water scarcity, such as use of wastewaters [7], protein hydrolysates [8] and even with the support of sensors [9]. Alternatives to reduce water consumption include the use of mulch. Yang et al. [10] state that mulch directly protects the soil surface against the action of wind and radiation, the main factors responsible for soil water evaporation, with a consequent reduced irrigation volume [9]. With this technique, water consumption is reduced due to the decrease in soil water evaporation. At the same time, mulching modifies the value of surface albedo and promotes a transfer of sensitive heat and irradiance from the mulch surface to the plant canopy. This phenomenon changes crop transpiration [11].

In addition to maintaining soil moisture and reducing water consumption by agricultural crops, mulching has the function of controlling invasive plants, even affecting the weed composition [10,12]. For strawberry crops, mulching also has the function of ensuring the quality of fruits, preventing them from having direct contact with the soil and reducing problems with diseases and pests.

According to Yang et al. [10] and Santin et al. [13], plastic film as mulch has become the preference in agriculture due to the reduction in water consumption and easy management. Kaur and Kaur [14] also report that mulching with polyethylene has become a common practice due to the advantages it provides for the soil, such as increased temperature, reduced leaching of nutrients, preservation of the physical structure and easy handling. An increase in soil temperature benefits the strawberry root system, stimulating the development of radicles. These small roots are responsible for the absorption of water and nutrients and contribute to an earlier production [15]. Király et al. [16] also observed higher growth of strawberry roots with mulch as compared to the cultivation without mulch.

The negative aspect with the increasing use of polyethylene in agriculture is the generation of waste, which causes environmental pollution due to negligence [10]. After the crop cycle, it is not possible to reuse the plastic as a mulch for a new cultivation cycle [17]. Part of this inorganic material is abandoned in the agricultural area and mixed with the soil. In other situations, they are piled up in the fields awaiting removal for recycling, which does not always occur. The plastic of mulch, after use, intended for recycling, needs to go through the washing process, which requires high water consumption [18]. The contaminated material ends up being burned in the field, which releases toxic substances, polluting the soil and the atmosphere, or is disposed in dumps. According to Solis and Silveira [19], it is necessary to reduce the amount of discarded plastic in circulation in the environment.

Jabran and Chauhan [20] 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 is the substitution of polyethylene by paper as mulch. Paper consists basically of cellulose, a natural and easily biodegradable polymer. Recycled paper has proven to have great potential due to its durability and mechanical strength. Field data and model simulations indicate that paper and biodegradable plastic mulches promote soil moisture dynamics comparable to that obtained with polyethylene mulch [21]. Moreno et al. [22] state that biodegradable plastic and paper mulches are being used, but aspects related to their degradation should be studied in more detail. However, there is little scientific research on the use of this material as mulch, especially regarding water saving and information for irrigation management.

One of the ways to evaluate water consumption by plants is by determining the crop coefficient (Kc). For Doorenbos and Pruitt [23], these values need to be calibrated for specific climatic conditions. Lozano et al. [24] recommend that Kc values and the durations of development stages should be adjusted for each region according to the crop, climatic conditions and cultivation techniques used.

According to García-Tarejo et al. [25], the excess water applied to strawberry does not translate into higher yield. Therefore, it is important to know local information, such as Kc, climate data and soil characteristics, which will make it possible to determine the actual need for irrigation at each stage of the crop, resulting in water savings without causing damage to production and to the environment. Gavilán et al. [26] state that the best way to estimate water consumption is by using crop evapotranspiration (ETc). ETc is the product between the quantification of atmospheric demand given by reference evapotranspiration (ETo) and the surface characteristics given by Kc [11,27].

A current option for estimating the crop coefficient (Kc) is the application of vegetation indices [28,29]. As the variation in Kc values is directly related to the phenological cycle of crops, some studies suggest that the temporal profiles of vegetation indices can be used [30,31,32]. The normalized difference vegetation index (NDVI), which indicates plant growth and development [33,34], is a promising tool for irrigation management [35,36]. Dingre et al. [37] report that several researchers, working with different crops, have found correlations ranging from 0.80 to 0.95 when studying the relationship between NDVI and Kc.

