Resource-efficient compact bed plasticulture reduces production risks and sustainably intensifies agriculture

Redesign for sustainable intensification

Conventional plasticulture beds (CONV; 76 cm wide, 20 cm tall) are less than 50% wetted with a single irrigation drip tape, especially in sandy soils²⁹. Wetted coverage is important for drip-applied water, nutrient, and pesticide (chemigation) efficiencies. To compensate for the lack of bed coverage, long irrigation cycles (>1-hr/cycle, 1.6 mm/hr) are used to increase lateral wetting (Fig. 1). Long irrigation cycles lead to water and nutrients leaching from the root zone (0–30 cm), where 98% of the crop roots are located³⁰ (Fig. 1). The two compact bed designs (Supplementary Table 1), COMP1 (61 cm wide, 25 cm tall) and COMP2 (46 cm wide, 30 cm tall), more closely match the drip-wetted area. Improved wetted coverage during the second season (2017–2018) achieved an 18-day reduction (15 cm) in drought stress period for COMP2 from April 19th to May 12th, 2018, the peak growth and fruit set period for tomato. There was a lack of optimum water at 5 cm from the plants in CONV but not in COMP2 (Fig. 2a), which likely weakened plants between 60 and 80 days after transplanting (DAT) and reduced fruit growth³¹. Residence time for irrigation water and accompanying nutrients was increased for COMP2 within the root zone, decreasing leaching from this taller bed design. During both seasons, soil moisture (15 cm) in the CONV beds was significantly higher than the COMP2 beds (Fig. 2b). Soil moisture in CONV beds was also above field capacity, a lower threshold of excess water for saturation stress, for more days than COMP2 beds. Beyond plant water stress, excessive moisture also increases water and nutrients losses from the root zone to groundwater and surface water. In addition to increased leaching of drip-applied liquid fertilizer, excessive water also causes increased dissolution and loss of dry fertilizer that is applied at planting.

Conventional tomato plasticulture uses a wide (76 cm) and short (20 cm tall) bed irrigated with a single drip tape that wets less than half of the bed width. Compact beds (COMP1: 61 cm wide, 25 cm tall; and COMP2: 46 cm wide, 30 cm tall) more closely fit the wetted area. Taller compact beds increase the residence time of water and dissolved nutrients within the plant’s effective root zone (30 cm) and protect the roots from saturation resulting from flooding of the row-middle to result in an increased duration of optimal moisture and retention of nutrients.

a COMP2 beds showed higher soil moisture and more plant available water in the top 10 cm during the peak growth and fruit set period compared to CONV. Moisture within CONV beds was closer to the permanent wilting point (0.034 vol/vol), resulting in drought stress. b When moderate rainfall events (Event 1–12 mm rainfall, Event 2–39 mm, and Event 3–20 mm) occurred near fruit set period, the soil moisture 15 cm below bed surface returned more quickly to field capacity (0.134 vol/vol) in the COMP2 beds (~24 h) compared to CONV beds (85–102 h) and reduced the adverse effects of soil saturation on root hypoxia.

A detrimental effect of plasticulture is the increased impervious area of the farm, resulting in higher volume and peak rate of runoff to cause both in-field and off-site flooding. This runoff increases soil erosion and off-site transport of pesticides, dissolved and particulate nitrogen (N) and phosphorus (P), and microplastics that adversely impact the environment (e.g., algae blooms¹⁸). Return flow of rainfall from the plastic-mulched (impervious) beds into row middles increases runoff and soil saturation and poses challenges to flood control in the watershed, especially from extreme rainfall. CBP reduces runoff volume by 51–76% compared to CONV³² due to the reduced impervious area and expanded area of non-mulched row-middles, increasing infiltration and water storage, and limiting sediment and nutrient exports. Increased runoff and flooding and soil saturation also reduce oxygen concentrations, damaging roots and decreasing disease resistance, ultimately affecting yields^33,34. In-field flooding, a regular occurrence during the growing season, affects tomato yield in as little as 24 h, with permanent damage common in 48 h³⁵. During the second season, COMP2 beds returned from near saturation (0.36 vol/vol) to field capacity (S1: 0.096; S2: 0.13) within 24 h after two moderate rainfall events, while the CONV beds remained above field capacity for more than 72 h (Fig. 2b). In addition, extended periods of flooding and associated saturation in CONV beds occurred between 50 and 60 DAT, close to fruit maturity and harvest, increasing plant stress and susceptibility to soilborne diseases such as the reported Fusarium spp.³⁶. We observed a lower incidence of Fusarium wilt in plants on COMP2 beds (6.7% symptomatic plants) compared to CONV beds (10.7%) during the second season, and this difference was significant (p = 0.04). Thus, abiotic (saturation or drought, Fig. 2) and biotic (Fusarium) stress was reduced in COMP2 beds.

