Sustainable Ag Expo November 18, Kristin Dzurella UC Davis Dept. of Land, Air, and Water Resources

Transcription

1 Sustainable Ag Expo November 18, 2013 Kristin Dzurella UC Davis Dept. of Land, Air, and Water Resources

2 Ag s Contribution to Groundwater Nitrate California leads the nation in cash farm receipts, producing ~50% of the U.S. fruits, nuts and vegetables. Agricultural N inputs found responsible for a large majority of the GW nitrate contamination in some parts of CA. Statewide regulations are currently being implemented.

3 Cropland N Sources and Fate Salinas Valley (drawn from Viers et al. 2012)

4 New reporting requirements The Central Coast Water Board regulatory order requires growers deemed at high risk for nitrate leaching to report their total (synthetic and organic) N applications. Some form of nitrogen budgeting likely will be incorporated into the regulations for high leaching risk growers in some areas Pending recommendations from the CDFA Task Force and Water Board Expert Panel on nitrates. N budgeting assists the grower in managing their N inputs. Such educational recordkeeping can act as a performance indicator in terms of nitrogen use efficiency (NUE) over time.

5 Relative Leaching Risk Risk of nitrate leaching beyond the rootzone and into the groundwater is multifaceted Driven by field specific variables and management Definitions of high risk growers vary by region, e.g., currently the CC Order references the UC ANR Nitrate Hazard Index (Wu et al. 2005,

6 Nitrate loss below the rootzone: Example variables (UC ANR Hazard Index, HI) Crop grown Rooting depth N Requirements: Total and uptake rates Harvest time in relation to peak N uptake Fraction of crop top that is harvested Soil characteristics Pedon texture / permeability Infiltration rates / restrictions to water flow Denitrification potential Type of irrigation system Level of operator control, fertigation Not a GW contamination estimation tool: e.g. management, depth to GW, recharge rate not considered these can have large impacts 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Salinas Valley HI Component Distribution Crop Soil Irrigation HI 1 HI 2 HI 3 HI 4 HI 5 Dzurella et al. 2012

7 Budgeting as a Performance Indicator: indirect but easy Terminology Nitrogen Ratio N Inputs/Harvest OR Inputs/Uptake Nitrogen Use Efficiency (NUE) N harvest / inputs, expressed as % Varies significantly between crops depending on how much biomass is exported from the field and other variables Use of BMPs increases N in harvested portion of the crop relative to N inputs

8 Cotton yield N fertilizer applied N content of 1 cotton bale per acre 3.5 bales 150 lb 31 lb* Harvest N removal lb (=3.5 x 31) * Western Fert Handbook, 9 th ed. N Use Efficiency N Input : Harvest N Ratio = = Simple example balance

9 N inputs synthetic fertilizer only N available to the crop includes both fertilizer applications and credits. Must also consider: Nitrate already present in irrigation water: Measure concentration and annualize applications Compost and manure applications: Must estimate N content and mineralization time (which can carry over into the next season) uncertainty and variability Carryover: N in unharvested portions of prior crop critical consideration when growing multiple crops per year, especially following crops in which a large portion of the biomass is left in the field Again, highly variable and estimations can be uncertain

10 Calculating N yield (harvested N) Harvested N content varies depending on multiple factors Book values of N content of harvested crops aren t available for all crops grown in California, lab analysis isn t free

11 Alternative Budgets rather than comparing available N to harvested N Compare available N with N required to reach sufficient yield Adjust high end of typical N rate range down based on inputs / credits More intuitive for growers, but typical N rate range can be subjective Question: What is crop N need and how is this and typical range determined? Does need refer to uptake/consumption or an application rate range?

12 Nitrogen need =? Growers and many published guidelines: Range of N applications needed to reach expected yield Ranges often large as they depend on site specific factors and some level of subjectivity Regulators: Range or average of whole-plant N uptake Problem: whole-plant N uptake data is relatively sparse - What is ultimately required depends on outcome of task force and expert panel, but a ratio based on harvested N reduces above uncertainties - Budgeting is a planning tool and using results as a yardstick for efficiency is most informative over a period of years

13 Summary Sustainable N management paramount: Ag s impact on groundwater nitrate contamination and public health cannot be ignored Although N budgeting may become a record-keeping requirement, the real focus should be on increasing efficiency through implementation of Beneficial Management Practices (BMPs) Budgets only focus on N application rates: proper N application timing, placement, and source, as well as careful water management have large impacts on reducing leaching losses and GW contamination Budgets don t increase NUE and WUE: BMPs do.... Match supply with demand BMPs are site specific: Effectiveness, feasibility, appropriateness depend on field specific variables

14 Thank you