In view of the above, the objective of this study was to evaluate the agronomic characteristics, water consumption and technical coefficients for the irrigation management of strawberry cultivated with recycled paper as mulch.

2. Materials and Methods

2.1. Experimental Area

The experiment was conducted at the Teaching, Research and Extension Unit (UEPE) of Irrigation and Drainage of the Agricultural Engineering Department (DEA) of the Federal University of Viçosa (UFV), Viçosa Campus, located in the municipality of Viçosa, MG—Brazil, at 20°46′09″ S latitude, 42°51′45″ W longitude and with altitude of 674 m. The climate of the region is classified as Cwa, humid temperate, with a dry winter and a hot summer, according to Alvares et al. [38].

The experiment was conducted using 16 drainage lysimeters belonging to the Irrigation and Drainage sector of DEA-UFV. These lysimeters are boxes with a surface area of 1.68 m², depth of 0.65 m and a 0.05 m-high edge above the ground to avoid water inflow and outflow by surface runoff. The lysimeters were filled with clayey soil classified as Latossolo Vermelho-Amarelo distrófico (Oxisol), according to Embrapa [39]. However, Perea et al. [40] state that strawberry develops better in soils with good drainage and good organic matter content. Based on this information, the soil of the lysimeters was removed, pounded to break up clods and sand was added to improve drainage. The lower part of the lysimeter received a 0.05 m-thick layer of crushed stone No. 0, covering the drainage pipe, followed by a 0.20 m-thick intermediate layer of sand and ending with a 0.35 m-thick layer of the Oxisol mixed with sand. Samples of this new soil were collected and the physical-hydraulic and chemical parameters were determined, as shown in

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

Layer			Ufc 1			Uwp 2			BD 3			Clay				Silt			Sand				Textural Classification 4
(cm)			(g g−1)						(g cm−3)			(%)
0–35			0.208			0.160			1.11			24.7				4.3			71.0				Sandy clay loam
35–55			0.015			0.008			1.43			1.3				0.7			98.0				Sand
Layer	pH			P			K			Ca			Mg		Al			H+Al			SB 5			t 6		T 7
(cm)	(H2O)			(mg dm−3)						(cmolc dm−3)
0–35	5.66			2.5			23			0.64			0.18		0.0			1.4			0.88			0.88		2.28
35–55	6.62			2.9			3			0.17			0.06		0.0			0.2			0.24			0.24		0.44
Layer		V 8			m 9			OM 10			Prem 11			S			B			Cu		Mn			Fe		Zn
(cm)		(%)						(dag kg−1)			(mg L−1)			(mg dm−3)
0–35		38.6			0.0			0.67			24.4			31.0			0.10			2.13		36.2			129.9		1.72
35–55		54.5			0.0			-			51.0			-			-			-		-			-		-

¹ Moisture at field capacity by Richards’ pressure plate apparatus. ² Permanent wilting point. ³ Bulk density. ⁴ Classification of Embrapa [39]. ⁵ Sum of bases. ⁶ Effective cation-exchange capacity. ⁷ Cation-exchange capacity. ⁸ Base saturation. ⁹ Aluminum saturation. ¹⁰ Organic matter. ¹¹ Remaining phosphorus. 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. pH in water, KCl, and CaCl₂—1:2.5 ratio.

.

Acidity correction and chemical and organic fertilization of strawberry were performed based on the results of soil analysis and according to the recommendations of Nannetti and Souza [41]. Limestone (calcitic, RNV = 90%) was added to the soil of the lysimeters at a dose equivalent to 2.2 t ha⁻¹ to correct the pH. Then, 60 t ha⁻¹ of well-aged corral manure was also added to increase the organic matter content, incorporated in the 0–20 cm layer. According to Pritts [42], the pH interferes with the availability of nutrients, activity of microorganisms and diseases in crops.

For fertilization, N was applied at a dose of 220 kg ha⁻¹, with ammonium sulfate as the source (20% N), split into 7.7 g per week for each experimental unit (lysimeter). Phosphorus (P) was applied at a dose of 400 kg ha⁻¹, with P₂O₅ as the source, at planting, along with part of N and K, mixed in the upper 10 cm of the soil. The potassium dose (K₂O) was 350 kg ha⁻¹, with 70% applied at planting and the remainder split and distributed weekly. Boric acid was applied at a dose of 1.5 g per liter of water during the flowering stage.