The reduction in bed width decreases the soil volume which could lead to salt burn, a potential tradeoff of CBP. However, the electrical conductivity of the soil near the plant was below the threshold (2.5 ds/m) for salt damage to plant in all treatments in both seasons. Compact beds can reduce nitrate leaching to groundwater as indicated by the nitrate concentration values in soil solution below the root zone (30 cm) were 33–77% lower than CONV in all the four sampling events during the first season (Supplementary Table 3). In one of the sampling events (12/21/2016), the concentration differences were significant (p < 0.03). Additionally, lower soil potassium (K) balance (at planting minus harvest) in COMP2 indicated greater uptake of K compared with CONV within the root zone at 15–30 cm (Season 1) and 0–15 cm depths (Season 2) (Supplementary Table 4). Increased K uptake combined with lower drought and saturation stresses and fusarium wilt contributed to the increased yield in COMP2 for the most desirable, extra-large tomato fruit category (Supplementary Tables 5 and 6), which has a higher market value than smaller sizes. Consistently greater yield for COMP2 in both seasons indicates higher nutrient removal and use efficiency. Overall, CBP provided a more nearly optimal growing environment by collective effects of improved water and nutrient availability and reduced abiotic and biotic stressors.

Synergistic benefits from alternative pesticides

Benefits of CBP can be synergized with more selective pesticides to further improve sustainability. A widely used pesticide for soil disinfestation is the fumigant (FUM; 60% chloropicrin plus 40% 1,3-dichloropropene), which is applied proportional to bed width, i.e., plastic-covered area. Accordingly, narrower COMP2 beds received 40% less pesticide than CONV. With CBP, less hazardous but more expensive, alternative pesticide regimes (ALT) of chloropicrin paired with fluensulfone became economically analogous. For example, the cost (US, 2018 dollar) of pesticide (Table 1) for the ALT regime for COMP1 was $1352/ ha, similar to the CONV (FUM regime, $1354/ha). Additionally, the increased drip-wetted coverage in CBP compared to CONV allows for the application of drip-applied non-fumigant (NOFUM) pesticides (fluensulfone and propamocarb) which have difficulty covering more expansive CONV beds. Applying less toxic pesticides (NOFUM), through the drip tape limits human contact and potential injury to farmworkers and grower’s liability during application since they are applied remotely at water and fertilizer pump station. FUM, by contrast, was injected through chisels mounted on a tractor-driven bedder at bedding. NOFUM enables growers more flexibility because they can plant within seven days after application compared to FUM, which has a 21-day re-entry period. NOFUM is also more selective than FUM, allowing populations of beneficial soil microbes and nematodes to survive³⁷.

Increased microbial diversity affects soil nutrient cycling and health³⁸. The dual strategy of compact geometry (COMP2) and pesticide regime (ALT) positively impacted both soil bacterial and fungal community diversity and composition. The bacterial diversity was significantly greater in COMP beds treated with ALT and FUM, while it had significantly lower fungal diversity compared to NOFUM treatments (Fig. 3). Further, in the COMP beds treated with ALT and FUM, four genera belonging to the phylum Firmicutes were significantly enriched at the 0–15 cm depth. Some of the bacteria in these genera have been found to have plant growth promoting properties³⁹. Additionally, three fungal genera belonging to the phylum Ascomycota, containing Fusarium spp., were depleted in soils treated with ALT and FUM in both CONV and COMP treatments (Fig. 3). This depletion of harmful fungal phylum, combined with the reduced drought and saturation stress in COMP2, reduced the risk of disease incidence observed for both COMP2 (ALT and FUM) treatments.

Heat maps showing changes in the relative abundance of the bacterial and fungal genera found to be significantly enriched or depleted (p < 0.05) in soil samples taken at two soil depths (0–15 cm and 15–30 cm) near transplant and at the end of harvest from conventional (CONV; 76 cm wide, 20 cm tall) and compact (COMP2; 46 cm wide, 30 cm tall) beds treated with pesticide formulations including fumigants FUM (60% chloropicrin + 40% 1,3-dicholorpropene) and ALT (chloropicrin + fluensulfone) in comparison to NOFUM (fluensulfone+ propamocarb) treatment for the second season.

