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  • Author or Editor: David W. Studstill x
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The quantitative assessment of nitrate-nitrogen (NO3-N) leaching below the root zone of vegetable crops grown with plasticulture (called load) may be done using deep (150-cm) soil samples divided into five 30-cm long subsamples. The load is then calculated by multiplying the NO3-N concentration in each subsample by the volume of soil (width × length × depth, W × L × D) wetted by the drip tape. Length (total length of mulched bed per unit surface) and depth (length of the soil subsample) are well known, but W is not. In order to determine W at different depths, two dye tests were conducted on a 7-m deep Lakeland fine sand using standard plasticulture beds. Dye tests consisted in irrigating for up to 38 and 60 hours (11,756 and 18,562 L/100 m of irrigation, respectively), digging transverse sections of the raised beds at set times and taking measurements of D and W at every 30-cm. Most dye patterns were elliptic elongated. Maximum average depths were similar (118 and 119 cm) for both tests despite differences in irrigation duration and physical proximity of both tests (100 m apart in the same field). Overall, D response (cm, both tests combined) to irrigation volume (V) was quadratic (Dcomb.avg = –2 × 10–7V2 + 0.008V + 34), and W responses (applying maximum and average values, Wmax and Wmean) to D (cm) were linear (Wmax = –0.65D+114: Wmean = –0.42D + 79). Predicted Wmax were 104, 84, 64, 44, and 25 cm at 30-cm depth increments. These preliminary values may be use for load calculations, but are likely to over-estimate load as they were determined without transpiring plants and may need to be adjusted for different soil types.

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