According to Lee et al. [43], strawberry cultivation inside a protected environment can help mitigate adverse weather conditions, keeping plants within a comfort zone. For Lozano et al. [24], the protected environment is the main mechanism to prevent diseases in strawberry, besides the use of healthy seedlings, which drastically reduces the use of agrochemicals and favors environmental balance. Additionally, according to Lozano et al. [24], strawberries are grown in polyethylene tunnels in most of the world. Thus, to assist in the management, a protected environment was built above the lysimeters with an area of 89.3 m² (8.5 m-wide by 10.5 m-long). The sides were protected with a 2 m-high polyethylene screen, leaving open spaces for ventilation. The structure had two spans on the opposite sides with removable curtains to allow airflow for natural ventilation and access of pollinating insects. The protected environment cover received a 150-micron, low-density polyethylene (LDPE) film, protected against ultraviolet radiation.

2.2. Experimental Design

The experiment was setup following a randomized block design with four replicates. Four treatments were applied: strawberry cultivation without the use of recycled paper mulch (SWoP), strawberry cultivation with the use of recycled paper mulch (SWiP), lysimeter receiving only recycled paper mulch (OPM) and lysimeter cultivated with Bahiagrass (CBG). The recycled paper used was 187 μm-thick and weighed 131 g m⁻² [32] and 0.10 m-diameter circular openings were made for transplantation according to the spacing of the seedlings.

2.3. Lysimeter Management

The experiment began on 5 June 2019, when seedlings of the San Andreas variety were transplanted. These seedlings were imported from Chile by suppliers that serve strawberry producers in the region of Barbacena, MG. It should be noted that the company is registered with the Ministry of Agriculture, Livestock and Food Supply (MAPA) of the Brazilian government.

Strawberry (Fragaria × ananassa Duch.) was cultivated with spacing of 0.33 × 0.33 m and each lysimeter was planted with three rows containing five plants each. Of these 15 plants per lysimeter, 3 plants of the central row were used for evaluations, leaving a set of plants around them as borders. Before starting the experiment, the lysimeters were saturated to raise the soil moisture content to field capacity.

For the strawberry crop cultivated with mulch, a drip irrigation system was installed, because it is the most often indicated [44]. Subsequently, the recycled paper mulch was placed on the soil, after being perforated with 10 cm-diameter openings according to the crop spacing (Figure 1).

Irrigation was performed daily throughout the crop cycle. The net irrigation depth applied was determined using Equation (1):

$$\mathrm{NID}=\frac{\mathrm{V}}{\mathrm{A}}$$

(1)

where: NID—net irrigation depth, mm; V—volume of water applied, L; A—lysimeter area, m².

Before each irrigation, drainage was measured to calculate the daily evapotranspiration of the crop. Drainage water was collected in containers, inside a shelter, with the aid of a drainage network installed at the bottom of each lysimeter and then the volume was measured using a graduated cylinder. It is worth mentioning that all the percolate collected daily in each experimental unit was reapplied together with the irrigation water in that same lysimeter to ensure the balance of salts and nutrients in the soil.

2.4. Evapotranspiration and Technical Coefficients

A Davis Vantage Pro II automatic weather station was used in the experiment to collect hourly data of solar radiation, relative humidity, wind speed and air temperature. With these data, it was possible to estimate the reference evapotranspiration (ETo) and then compare it with the values measured in lysimeters cultivated with Bahiagrass.