The decreased incidence of Fusarium wilt observed in COMP2 beds was influenced by the increase in the population of root-knot nematode (RKN, Meloidogyne spp.). The pathological complex between the presence of RKN and reduced resistance of plants to Fusarium spp. is well-established⁴⁰. We observed increased FUM application efficiency with reduced bed width during the first season. By the end-of-harvest, root gall ratings, a cumulative measure of RKN damage, were significantly reduced for two bed sizes (COMP1 and COMP2) for FUM (Fig. 4a). The population of RKN decreased with bed width (Fig. 4b) despite receiving up to 40% less FUM, a combined effect of increased height of the fumigated bed and better mixing and coverage of FUM due to reduced bed width. Taller COMP beds required nematodes to travel farther from untreated soils below beds to feed on plant roots, as evidenced by the lower root galling index (Fig. 4a). The use of alternative pesticide regimes alone is an effective strategy for improving soil health and reducing the risk of soilborne pests. Together, COMP2 combined with alternative pesticides resulted in synergistic benefits of reduced pesticide usage while still reducing risks from RKN and Fusarium wilt pathogens.

a Mean root gall index and b root knot nematode (RKN) population at the end of harvest for the first season. Error bars indicate standard deviations. For FUM (60% chloropicrin and 40% 1,3-dichloropropene) treated CONV (76 cm wide, 20 cm tall; Fig. 1) and COMP (COMP1: 61 cm wide, 25 cm tall; COMP2: 46 cm wide, 30 cm tall; Fig. 1) beds, root galling index and nematode count were significantly lower (p = 0.01) for COMP1 and COMP2 beds despite using less pre-plant pesticides than CONV. This significant difference is not seen in the ALT (100% chloropicrin and fluensulfone) treatments indicating that the application method (ALT: drip-applied and FUM: chisel-applied) can increase soil coverage.

Outcomes from dual sustainable intensification strategy

The dual strategy of an optimal growing environment with a compact bed (COMP2) and alternative pesticide regimes (ALT) increased large, high-valued, late-season fruit production during both seasons (Supplementary Tables 5 and 6). Increased late-season yield resulted in higher net benefits (revenue minus costs that varied among treatments) for both seasons (Table 1). For the first season, higher yield for COMP2-FUM and COMP2-ALT combined with reduced plastic and pesticide costs increased net profit by $1266 and $1134/ha, respectively. For second season, COMP2-ALT provided greater net profit ($4462/ha) due to similar increases in yields. For the ALT regime, greater net profit was also observed for the CONV-ALT ($3708/ha). COMP2-ALT produced a greater amount of large, high-value fruit during both seasons, which increased the net benefit by an average of $2798/ha. The increased extra-large, late-season fruit for COMP2-ALT reduces the late-season risk in case of increased sale prices without significant additional inputs beyond crop maintenance (irrigation, fertigation, and herbicide/fungicide).

A consistent benefit of the dual strategy of CBP and ALT is the reduced input costs due to reduced bed width. The use of COMP2-FUM, COMP2-ALT, and COMP2-NOFUM treatments reduced input costs by $536, $403, and $683 per ha, respectively. This reduction occurs regardless of the market price, which is highly variable and dependent on external forces. This consistent decrease in input cost can easily offset the cost of new/modified machinery to make compact beds, a one-time investment of US$2000–20,000. This investment would be paid off in one year for farms larger than 50 ha, typical landholding of farms in North America⁴¹. Adopting the dual strategy helps growers reduce production costs and risks to produce more with less.

Individually or combined, CBP (COMP2) and ALT achieve sustainable intensification to increase the system productivity (yield per unit of fertilizer, water, or plastic). For both seasons, COMP2 treatments (COMP2-FUM and COMP2-ALT) increased N, P, and water productivity by almost 4% compared with the conventional treatment (CONV-FUM) (Fig. 5). COMP2-ALT and CONV-ALT treatments increased N, P, and water productivity by almost 12%. The increased input productivity is especially important for N and P, as they are limiting nutrients for freshwater systems globally⁴². Increased P productivity also helps alleviate predicted global shortage of P fertilizer⁴³.

