INTRODUCTION

Global strawberry production totals 4.8 million tons, with the primary producers being China and the United States (^{Minagricultura, 2021}). In 2020, China stood as the leading strawberry producer globally, generating 3,326,816 t (accounting for 37.5%), followed by the United States of America which produced 1,055,963 t (making up 11.9% of global production) (^{Axayacatl, 2021}). In Colombia, Cundinamarca is the leading strawberry-producing department, accounting for 51% of the total land devoted to strawberry cultivation in 2020. It is followed by Boyaca and Cauca, each with a 10% share, and Norte de Santander, which comprises 8% of the cultivated area (^{Minagricultura, 2021}).

Strawberry cultivation occurs in two primary ways, open-field and controlled conditions. Firstly, open-field cultivation faces various biotic challenges, such as infestations by pests like mites, thrips, and lepidopteran larvae (^{Mossler, 2010}). Diseases, primarily caused by the phytopathogen Botrytis cinerea commonly known as "gray mold" can lead to significant losses. These losses can be as high as 25% during the main harvest and 37% during the second production peak (^{Ceredi et al., 2009}). Other diseases such as powdery and downy mildew, anthracnose, and leaf spot can cumulatively result in up to 70% of production losses (^{Rubio et al., 2014}). In Colombia, specifically, diseases constitute the principal reason for crop losses in strawberries. According to ^{Cano (2013)}, the most detrimental rot is caused by Botrytis cinerea, which significantly hampers strawberry production due to its frequent occurrence, leading to more than 50% production losses (^{Álvarez-Medina et al., 2017}; ^{Álvarez et al., 2018}).

As for abiotic factors, limitations arise from exposure to adverse weather conditions, including high levels of rainfall, the mechanical impact of hail, frost, and strong winds. Secondly, under controlled conditions, strawberry cultivation faces the challenge of high infrastructure costs, such as those for greenhouses, and a low cost-benefit ratio. Therefore, many strawberry farmers globally opt for macrotunnel technology, attributed to its lower costs (^{Lamont, 2009}), ease of installation, adaptability to various topographic conditions, and the longevity of some designs, which can last up to 10 years (^{Flórez and Mora, 2010}; ^{Salamé-Donoso et al., 2010}). ^{Rubio et al. (2014)} reported that the utilization of macrotunnels minimizes fertilizer leaching and reduces the volume and frequency of pesticide and fungicide applications. Additionally, it elevates the ambient temperature by 2 to 5°C, thereby hastening the onset of production and providing protection against mechanical damage from precipitation and frost (^{Lamont, 2009}).

^{Rubio (2014)} suggests that further research is needed to explore the impact of macrotunnels on strawberry production, considering various agroecological zones, varieties, and cultivars. Moreover, diversifying production systems like incorporating plastic mulch and microbial consortia for integrated crop management could be viable solutions for enhancing crop sustainability.

In the realm of integrated crop management, numerous studies have demonstrated the effectiveness of bacterial strains such as Bacillus subtilis, B. pumilus, Azospirillum brasilense, and Saccharomyces cerevisiae. These strains not only inhibit the growth of phytopathogenic fungi but also positively influence the growth and development of strawberry plants (^{Cano, 2013}; ^{Mendoza-Léon et al., 2019}).

Conversely, there exist physical barriers designed to prevent fruit from coming into contact with the soil. Such barriers include the use of plastic mulch and production in enclosed environments like macrotunnels, which aim to mitigate the impact of rainfall on disease propagation (^{Calderón et al., 2013}). In this context, mulching stands as a critical component in strawberry production. It offers multiple advantages over bare soil, including early harvests, higher yields, and the maintenance of moisture levels conducive to plant development (^{Calderón et al., 2013}). Soil covers further contribute to plant health by preventing the emergence of weeds and excess moisture on the soil surface, thereby ensuring the cleanliness and quality of the fruit (^{Calderón et al., 2013}).

Owing to the limited availability of technical and economic data on the integrated management of strawberry crops that incorporate bacterial consortia and agroplasticulture techniques like plastic mulch and macrotunnels, this study was conducted. The objective was to evaluate both the technical and economic aspects of using microbial consortia in conjunction with plastic mulch and macrotunnels.

MATERIALS AND METHODS

The study was conducted at the Tesorito farm, affiliated with the University of Caldas, situated in the municipality of Manizales in the Department of Caldas, Colombia. The farm is located at an elevation of 2,340 m a.s.l., with a mean annual temperature of 17.5°C, a relative humidity of 78%, an annual rainfall of 2,000 mm, and 1,473 h of sunshine per year (^{Cenicafe, 2022}). The soil is classified as Andisols, originating from volcanic ashes, and has a sandy-loam texture rich in organic matter.

Two production systems served as the experimental setting. The first was a macrotunnel covering an area of 494 m², measuring 6,50 m in width, 40 m in length, and 7 m in height. Inside the macrotunnel, four beds each measuring 40 m in length and 1,20 m in width were arranged randomly for the study. Plastic mulch with a 1,2 caliber with 30 microns was used. The second system was an open field that also utilized four furrows, each 36 m long and of the same width as in the macrotunnel system. Strawberry seedlings of Sabrina variety were planted at 40 cm intervals between plants, forming two rows per bed. Each production system had a total of 512 plants for evaluation, amounting to 1,020 plants in total.