ETo was determined through the standard FAO-56 Penman–Monteith method [11], using Equation (2). Daily ETo was determined by integrating the hourly ETo values from 9 a.m. on one day to 8 a.m. on the following day.

$$\mathrm{ETo}=\frac{0.408\Delta \left({\mathrm{R}}_{\mathrm{n}}-\mathrm{G}\right)+\mathsf{\gamma }\frac{37}{{\mathrm{T}}_{\mathrm{a}}+273}{\mathrm{U}}_2\left({\mathrm{e}}_{\mathrm{s}}-{\mathrm{e}}_{\mathrm{a}}\right)}{\Delta +\mathsf{\gamma }\left(1+0.34{\mathrm{U}}_2\right)}$$

(2)

where: ETo—reference evapotranspiration, mm h⁻¹; R_n—net radiation on the surface, MJ m⁻² h⁻¹; G—soil heat flux density, MJ m⁻² h⁻¹; T_a—average air temperature, °C; U₂—wind speed at 2 m height, m s⁻¹; e_s—saturation vapor pressure, kPa; e_a—partial vapor pressure, kPa; Δ—slope of the saturation vapor pressure curve, kPa °C⁻¹; γ—psychrometric coefficient, kPa °C⁻¹.

Crop evapotranspiration (ETc) was determined from the water balance, which is based on the mass conservation law, as shown in Equation (3):

$$\mathrm{Pr}+\mathrm{NID}-\mathrm{D}-\mathrm{ETc}=\pm \Delta \mathrm{h}$$

(3)

where: Pr—precipitation, mm; NID—net irrigation depth, mm; D—deep drainage depth, mm; ETc—crop evapotranspiration, mm; Δh—variation in soil water storage, mm.

To avoid large variations in soil water storage and keep the soil with a moisture content close to the field capacity, irrigations were carried out daily. Thus, this term of the mass conservation equation became small and was then disregarded in the water balance. In addition, rainfall was also nullified by the protected environment. For water drainage to occur in the lysimeters, excess irrigations were performed (10% higher than the ETc of the previous day). According to these considerations, Equation (3) was simplified, resulting in Equation (4):

$$\mathrm{ETc}=\mathrm{NID}-\mathrm{D}$$

(4)

where: ETc—crop evapotranspiration, mm; NID—net irrigation depth, mm; D—deep drainage depth, mm.

In lysimeters cultivated with Bahiagrass, the ETc obtained through Equation (4) was assumed to be ETo.

The strawberry crop coefficient (Kc) was calculated daily using Equation (5):

$$\mathrm{Kc}=\frac{\mathrm{ETc}}{\mathrm{ETo}}$$

(5)

where: Kc—crop coefficient, dimensionless.

The soil water evaporation coefficient (Ke) was determined daily with the data from the treatment that had only recycled paper mulch (OPM), using an adaptation of Equations (6) and (7), proposed by Allen et al. [11]:

$$\mathrm{ETc}=\mathrm{ETo}\mathrm{Kc}$$

(6)

$$\mathrm{Kc}=\left(\mathrm{Kcb}\mathrm{Ks}\right)+\mathrm{Ke}$$

(7)

where: Kcb—basal crop coefficient, dimensionless; Ke—soil water evaporation coefficient, dimensionless; Ks—stress coefficient, dimensionless.

Due to the daily irrigations, that is, high frequency (one-day irrigation interval), the Ks value was assumed to be equal to the unit. Therefore, in the first term of Equation (7), only the basal crop coefficient (Kcb) remained. Thus, Kcb was obtained from the difference between Kc values from treatments with strawberry cultivation with and without mulch and Ke was obtained from the treatment with only recycled paper.

The strawberry cycle was divided into phenological stages based on the growth period in accumulated degree-days or vegetative period, related to soil shading by the leaf area. The accumulated degree-days of strawberry were determined following the method of Arnold [45], using a lower basal temperature of 7 °C [46,47]. Below this temperature, strawberry plants go into dormancy.

Cultural practices and management of the plants followed the conventional crop routine. The plants were cleaned weekly to remove senescent leaves, stems and stolons, when they appeared, favoring a better aeration among plants and facilitating harvesting. The cultivation in the protected environment, in addition to reducing the presence of insects, avoided rainwater from falling on the leaves, reducing the occurrence of diseases related to leaf wetting, which contributed to the reduction of phytosanitary treatments. Weeds were controlled by means of manual weeding, performed every day.