Comparison of the eight treatments (CONV and COMP) based on six sustainability metrics (water [mm/kg of tomato], nitrogen [kg N/kg tomato], phosphorus [kg P/kg tomato], plastic [kg plastic/ kg tomato], fumigant [% reduction/ kg tomato], and cost [$/kg tomato]) averaged over the two seasons. Larger shaded area indicates higher productivity of the system. The coloration of figures shows the gradient of desirability (red less desirable, green more desirable) for each treatment. The CONV (76 cm wide, 20 cm tall) beds were ranked lower for most categories particularly the plastic and fumigant. The COMP (COMP1: 61 cm wide, 25 cm tall; COMP2: 46 cm wide, 30 cm tall) beds were ranked highest in the water [mm/kg of tomato], nitrogen [kg N/kg tomato], phosphorus [kg P/ kg tomato], plastic [kg plastic/ kg tomato], fumigant [% reduction/kg tomato], and cost [$/kg tomato] categories. The COMP2 beds treated with FUM (60% chloropicrin and 40% 1,3-dichloropropene) and ALT (100% chloropicrin and fluensulfone) were ranked highest for productivity. All bed sizes treated with the NOFUM (fluensulfone and propamocarb) pesticide regime were ranked lowest.

Increased productivity of water, fertilizer (N, P), pesticide, and plastic results in a sustainably intensified production system (Fig. 5) by reducing these inputs to produce the same or higher amount of high-value fresh fruits/vegetables. COMP2 treatments (COMP2- FUM, COMP2-ALT) increased the plastic productivity by almost 15% in the first season, producing more with less plastic. During the second season, COMP2-ALT and COMP2-FUM increased plastic productivity by almost 24% and 11%, respectively, compared with the CONV-FUM treatments. The amount of agricultural plastics and associated waste is a serious concern¹², particularly microplastics in the terrestrial environment. Plastics release greenhouse gases (GHG) into the atmosphere during production, application, removal, and disposal to landfills (or recycling) which directly contribute to global warming. Field burning of plastic is common, but when restricted by law, the plastic is either transported to a landfill ($99/ha, Table 1) or a recycling facility, resulting in additional harmful emissions and a cost to the grower. This cost becomes more important in regions with stricter environmental laws (e.g., California, USA). CBP alone can reduce the carbon footprint by 5% for COMP1-FUM and 10% for COMP2-FUM compared with the CONV-FUM treatment⁴⁴. Further GHG emission reductions are achieved with CBP and ALT due to lower plastic and energy usage, resulting in lessening the plasticulture’s contribution to GHG emissions and plastic pollution.

Overall, the dual strategy of redesigned soil growing environment (CBP) and less toxic pesticide (ALT) maintained or increased yields while reducing inputs and negative environmental impacts. The COMP2-ALT and COMP2-FUM treatments were among the top three ranked treatments (8 = highest/best, 1 = lowest/worst) for each of the six productivity metrics (N, P, % reduction in pesticide, plastic, and water productivity, and cost reduction) shown in the sustainability graphs (Fig. 5). The NOFUM treatments (CONV-NOFUM and COMP2-NOFUM) were the lowest-ranked in all categories besides costs (Fig. 5). The CONV treatments (CONV-FUM, CONV-ALT, CONV-NOFUM) were ranked lower than CBP treatments due to increased inputs of plastics and pesticides necessary for the wider CONV beds. Additional environmental benefits specific to COMP2 treatments include reduced losses of water, nutrients, and pesticides to regional ecosystems from runoff, leaching to groundwater, and carbon emissions⁴⁴.

Economic and environmental benefits from this study have already benefited North American growers. As result of this study, two of the ten largest tomato growers in North America, one of whom participated in this study, have already adopted CBP (COMP1) to reduce inputs and costs, increase system efficiency, and reduce their environmental footprint across the US and Mexico. There have been further reports of growers in the US adopting CBP for other crops such as pepper and watermelon that use high inputs to increase production and meet cosmetic market standards. Growers are further exploring conversion to COMP2 beds due to 60% or more increase in energy, fertilizer, and pesticides costs for 2022 compared 2021⁴⁵. Conversion to COMP2 treatments on 10,000 ha would increase system productivity, especially for energy-intensive inputs, by reducing plastic usage by 220 tonnes and pesticide usage by 2438 tonnes while increasing annual income by nearly $28 million. Approximately 200,000 ha of tomato is planted in North America alone each year⁴⁶. Complete conversion to CBP would result in a 4.4 Mt reduction in plastic usage, a 22.8 Mt reduction in pre-plant pesticide usage, and a $183 million increase in annual income. When scaled up for other plasticulture crops in the US, including cucurbits, peppers, and strawberries on 312,126 ha⁴⁷: the benefits increase to 6.9 Mt less plastic, 35.5 Mt less pre-plant pesticides, and $385 million increased income.