The study utilized a split-plot experimental design within a randomized complete block arrangement. The main plot represented the production systems (open field and macrotunnel), while subplots were designated based on the use of plastic mulch (with and without). The smallest plot focused on different bacterial consortia treatments commercial: (a) a control, corresponding to conventional farmer management; (b) Bacillus subtilis; (c) Consortium 1, consisting of a mixture of humic acids, Rhodopseudomonas palustris, Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus licheniformis; and (d) Consortium 2, composed of Azospirillum brasilense, Azotobacter chroococcum, Lactobacillus acidophillus, and Saccharomyces cerevisiae. Each experimental unit comprised four plants, and each treatment was repeated four times. Applications were at a dose of 5 cm³ L^-1 of water, equating to inoculated rate of 200 mL of bacterial suspension according to the treatments and concentrations described in the experimental design. It is applied to the soil at the time of crop establishment and two more applications with an interval of 25 d each. For a total of three applications in the crop cycle (first year).

To analyze production costs, agronomic labor records were maintained, and efficiency metrics were calculated based on the time spent on each task. Costing was done based on prices quoted in Manizales, Caldas, during the first quarter of 2023. These market prices served as a reference for calculating the benefit-cost ratio (B/C ratio), which was estimated using average regional market prices per kilogram over the past three years (2021, 2022, and 2023).

For estimating production costs, the study adhered to the concept of 'operational cost' as defined by ^{Herrera et al. (2015)}, which encompasses all costs of production except for interest on invested capital. This approach allowed for the calculation of production costs and cash flows, providing a basis for profitability estimation targeted at the local market.

Production cost data were recorded in a spreadsheet adapted from the Colombia International Corporation model (^{DANE, 2023}). All figures were converted to U.S. dollars per hectare (US$ ha^-1), using the exchange rate reported for the first quarter of 2023 by the Banco de la República de Colombia.

In these cost estimates, a consistent technological level was maintained, along with the proportionality of manual labor hours and input quantities. Technical coefficients -such as man-day hours and input amounts- were based on the work efficiencies observed at Tesorito farm. Costs were bifurcated into two categories:

Manual operations: These were estimated at an average rate of US$16.20 per man-day. This figure reflects the wages paid to rural workers in the region and does not include contributions to social security. Generally, this work is performed either by family members or by labor hired for specific seasons.

For calculating input costs, we relied on the average pricing from major regional distributors. Subsequently, production costs were divided into initial establishment costs in the first year and maintenance costs in the second year, as detailed in table 1. Cash flow projections spanned a 24-month investment period, with all values presented in US dollars per hectare. Additionally, the construction and annual operational costs for the macrotunnel system, covering an area of 540 m², are itemized in table 2.

Profitability analyses included the calculation of several key financial indicators: gross income, net income, production costs, and unit-specific economic measures such as the Unit Production Margin (MUP) and the Benefit-Cost Ratio (B/C).

To evaluate yield, variables such as per-plant fruit weight, per-plant production in grams, gross yield in kg ha^-1, and net yield in kg ha^-1 were assessed weekly for two years. Statistical evaluation was conducted using analysis of variance (ANOVA) through the SAS software package, version 9.3 (^{SAS, 2013}). Further, Duncan's test was employed to conduct comparative mean tests at a 5% significance level.

RESULTS AND DISCUSSION

The first-year production costs for a hectare for all treatments of strawberry cultivation totaled on average US$36,913 with inputs comprising 59.33% of the total costs. Specifically, seed costs accounted for 46.09% of these input costs. Importantly, we acknowledged the rising cost of agricultural inputs in recent ten years, which has a significant impact on production.

In the second year, a cost reduction of 60.61% was observed for all treatments, amounting on average to US$14,538.12 per hectare. Crop work constituted the majority of these costs at 71.88% (Tab. 1). Noteworthy cost fluctuations were attributed to material and labor expenses, particularly those linked to the installation of plastic mulch, weed management, and harvesting activities. These variations were in line with the crop's variable productivity. Additionally, the macrotunnel system incurred a one-time construction and installation cost of US$51,205 and an annual operational cost of US$6,731.18 (Tab. 2).

In a study carried out by ^{Rubio et al. (2014)}, it was determined that the crop preparation and establishment phases required less labor in both macrotunnel and open-field systems when compared to crop maintenance activities. Moreover, establishment activities under macrotunnels required more labor compared to open fields due to the necessity to install supportive poles and assemble the macrotunnels. The labor cost for the construction of the macrotunnel in that study was US$70.3, compared to the US$117.91 in our study, thereby highlighting the increase in labor costs from 2014 to 2023. According to ^{Rubio et al. (2014)}, they found that growers invest in macrotunnels due to their low cost and long useful life. This is particularly noteworthy when considering that losses caused by B. cinerea disease are greater in open fields than under macrotunnels. This represents a higher cost in terms of management, making the semi-controlled system a viable option for strawberry production.

CONCLUSION

The interaction of the macrotunnel production system combined with plastic mulch and utilizing bacterial consortium 2 yielded the highest gross and net yields of 25,041 and 17,330 kg ha^-1, respectively. With a favorable cost-benefit ratio of 1.41 in the second year, this approach proves to be a sustainable alternative for growers in the study area.

Additionally, using the macrotunnel production system resulted in a 35.71% reduction in losses when compared to the open-field system.