2.5. Evaluated Characteristics

Fruit harvests started approximately 79 days after transplanting the seedlings and the fruits were harvested when they reached at least 75% of red color, as described by Costa [48]. During harvest, the three central plants of each experimental unit were separated for evaluation. The harvested fruits were classified as marketable or non-marketable. Fruits with rot and imperfections were considered waste and were non-marketable. After classification, the fruits of each plant were counted and weighed on a precision scale and the following parameters were evaluated: average number of fruits per plant, fresh fruit mass per plant, average marketable yield per area (kg m⁻²) and fruit waste per plant. In addition, water productivity, obtained by the ratio between marketable yield and the volume of water consumed by strawberry plants, expressed in kg m⁻³, was obtained using Equation (8) [44]:

$$\mathrm{WP}=\frac{\mathrm{Yield}}{\mathrm{Vt}}$$

(8)

where: WP—water use productivity, kg m⁻³; yield—marketable yield of strawberry fruits, kg m⁻²; Vt—total volume of water applied, m³ m⁻².

During the strawberry cycle, a Trimble GreenSeeker portable agricultural sensor was used to obtain the normalized difference vegetation index (NDVI). This reading was performed on alternate days and accompanied the phenological development of the plant, which can be used as an alternative in Kc monitoring, according to Oliveira et al. [36].

The NDVI given by the sensor is obtained by emitting red and infrared light and then measuring the amount of each type of light that is reflected to the target. The sensor displays the measured value in terms of an NDVI reading (ranging from 0.00 to 0.99). In practice, the value expresses the presence and intensity of vegetation at the site [49].

Before the end of the experiment, the root system biomass was measured. To this end, the shoots of strawberry plants were removed and a 200 mm-diameter probe with beveled edges, centered on the strawberry crown, was introduced up to a 50 cm depth. Then, a hoe and a clam-shell digger were used to remove the soil around the cylinder to facilitate its removal from the site. The removal of soil with roots in the cylinder was carried out in layers every 10 cm. Separation and cleaning of roots were performed by adapting the Gottingen method [50], through successive washes of the material over a sieve. Next, each portion of the fresh mass sample was placed in a paper bag, weighed on a precision scale and dried in an oven at 60 °C for 72 h. Finally, the material was weighed to determine the dry mass of roots.

2.6. Data Analysis

To determine the technical coefficients, the Kc values (average of five days) were plotted as a function of the accumulated thermal sum (accumulated degree-days—ADD), to fit the models that can be used by technicians and farmers. The length of the model intervals and the union point (node) of two consecutive intervals were determined by means of the multivariate adaptive regression splines (MARS) technique, initially proposed by Friedman [51]. The models used were polynomial, fitted by means of the coefficient of determination (R²) and minimization of the error, estimated by the root mean square error (RMSE), as shown in Equation (9):

$$\mathrm{RMSE}=\sqrt{\frac{{\displaystyle \sum }{\left(\mathrm{Pd}-\mathrm{O}\right)}^2}{\mathrm{n}}}$$

(9)

where: RMSE—root mean square error; Pd—predicted value of Kc; O—observed value of Kc; n—sample size.

Regarding the agronomic and morphophysiological characteristics of strawberry, the data were subjected to the analysis of variance F-test. Normality and homoscedasticity of the residuals were evaluated considering the Shapiro–Wilk and Bartlett tests, respectively. Then, the means were compared by Tukey’s test at the 0.05 probability level. Statistical analyses were performed using the statistical program R [52].

3. Results and Discussion

3.1. Evaporation Coefficient (Ke)

Data were collected in the experiment to obtain the technical and agronomic coefficients of strawberry in lysimeters prepared and cultivated with strawberry without recycled paper mulch (SWoP), strawberry using recycled paper mulch (SWiP), with only recycled paper mulch (OPM) and cultivated with Bahiagrass (CBG). With these data, soil evaporation coefficients (Ke) were obtained using two methodologies. In the first, Ke consisted of the relationship between the evaporation measured in the lysimeter and the evapotranspiration of the grass obtained by the lysimeter (L) method. In the second methodology, evaporation was divided by reference evapotranspiration (ETo), obtained by the Penman–Monteith (PM) method fed with data from the automatic weather station (Figure 2). Thus, it is possible to provide technical coefficients considering two strategies for strawberry water management. It is also possible to observe the behavior of the technical coefficients using two methodologies for estimating the ETo.

