At Santa Maria, nitrate nitrogen levels in leachate collected at 8-inch depth on all sampling dates ranged from 12 to 27 parts per million in PAM and untreated plots, which was 52% to 80% greater than those in other treatments . At Somis a similar trend was observed: nitrate nitrogen levels in leachate under PAM and untreated soil were 7 to 22 ppm, which was 80% to 90% greater than those under barley or mulch.These results suggest that barley and mulch can reduce nitrate nitrogen in soil and leachate. Mulch and cover crop act as a barrier to runoff water with dissolved nitrogen and sediment and may retain nitrogen to be used for cover crop growth and for residue and mulch decomposition. Turbidity in first flush of runoff was reduced 5- to 10-fold by all treatments compared with untreated soil at both locations in 2018 . These results were similar to turbidity in grab samples taken in 2017 and 2018 , which suggests that all treatments were effective in reducing waterborne sediments on site. Additionally, 75% to 97% less sediment was collected from passive samplers in all treated post rows compared with those in untreated soil, as shown for March 10, 2018 . Relatively high sediment load in fabric treatment resulted from deposits of soil on top of the fabric during removal of plastic from raspberry beds. Similar to the March 10 rain event, we observed significantly lower sediment levels after other rains in all treated post rows compared with untreated rows . We also observed fewer erosion channels in treated post rows compared with untreated plots at both sites during the trial. Besides the agronomic benefits,grow hydroponic retaining soil in the field is also a good pesticide management practice because soil-adsorbed pesticides will stay in the field and not end up in receiving bodies of water. In a previous study, Mangiafico et al. showed that concentrations of the harmful insecticide chlorpyrifos in runoff were linearly related to sample turbidity. This suggests that retaining waterborne sediments on-site is an effective method for mitigating runoff of this pesticide.

Preventing soil movement with these post row treatments may also reduce the costs of sediment removal from receiving waterways and associated environmental impacts . Phosphorus levels in the first flush of runoff samples were reduced by 24% to 85% in all treatments compared with untreated soil at Somis in 2018, except for PAM on Feb. 27, 2018 . Lack of efficacy of PAM on that date may have resulted from deterioration of the PAM seal due to soil disturbance after PAM application and before runoff sample collection. At Somis in 2016–2017 and Santa Maria in 2018, we observed a similar reduction in phosphorus by all post row treatments compared with untreated soil . Since phosphorus is normally adsorbed to soil particles , reduction in turbidity and phosphorus in runoff samples from treated post rows followed a similar trend. Reducing losses of phosphorus from production fields may help prevent eutrophication in receiving waterways when this micro-element is limiting for algal growth . Since tunnel post rows receive water and retain soil moisture, conditions are favorable for weed growth. At both locations weed barrier fabric provided nearly complete weed control with only occasional weed germination in areas where soil was deposited on the top of the fabric. Application of PAM did not provide control, and weed densities in PAM-treated rows were similar to those in untreated plots. Yard waste mulch provided 81% to 90% weed control at Somis but did not control weeds in two out of three evaluation dates at Santa Maria . Mulch at Santa Maria was much finer compared with the one at Somis, and likely decomposed more rapidly, allowing weed growth. Barley cover crop provided 86% and 42% weed control on two evaluation dates at Somis, but after barley was reseeded, high germination of little mallow occurred . Incorporation of barley during reseeding likely disturbed hard-coated weed seeds sufficiently to break dormancy; however, mallow was controlled before seed production when barley was mowed in spring. Barley cover cropat Santa Maria provided 87% and 43% weed control at two out of three evaluation dates.

At Somis in 2018, we observed 3.5 more volunteer raspberry shoots in post rows with mulch compared with other treatments or untreated plots . Unlike weeds, raspberry shoots were able to penetrate mulch and establish, likely benefiting from the greater soil moisture content under it . These results show that weed barrier fabric, mulch and barley can effectively reduce weed control costs in raspberry tunnel post rows, but greater volunteer raspberry shoot management may be required if mulch is used.To estimate the costs of the barley cover crop, we obtained machine use and labor hours for seeding, raking and mowing from cost studies for raspberry production . Cover crop treatment at 500 pounds per acre costs $29.42 for the treatment area minus the weed control benefit of about $18.60, resulting in the net cost approximates of $10.83 for the treatment, or $59.55 per acre per tunnel period . The amount of weed block fabric required for the experimental plot area was 0.22 roll, priced at $349.31 per roll. Ninety metal pins were used to pin the 1,800–square foot fabric area at a cost of $0.12 per pin. The labor needed for spreading and pinning the fabric in the experiment plot was 1 hour at $15 per hour. Assuming the fabric serves two tunnel periods, only half of the cost of the fabric material is applied to one tunnel period. Fabric also provides 100% weed control in post rows. Therefore, the cost of fabric treatment per tunnel period is $29.66 for the treatment area, or $163 per acre for one tunnel period. The volume of applied yard waste mulch should be sufficient to cover the entire post row with a 2- to 3-inch thick layer. Ninety cubic feet of mulch, priced at $0.56 per cubic foot , was applied to the 1,800–square foot treatment area. Delivery and spreading on flat ground with a front end loader and spreader costs $270 per acre. In cases where smaller equipment is used, it would take more labor — at least a day for two people to spread an acre, as it is a slow process and depends on how well the mulch spreads out in the field. In terms of weed control, mulch controlled 70% of the weeds in post row areas. Mulch treatment cost is one of the highest at $35.07 for the treatment area, or $192 per acre per tunnel period. The PAM product was applied at 2 pounds per acre and was priced at $4.00 per pound. PAM was applied six times per tunnel period; hence, the total PAM cost for this treatment is $1.98 for the treatment area.

