Reducing Unavoidable Nutrient Losses from Horticultural Crops. Sanjay Shukla Brian Boman Bob Ebel Ed Hanlon Pam Roberts SWFREC and IRREC UF/IFAS

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1 Reducing Unavoidable Nutrient Losses from Horticultural Crops Sanjay Shukla Brian Boman Bob Ebel Ed Hanlon Pam Roberts SWFREC and IRREC UF/IFAS

2 Unavoidable Leaching Losses Hendricks et al., 2007

3 Unavoidable Leaching Losses Nutrients below the root zone Normal leaching Leaching after a high rainfall event Groundwater to surface water (drainage) Nutrients in runoff After a rainfall Hydrologic settings Plant Uptake Leaching Runoff Precipitation Surface storage

4 Managing Unavoidable Leaching Losses Optimize water and nutrient retention In-field Reduce runoff & drainage Farm-scale Store, retain, treat, and reuse the drainage and runoff Watershed-Scale Ag-Urban water storage, banking, and treatment

5 Field-scale Water Retention Reduce the rate and/or volume of drainage and runoff Water table management Soil moisture-based Reduces water use (36%), runoff, and drainage (Pandey et al, 2007) Relationship between rainfall and drainage to water table response ( Water table change = 16 x rainfall) (Jaber and Shukla, 2006) Low and high areas - drainage Impacts on nutrient loadings unknown

6 Field-scale Water Retention Crop Specific Drainage Management Reducing the rate and volume of drainage Flood tolerance of crops (Ebel, 2008) Tomato 24 hrs, Watermelon 4 d; Urban unknown Plant pathogens under different drainage conditions Develop drainage management strategies using water table response to rainfall and drainage, flood tolerance of crops, and pathogen survival

7 Structural Farm-Scale Stormwater Management Control stormwater rate and volume as well as reduce nutrient discharge by physical, chemical, and biological proceeses Detention/Retention Detention: Reduce off-site discharge by temporarily holding water in a storage basin and releasing it slowly Retention: Prevention of discharge through storage (percolation & ET) Tailwater (Drainage + Runoff) Reuse Non-structural Filter strips, summer flooding, ditch management

8 Ditch Water Retention and P Loadings Mesocosm Study SRP Load (mg/m^2) P Retention at Small Ditch Time Elapsed (days) Average Retention: Small : 50 % Large : 16 % Collins (2005) and Shukla et al. (2006) High Spike Control

9 Stormwater Impoundments Stormwater impoundments Onsite detention of the first inch of runoff or the runoff from a 2.5 in rainfall Most citrus and vegetables (and urban landscape) production areas in S Florida

10 Stormwater Impoundments One of the best BMPs > 90% retention of suspended solids Dissolved nutrients low (lack of data) Physical, biological, and chemical processes Water and nutrient dynamics not well understood

11 Hydraulic efficiency Nutrient Treatment Enhancement of Impoundments avoid shortcircuiting impoundments shape (L:W Ratio) Sorption and uptake wetland vegetation biomass harvesting Alternative pump site Discharge Current pump site Shukla and Jaber (2008)

12 Tailwater Recovery and Reuse Collection, storage and conveyance of tail-water (drainage and runoff)

13 Modifications of Impoundments for Reuse Evapotranspiration (4 to 32%) Rain (4 to 29%) umped inflow 71 to 96% Outflow 31 39% subsurface movement 35 to 61%

14 Water Supply from Impoundments Alternative Thickness (in) Description Weeks of irrigation 1 6 Lining entire reservoir 13 6 Lining inside ditch and embankments Lining inside ditch and embankments 4 3 N/A Recirculation 4 Weeks of irrigation based on average weekly use in the grove during the irrigation season Shukla and Jaber (2006, 2005, 2004)

15 Tailwater Recovery and Reuse Water conservation part has been studied CA, NJ, and some work in FL Lack of data on impact on nutrient discharges New Jersey combined with Bioretention, 25% reduction in P losses (Buckley, 2008) Reduction in nutrient discharge expected water volume, fertilizer use N and P in tail-water Treatment to reduce the spread of plant disease (Roberts, 2007)

16 Summer Flooding Flooding during summer fallow period for vegetable production systems potential for reducing water and nutrient (?) discharges from the farm Effects on water and nutrient discharges not known

17 Filter Strips Reduces suspended solids and sediment bound nutrients sediment - 56 to 95% (Leeds et al., 1994) Little effect on dissolved nutrients Effectiveness varies with slope, vegetation, soil type, rainfall and runoff conditions optimum filter strip width 8 to 30 ft Limited data for Florida

18 Ditch Management Periodic cleaning of ditch helps provide adequate drainage Cleanning of light sediment flock material that has high P Accumulation of sediment upstream of drainage structure EAA Study (Diaz et al.,2005) enough P for several years Spoil material should be removed and deposited to a upland site Ditch sumps

19 Watershed-scale Use of agricultural areas to store and treat water Impoundments as a source of alternative water supply (Jaber and Shukla, 2004, 2005, and 2006) Water quantity and quality trading Harvesting water - second crop (Shukla, 2006) Water banking Urban-Ag water transfer

20 Future Research Needs - Field Tools for drainage management under high water table conditions. Reduce the drainage volume, nutrient loadings, and water use. Water table response to rainfall and drainage soil moisture-based drainage management reducing drainage rate and volumes effects on water use, quality, plant disease, and crop production Modifying drainage infrastructure to avoid excessive drainage and increase water retention

21 Future Research Needs - Field Flooding tolerance and viability of plant pathogens for most commonly grown commercial horticultural crops under different drainage scenarios Effects of summer flooding on water & nutrient discharges, disease, and production

22 Research Needs Farm Scale Quantification of water and nutrient (treatment eff) dynamics of stormwater impoundments Identification and evaluation of strategies to enhance the nutrient treatment efficiency of impoundments Increase hydraulic efficiency Soil sorption and plant nutrient uptake Modifications of impoundments for reuse

23 Future Research Needs Farm Scale Tailwater reuse strategies on water and nutrient discharge, crop disease, production, and farm income Effectiveness of ditch management (cleaning and vegetative filter strips) practices on nutrient discharges Effects of cleaning Vegetative filter strips

24 Future Research Needs Watershed Use of citrus and vegetable (and others) impoundments as water harvesting units and strategies for utilizing this water for on-farm irrigation to banking and trading this water with urban communities Effects on watershed-scale flows and water quality Shukla, Borisova, Roka, Hanlon, Roberts, and Main (2008) NRI Proposal