Most of the soil water evaporation in the treatment that had only recycled paper mulch without plants (OPM) occurred through the free opening coinciding with the wet bulb of the dripper and, to a lesser extent, through the paper, which is permeable and hygroscopic [30]. In the L approach, the Ke was 0.40 at 1019 ADD, followed by a slight decrease until reaching the value of 0.39 at 2019 ADD. In the PM approach, Ke was constant throughout the cultivation cycle and assumed the value of 0.28. When comparing the L and PM methods, a higher Ke was verified with the former, because of the high frequency of excess irrigations, performed to generate drainage. This also contributed to the error (RMSE) of the L approach being greater compared to that of PM.

It is worth noting that the small drop in Ke values in the L approach and the constant Ke values in the PM approach occurred due to the presence of recycled paper as mulch. In conventional strawberry cultivation, a reduction in Ke values would be expected as a function of the increase in the leaf area index, as reported by Allen et al. [11]. Santos and Tiwari [53], evaluating the banana crop without mulching, found that the Ke values decreased as the leaf area index increased. This happened due to the increase in the area shaded by the crop, reducing the incidence of direct solar radiation on the soil.

3.2. Basal Crop Coefficient (Kcb)

In the phase of establishment and acclimatization of strawberry seedlings, transpiration was low and showed great oscillation, so it was not possible to make correct estimates of the basal crop coefficient (Kcb). According to García-Tarejo et al. [25], appropriate estimates should be made from 30 to 40 days after transplanting (DAT). Thus, it was possible to start recording Kcb at 286 ADD, 30 DAT. Figure 3 shows that three Kcb intervals could be obtained in the lysimeter method and two intervals could be obtained in the PM method. For both methods, the first change of the slope of the line occurred at 888 ADD, when the stage of the crop cycle changed. In the L method, the Kcb value at 286 ADD was 0.08, increasing linearly from this point until 888 ADD, reaching a value of 0.68. This value was constant until 1482 ADD and then it increased up to 0.84 at 2019 ADD. In the PM approach, the Kcb value at 286 ADD was 0.05 and then it increased linearly until reaching 0.48 at 888 ADD and 0.72 at 2019 ADD.

It is also verified, according to Figure 3, that the L approach showed a better fit of the regression equation, with higher coefficients of determination and a lower error according to the RMSE value. It is worth noting that in the L approach, the ETo was measured and in the PM approach the ETo was estimated through the meteorological elements, justifying this behavior. However, the L approach is rarely used in water management, due to its high cost and the need for qualified personnel to handle the lysimeters. Thus, the L approach is more often used in research for better performance and the PM approach by farmers due to the lower cost and ease of use [54,55].

The first interval began with the emergence of the new leaves in the formation of the plant canopy, resulting in a rapid increase of Kcb. In the second interval, with full growth and production, Kcb stabilized until 1482 ADD, when it continued with a less vigorous increase, approaching Kc, as a consequence of the decrease in soil water evaporation due to the mulch. It is important to highlight that weekly cleaning and thinning of senescent leaves, stolons and stems are necessary in strawberry management. These procedures enable the emergence of new leaves and flowers and the new leaves of strawberry are abundant in stomata, which allow intense transpiration [56].

3.3. Single Crop Coefficient (Kc)

According to Allen et al. [11], Kc can be described by using a component related to water evaporation on the soil surface (Ke) and another component related to plant transpiration (Kcb), forming the dual crop coefficient, Kc = Ke + Kcb. In scientific research, separating the components of evaporation and transpiration helps to understand evapotranspiration and contributes to the development of techniques to reduce water consumption by crops. However, in practical situations such as managing irrigation in commercial agricultural crops, the more simplified approach using the single Kc is sufficient [27].

