1. Management Practices and Nitrogen Availability for Organic Vegetables Grace (Guihua) Chen University of Maryland, Dept. of Entomology Contact: gchen2@umd.edu, 301-405-3945

2. Potential N Deficit Potential N Loss Challenges to Synchronize Plant Available N with Crop N Demand A. Rapid N release fertilizers B. Slow N release fertilizers PAN Crop N demand PAN Plant Available N (PAN) = Mineral Nitrogen (N min ) (N-NO 3 - & N-NH 4 + ) in the soil

3. Time (day) Slow growth Maximum leaf area Rapid linear growth Maturity Maximum Biomass accumulation Cumulative biomass (tons/A) Cumulative biomass Crop Growth and Total N demand Cumulative N uptake (lb/A) Phase I: Slow N uptake Phase II: Rapid N uptake Phase III: N redistribution (slow or no uptake) Maximum N uptake (Sullivan, et. al., 1999. Oregon State)

4. Time (day) Slow growth Maximum leaf area Rapid linear growth Maturity Maximum Biomass accumulation Cumulative biomass (tons/A) Cumulative biomass Crop Growth and Daily N demand Daily N uptake (lb/A) Maximum N uptake rate Period of rapid N uptake (Sullivan, et. al., 1999. Oregon State)

5. Question How to make soil available N matches with my crop N demand?

6. Atmospheric N Nitrification Mineralization Immobilization Atmospheric fixation and deposition Animal manure and biosolids Plant residue Biological fixation Organic N Ammonium N (NH 4 + ) Leaching Denitrification Volatilization Runoff Erosion Commercial fertilizers Nitrate N (NO 3 - ) Plant Uptake Crop harvest N input N loss N component The Nitrogen Cycle

7. Conditions Controlling Organic N Mineralization and Immobilization  Sources of organic fertilizer: Carbon to nitrogen ( C:N ) ratio  Soil moisture and Temperature  Tillage: Changes in soil moisture, temperature and placement of fertilizers Sources of organic fertilizer: Relationships between C:N Ratio and N mineralization

8. C:N Ratio and N Mineralization Rate (R. Flynn, 2008, New Mexico State University) Percent of total N mineralized (Plant Available N) after 4 weeks at Temp= 72 ⁰ F)

9. C:N Ratio and N Mineralization Rate (Based on data from R. Flynn, 2008, New Mexico State University) Relationship between C:N ratio and PAN after 4 weeks (T = 72 ⁰ F)

10. 5:1 10:1 15:1 20:1 30:1 40:1 Clovers Peas Radish Canola Cereal rye, triticale Annual ryegrass Oats C:N Ratio High N content Low N content N mineralization Microbes release excess N to soil N Immobilization Microbes tie up N from soil Neutral Mineralization Immobilization C:N Ratio of Cover Crops Residues and N Mineralization / Immobilization (C. White, 2014. Penn State Univ.) C:N Ratio and N Mineralization Rate

11. (Source: D.M. Sullivan and N.D. Andrews, 2012, Oregon State Univ.) C:N Ratio and N Mineralization Rate Tiller Joint Boot Cereal 3/1 4/1 5/1 6/1 Vegetative Bud Legume 75% legume 25% legume Date of cover crop termination PAN from cover crop (lb/A) When to terminate my cover crops?

12. (USDA NRCS East National Technology Support Center, Greensboro, NC) Recommendation: Grab some soil samples from your field before planting/transplanting to test %N and C:N ratio

13. Conditions Controlling Organic N Mineralization and Immobilization  Sources of organic fertilizers:  Soil moisture and Temperature  Tillage: Changes in soil moisture, temperature and placement of fertilizers Soil Moisture and Temperature?

14. Effects of Temperature on N Mineralization Soil water content at A. 60% field capacity B. 80% field capacity C. 100% field capacity Incubation time (days) Mineralized N (mg kg -1 ) (Guntiñas et al., 2012. Eur. J. Soil Biol.) Increasing soil temperature increases N mineralization rate 120 100 80 60 40 Moisture (% field capacity) T = 35 ⁰ C T = 10 ⁰ C Q10 8 6 4 2 0

15. Effects of Soil Moisture on N Mineralization Mineralized N (mg kg -1 ) Incubation time (days) A. T = 20 ⁰C B. T = 25 ⁰C C. T = 30 ⁰C 60% FC 80% FC 100% FC Water content at No clear clue of mineralized N with changes in moisture (Guntiñas et al., 2012. Eur. J. Soil Biol.)

16. Conditions Controlling Organic N Mineralization and Immobilization  Sources of organic fertilizers:  Soil moisture and Temperature  Tillage: Changes in soil moisture, temperature and placement of fertilizers Tillage Effects?

17. Tillage Increases N Mineralization Rate Mineralized N from periodically sampled field soils (Chen, et al., unpublished data, the project funded by USDA-NIFA ORG program)

18. Tillage Effects on PAN and Crop N Demand PAN 1.PAN matched eggplant N demand 2.Potential N loss in CP and ST in early growing stage? (Chen, et al., unpublished data, the project funded by USDA-NIFA ORG program)

19. Summary 1.Know your crop: the critical period of N uptake and total N demand 2.Know the C:N ratios of your fertilizers 3.Make the right decision: Matching crop N uptake pattern with N release pattern from the fertilizers Low C:N ratio fertilizers : a)low rate at planting (or no application if you have legume cover crops) b)Moderate to high rate at side-dressing High C:N ratio fertilizers : a)High rate at planting b)Applying fertilizers of low C:N ratio may be needed at rapid N uptake period 4. Practice strip-till and No-till: a)ST has higher yield potential and same N mineralization rate as CP b)Less soil disturbance (from ST and NT) increases your soil organic N pool and productivity