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Mineral Nutrition & Management. Dr. Richard Rosecrance California State University, Chico. Productivity & Profitability. Outline. Nutrient pathways to plants N fertilization efficiency. N budgeting, a method of accounting for tree N demand & sources N fertilizer selection & timing.
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Mineral Nutrition& Management Dr. Richard Rosecrance California State University, Chico
Outline • Nutrient pathways to plants • N fertilization efficiency. • N budgeting, a method of accounting for tree N demand & sources • N fertilizer selection & timing
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)
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!
N efficiency • Amount & and seasonal patterns of N use by trees • N availability from nonfertilizer sources (i.e.irrigation water, cover crops) • dynamics of fertilizer N availability • relationships between timing, amount of fertilizer, and irrigation water applied
Midsummer leaf N Concentrations • < 2.3% deficient • 2.3 – 2.7% adequate • > 2.7% excessive
Terminal leaflet on spur leaves Mid-Shoot Leaf Samples
Seasonal Variation in Leaf-nutrient Concentrations When to sample leaves?
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)
N Use by the Tree • Forms of N absorbed by the tree • NH4+ • NO3- • N Uptake -- Greatest between onset of active shoot growth until late stages of nut fill
N removal in crop • Walnut -40 lbs of N/ton of crop • N removal calculators - http://npk.nrcs.usda.gov/
Whole Tree N Contents by Organ in Almond. 3 0 0 0 H a r v e s t 2 5 0 0 2 0 0 0 Uptake N contents (g) 1 5 0 0 r o o t s 1 0 0 0 t r u n k c a n o p y 5 0 0 l e a v e s f r u i t 0 0 2/20 5 / 2 0 8 / 2 9 9 / 2 9 3 / 2 E x c a v a t i o n D a t e
Nitrogen budgeting to determine how much to apply • N Losses
Nitrogen budgeting to determine how much to apply • N Losses
Volatilization-N lost directly to atmosphere • N in ammonium and urea fertilizers may be released to the atmosphere as ammonia gas. (NH4+→ NH3) • pHs >7.5 ↑ volatilization. • Volatilization from fertilizers can be ↓ by rapid incorporation
Effect of rainfall on Urea N volatilization losses (Fox and Hoffman, Pennsylvania – N on no-till corn)
Denitrification • soil microorganisms: soil nitrates → N2. • N loss ↑ when soils are warm and wet. • Denitrification losses are typically less than 5% but can be higher under low- oxygen conditions
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.
Nitrate Losses • Nitrate fertilizers are generally more costly per unit of nitrogen than are ammonium fertilizers. Nitrate is highly mobile in the soil.
Choosing & Using N Fertilizers • Su Source: Ca Plant Health Association 2002
Worksheet Instructions In order to use the nitrogen budgeting approach you will need: • yield data for the past few years • irrigation records • irrigation water nitrate analyses • records of compost/manure applications • estimates of cover crop yield and nitrogen content • calculator
Nitrogen Fertilizer Timingand Placement • Nitrogen recovery. Fertilizer recovery is greatest when application coincides with periods of high nitrogen demand by trees
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
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.