From the experimental records, it was possible to estimate the approximate initial Kc at 0.31 by the L method and at 0.24 by the PM method (Figure 4). In the PM approach, the Kc increased until 825 ADD, reaching 0.66. In the second stage, the Kc increased until 1018 ADD, reaching 0.84 in the L approach. After that, Kc values stabilized and remained the same until the end of the strawberry cultivation cycle. It obtained lower Kc values for the PM approach due to the overestimation of ETo by this methodology. This is due to the lower performance of the method in estimating ETo inside greenhouses [57]. The greenhouse microclimate environment has nearly zero wind speed and low radiation, causing problems for the PM method in the estimation of ETo. There was also a better fit of the regression equation in the L approach, with higher values of R² and lower errors (RMSE).

Allen et al. [11] suggest for strawberry crop the initial, mid-season and late-season Kc values of 0.40, 0.85 and 0.75, respectively. This recommendation is used for strawberry grown under optimal conditions, without water stress, without pests and diseases, with excellent fertility and considering ETo calculated by the PM method. The Kc curve presents itself as the upper limit to the Kcb curve, with differences during the initial and development stages, because of the periodic oscillation in soil moisture content.

3.4. Kc Estimation by NDVI

Using the portable sensor for agricultural use GreenSeeker, readings of the normalized difference vegetation index (NDVI) were performed for the various conditions in the lysimeters (Figure 5). One of the advantages of the portable sensor is that NDVI can be obtained when cloud cover prevents the acquisition of aerial or satellite images [58], or in protected cultivation. According to Ali et al. [35], NDVI sensors provide rapid acquisition of useful information in decision making for crop management. The NDVI remained with averages of 0.84 for the lysimeter cultivated with grass and 0.12 for the lysimeter with recycled paper mulch without cultivation. As for NDVI in lysimeters cultivated with strawberry, with and without mulch, the values increased as a function of ADD.

The curves obtained with the NDVI readings along the strawberry cycle followed the Kc. According to Martin et al. [58], soil conditions and mulch may interfere with sensor reading while the crop canopy has not yet covered the entire surface. From this information, it is possible to notice the difficulty in defining the changes of intervals for stages I and II, requiring further studies to adjust the Kc.

When comparing the Kc and the GreenSeeker sensor readings, correlations of 0.84 and 0.88 were obtained for the L and PM methods, respectively (Figure 6). Thus, NDVI showed good performance in relation to Kc and similar results have been obtained by Alface et al. [28], Rodrigues et al. [31] and Silva et al. [32]. Alface et al. [28] also state that the spectral reflectance of agricultural crops can provide an indirect estimate of Kc values. This was confirmed by the Kc and NDVI curves in the present study. Therefore, NDVI can be used as an indirect way of obtaining Kc for the conventionally cultivated strawberry or using recycled paper as mulch.

3.5. Agronomic Characteristics

The data related to the treatments that indicated the performance of mulch (SWoP—strawberry without recycled paper mulch and SWiP—strawberry with recycled paper mulch) were subjected to analysis of variance (ANOVA). In the ANOVA (

Table 2. Summary of the analysis of variance and mean data of agronomic characteristics of strawberry cultivated in lysimeters with recycled paper mulch (SWiP) and without recycled paper mulch (SWoP).

Factor	CV 1 (%)	F Test		Types of Mulch
		MS 2	p-Value	SWoP	SWiP
Volume of water (m3 m−2)	11.90	1.20 × 104	0.0010	0.394 a	0.317 b
Number of fruits (fruit pl−1)	15.96	3.53 × 10−1	0.9454	43.58 a	43.17 a
Fresh mass (g fruit−1)	5.12	8.45 × 10−1	0.2207	15.86 a	16.51 a
Yield (kg m−2)	18.08	5.12 × 10−2	0.8623	6.21 a	6.37 a
WP 3 (kg m−3)	38.99	3.90 × 101	0.1243	15.68 a	20.09 a
Waste (fruit pl−1)	11.90	1.25 × 10−1	0.9574	4.75 a	4.83 a

¹ Coefficient of variation, ² mean square, ³ water use productivity. Means followed by the same letter do not differ from each other by Tukey’s test (p < 0.05).

