1. Mineral Nutrition & Management Dr. Richard Rosecrance California State University, Chico

2. Productivity & Profitability

3. Outline 1. Nutrient pathways to plants 2. N fertilization efficiency. 3. N budgeting, a method of accounting for tree N demand & sources 4. N fertilizer selection & timing

4. How do nutrients get to the plant roots? 1. 2. 3.

5. Nutrient Pathways to Roots 1. Root interception: Ca, (Zn) 2. Mass flow of water: N, Ca, Mg, S, B, (K), (Zn) 3. Diffusion: P, K, (Zn)

6. Cation Exchange Capacity

7. Nitrate In Groundwater

8. Nitrogen fertilizer efficiency trend in Nebraska Even with these improvements, average N fertilizer uptake efficiency is only about 40% of applied N with average yields of about 10 Mt per hectare. A 2-fold increase is possible!

9. N efficiency 1. Amount & and seasonal patterns of N use by trees 2. N availability from nonfertilizer sources (i.e.irrigation water, cover crops) 3. dynamics of fertilizer N availability 4. relationships between timing, amount of fertilizer, and irrigation water applied

10. Part 1 Concepts of Fertilization

11. Midsummer leaf N Concentrations < 2.3% deficient 2.3 – 2.7% adequate > 2.7% excessive

12. Mid-Shoot Leaf Samples Terminal leaflet on spur leaves leaves

13. When to sample leaves? Seasonal Variation in Leaf- nutrient Concentrations

14. Using Leaf Analysis Results to Adjust Fertilizer Practices If Leaf N > above critical value, fertilizer can be reduced or eliminated for a year without impacting growth & yield (esp. on heavy-textured soils)

15. N Use by the Tree Forms of N absorbed by the tree NH 4+ NO 3- N Uptake -- Greatest between onset of active shoot growth until late stages of nut fill

16. N removal in crop Walnut -40 lbs of N/ton of crop N removal calculators - http://npk.nrcs.usda.gov/

17. Whole Tree N Contents by Organ in Almond. Excavation Date 3/2 0 5/208/299/29 N contents (g) 0 500 1000 1500 2000 2500 3000 roots trunk canopy leaves fruit HarvestHarvest 2/20 Uptake

18. Nitrogen budgeting to determine how much to apply N Losses

19. Nitrogen budgeting to determine how much to apply N Losses

20. Volatilization-N lost directly to atmosphere N in ammonium and urea fertilizers may be released to the atmosphere as ammonia gas. (NH 4+ → NH 3 ) pHs >7.5 ↑ volatilization. Volatilization from fertilizers can be ↓ by rapid incorporation

21. Effect of rainfall on Urea N volatilization losses Rainfall Within days after application N Volatilization Losses, % 0.420 310 0.1 to 0.2510 to 30 0530+ (Fox and Hoffman, Pennsylvania – N on no-till corn)

22. Denitrification 1. soil microorganisms: soil nitrates → N 2. 2. N loss ↑ when soils are warm and wet. 3. Denitrification losses are typically less than 5% but can be higher under low- oxygen conditions

23. Losses with urea Urea has no electrical charge, so it moves readily in the soil with rain or irrigation water. Volatilization losses from urea fertilizers are low if urea fertilizers are incorporated into the soil shortly after application.

24. Nitrate Losses Nitrate fertilizers are generally more costly per unit of nitrogen than are ammonium fertilizers. Nitrate is highly mobile in the soil.

25. Choosing & Using N Fertilizers Su Source: Ca Plant Health Association 2002

26. Worksheet Instructions In order to use the nitrogen budgeting approach you will need: 1. yield data for the past few years 2. irrigation records 3. irrigation water nitrate analyses 4. records of compost/manure applications 5. estimates of cover crop yield and nitrogen content 6. calculator

29. Nitrogen Fertilizer Timing and Placement Nitrogen recovery. Fertilizer recovery is greatest when application coincides with periods of high nitrogen demand by trees

30. Split applications. A good rule of thumb is to apply one- half to two- thirds of the fertilizer nitrogen in spring, so it is available during the main flush of spring shoot growth. The remainder should be applied by later during nut fill

31. Best Management Practices Successful N management delivers enough N to the crop to optimize yield and profitability while ↓ losses to water and air. Everyone wants the nitrogen to end up in the crop. Thus, the best management practices (BMPs) presented here are identified as sound practices from economic, production and environmental viewpoints.