The labor cost for applying PAM was calculated at 250 minutes per acre per time at a wage of $15 per hour. Therefore, the PAM treatment cost became $34.96 per post row, or $192.27 per acre. The costs of the treatments in this study were very low: 0.7% to 2.4% of the total cultural costs of raspberry production . This suggests that little investment in soil and runoff management can be cost-effective over time for sustainable plasticulture crop production. As the production and use of engineered nanomaterials grows each year, it becomes increasingly important to understand how these emerging pollutants are transported in the environment and to characterize their interactions with other organisms. Plants are the basis for many terrestrial food webs and are at risk of ENM exposure due to buildup in soils through bio-solid fertilizer application, nanopesticide application, runoff, growing lettuce hydroponically or atmospheric deposition.Understanding how ENMs may affect plant performance, fruit and seed quality, and/or generate cascading effects on plant pollinators or herbivores is therefore essential to create informed policies regarding proper management of ENM use and disposal, in addition to the design of more environmentally benign ENMs. A growing number of studies investigating the uptake and toxicity of ENMs in plants have been conducted in the past decade, and have generally found that both depend strongly on plant species and on the characteristics of the focal nanomaterials. For example, TiO2 nanoparticles have been shown to have a toxic effect in vetch,no effect in wheat seedlings,and a positive effect on both photosynthetic rate and chloroplast viability6 in spinach, although it is unclear how much of this variability is due to the model species tested, the properties of the specific TiO2 nanomaterials used, and the method of exposure . Additionally, particle size has been shown to have large impacts on ENM uptake and distribution patterns in plants, with smaller particles typically being taken up in higher amounts and distributed throughout the plant.Smaller aggregate sizes achieved through surface coatings may be expected to show similar trends, but often the changes in surface charge and functionalization caused by these coatings are more important predictors of behavior than size alone.One aspect of plant/ENM interactions that has received little attention is the influence of abiotic environmental conditions on uptake and toxicity. These include factors such as water and nutrient availability, temperature, soil salinity and pH, and light intensity. Plant performance depends heavily on environmental conditions and may be more or less vulnerable to potential toxic effects under different growth scenarios. This has been shown for several non-nano pollutants. For example, high light intensities resulted in higher concentrations of As and Cd in sunflower and duckweed due to increased transpiration, and a range of unfavorable growing conditions have been found to increase damage from Fe-catalyzed reactive oxygen species in many plant species.

Additionally, it was found in pea seedlings that nutrient stress increased the expression of transporter proteins that, in turn, increase cellular uptake of metals such as Cd.In one of the few previous studies specifically investigating the interactions between abiotic growth conditions and ENM phytotoxicity, Josko and Oleszczuk found that the toxicity of metal oxide ENMs to cress was enhanced under high light conditions and ameliorated at higher temperature. Building further understanding of how these factors affect the uptake and toxicity of ENMs in plants is key to accurate predictions of the overall impact of ENMs outside of the growth chamber or greenhouse and across both crop and wild species. In this experiment, we investigated the uptake, translocation, and effects on growth and physiology of three metal oxide ENMs, CeO2, TiO2, and Cu2, in soil-grown Clarkia unguiculata with different illumination and nutrient levels. C. unguiculata is an annual wildflower often used in ecological and genetic studies, and was selected here for its ease of growth, distinct tissues, and moderate lifespan that would allow for subchronic effects to be detected. Additionally, we used individuals from wild populations with greater genetic variability than crop plants typically used in nanotoxicological studies,which makes this experiment conservative with respect to detecting the effects of ENM exposure on plant uptake and performance. The ENMs we chose are widely used in nanoparticulate form in a number of commercial and industrial products and have release patterns that make them relevant for studies of terrestrial ecosystems.Plant exposure levels were chosen to cover a range of ENM concentrations that we predicted to be environmentally relevant based on previous reports of exposure modeling and detection for CeO2 and TiO2. CeO2 has been predicted to be present at levels up to about 1 mg/kg in roadside soils due to atmospheric deposition,and while there are no direct measurements of soil TiO2 concentrations of which we are aware, Kiser et al.found TiO2 in wastewater treatment plant solids at concentrations ranging from 1 to 6 mg kg 1 , which are spread on agricultural fields for fertilizer. The Cu2 ENM used here is an agricultural biocide and is recommended by the manufacturer for use at application rates of up to 18 g m 2 per season.Over spray of this pesticide may have an impact on the surrounding vegetation. We formulated several hypotheses to guide our investigation. First, we hypothesized that ENMs would be found in highest concentrations in the roots as the point of uptake, followed by leaves as the end point of transpiration, then stems as an intermediary between the two. Second, we also predicted that plants grown in high light would uptake and accumulate higher concentrations of ENMs in leaves due to higher rates of transpiration.Third, we hypothesized that P would be positively correlated with ENM concentration in tissues due to sorption of phosphate from the soil.