), it was observed that the mulch factor caused an effect only on the volume of water consumed by strawberry, with lower water consumption for the SWiP treatment. The evapotranspiration obtained throughout the cycle was 394 mm for strawberry cultivated without mulch and 317 mm for strawberry cultivated with recycled paper mulch, a reduction of 19.5%. The reduction in water consumption occurred due to the elimination of part of the direct evaporation of water from the soil surface with recycled paper mulch.

For the other agronomic characteristics, there was no effect of mulch (Table 2), although there were different values of water consumption between treatments. However, according to García-Tarejo et al. [25], a higher volume of water in strawberry does not always promote better yields, which was confirmed for these variables and other agronomic characteristics, which showed no significant difference. These results occurred because the experiment was conducted in the lysimeter and in a protected environment, where the various interferences can be controlled and crop and irrigation managements are adequate [24]. In addition, the water saved in strawberry cultivation was that which was not lost by direct evaporation from the soil, due to the presence of mulch. This evaporated water does not participate in any physiological and metabolic processes inside the plant, justifying the non-interference in the agronomic characteristics of the strawberry.

The strawberry water use productivity (WP) increased by 28.1% when the soil was mulched with recycled paper, but this was not enough to cause a statistical difference, possibly due to the high coefficient of variation. The average WP value, considering all treatments, was 17.88 kg m⁻³. This result indicates that an irrigation water volume of 56 liters was required to produce 1 kg of fresh mass of strawberry.

Regarding the fruit waste variable, lower losses were expected for strawberry fruits produced in soil mulched with recycled paper. Under these conditions, the fruits do not come into direct contact with the soil and hence show a lower incidence of diseases and pests. However, the results did not reflect this, possibly because the paper absorbed moisture, causing rot in ripe fruits, which was also observed by Diel et al. [59]. This suggests further studies to develop a recycled paper that is also impermeable.

In contrast to the present study, Silva et al. [60], studying the Italian zucchini crop, found that soil cover with recycled paper promoted better agronomic characteristics in relation to the treatment without mulching. The authors attributed this result to the presence of weeds in the treatment without mulching (conventional system), since the recycled paper successfully suppressed weeds. In the present study, weeds were systematically and rigorously controlled, as the objective was to measure water consumption and crop coefficients of only the strawberry. Therefore, weeds did not harm their growth and development in any cropping system.

At the end of the experiment, the aerial part of the plant was removed by cutting and a 200 mm-diameter probe was inserted on the crown up to a 50 cm depth to evaluate the distribution of the root system in the soil profile every 10 cm. A higher concentration was found in the first ten centimeters, with more than 92% of the root system in this soil layer (Figure 7). One of the factors that led to this concentration was the soil moisture content due to high-frequency irrigation. Gonzalez-Fuentes et al. [56] state that another factor that contributed to the concentration of the root system is the effect of temperature on the soil surface due to the mulch.

In view of this study, the possibility of producing the same number of strawberry fruits using a smaller volume of irrigation water was verified. It was also possible to observe that the use of mulching, despite reducing water consumption, is not capable of increasing strawberry fruit yields. Therefore, more studies need to be carried out to select cultivars with better performance, tolerant to water stress and to reduce the use of soil, which is always a carrier of problems. In this way, the results will directly benefit strawberry growers and the environment.

4. Conclusions

Knowing the evaporation (Ke), basal crop (Kcb) and crop (Kc) coefficients for strawberry is of great importance for irrigation management. In the approach using a lysimeter (L) to calculate ETo, Ke was 0.40 until 1018 ADD and then decreased to 0.39 at 2019 ADD. In the approach using ETo calculated by the Penman–Monteith equation (PM), Ke was constant with a value of 0.285. Regarding Kcb, the L approach had three intervals in which the values ranged from 0.08 to 0.84 and in PM, there were two intervals in which the values varied between 0.05 and 0.72. The initial and mid-season Kc values were 0.31 and 0.84 for the L approach and 0.24 and 0.66 for the PM approach, respectively.

The normalized difference vegetation index (NDVI) showed a high correlation with Kc and hence can be used to estimate this variable in strawberry cultivation.

The use of recycled paper as mulch is recommended in strawberry cultivation. This type of mulch reduces water consumption by strawberry crops and does not alter the agronomic characteristics.