The redesign of plasticulture to CBP can also help minimize some negative impacts of intensive agriculture, moving closer to a sustainable system⁴. Reducing inputs with the redesign and adoption of the dual strategy for sustainable intensification of tomato production will reduce two of the top ten most widely used pesticides globally²¹ and have a positive impact on production and the ecosystem⁴⁸. The cost reduction from CBP may sufficiently incentivize growers to use more costly biodegradable mulches. Fumigants are not currently permitted to be used with biodegradable plastic due to its high permeability; however non-fumigant pesticides are. CBP allows for transitioning to a system that combines non-fumigant pesticides and biodegradable mulch with an added benefit of enhanced soil biodiversity. The redesigned beds allow the plasticulture industry to move towards a carbon-neutral system. Global adoption of CBP will help meet the GHG emission goals necessary to limit climate change⁴⁹. Reduction in carbon footprint may become particularly valuable to growers once ongoing legislative efforts on establishing a carbon credit market in Europe and US become a reality.

CBP increases global food security by mitigating environmental impacts and acting as a climate change adaptation strategy, reducing risks from weather extremes (drought and flooding)⁴⁹. CBP increased root zone soil moisture during dry periods, reducing irrigation withdrawals in water-scarce regions (e.g., Southeast and Southwest US). The increase in global food demand and water scarcity from changing climate⁵⁰ is likely to expand plasticulture globally. For temperate and tropical regions with moderate rainfall, reduced impervious area with CBP will increase in-field storage of rainfall and groundwater recharge while reducing runoff, flooding, and associated soil loss. Irrespective of reduced flooding, taller CBP protect crops by keeping plant roots higher in the bed, reducing saturation stress, associated diseases, and nutrient (e.g., N and P) losses to surface and ground waters. Reduced flooding risk is particularly important as climate change is predicted to increase rainfall intensity⁵¹ and pressure on regional water management systems¹⁷. Reduced energy use and costs to pump irrigation and drainage with CBP make it an economic climate change mitigation measure. The combined reduction by CBP in environmental impacts, risks from pests/diseases, and extreme weather will increase food security and increase the system’s resiliency.

Climate change will likely alter the endemic ranges and disease severity⁵² of common plant pathogens. Projected increases in seasonal rainfall variability and rainfall intensity are likely to increase the risk of water-vectored plant diseases, like Fusarium spp. The reduced in-bed soil moisture and decreased rootzone saturation period with the reduction in Fusarium spp., observed in COMP2 treatments, will act as an additional climate change adaptation strategy for plasticulture. Additionally, higher temperatures seen with climate change will increase nematode reproductive potential and affect the viability of plant varieties genetically resistant to RKN, increasing their risk of infection⁵³. These disease benefits might become more critical as the effects of climate change become increasingly evident, exacerbating the effects of both Fusarium spp. and Meloidogyne spp., two crop stressors with major impacts on the global food production.

Future demand for fruit and vegetables will increase, resulting in additional land conversion, which is detrimental to the surrounding landscape and adjacent ecosystems⁵⁴. CBP allows further system intensification by decreasing row-to-row spacing and using the extra space available to increase plant population (33% for COMP2) without additional land clearing/conversion. Reduced need for agricultural land limits the competition for land associated with deforestation for agriculture and housing which is particularly important in ecologically sensitive, coastal regions such as the Everglades and the Chesapeake Bay watersheds in the US. As the urban areas expand to farmlands, pesticide use is being limited due to health concerns, particularly in peri-urban areas. The use of alternative pesticides can meet these regulations cost-effectively with CBP. Together, CBP with alternative pesticides can sustainably intensify plasticulture where costs are high, restrictions on pesticides exist, or land use conversion has negative economic or environmental consequences.

Evaluation of multiple facets of the plasticulture production system was necessary to determine the complex and interconnected nature of the redesigned CBP systems and evaluate the conventional system’s environmental impacts. Future studies should field-verify these results for other crops (e.g., cucurbits) and soil-climatic regions of the world. Future efforts should also be made to develop bed geometry specific irrigation management to evaluate its water conservation potential. Redesigned plasticulture production system will help improve long-term food security, land use efficiency, and sustainability in a more interconnected economy confronted with the looming challenge of climate change. Our results show that a redesign of the current plasticulture to CBP, developed with soil-water interactions at the forefront, synergized with alternative, more selective pesticide (ALT), increases productivity with sustainable intensification.