Fertilizer Grade Is the percentage composition of fertilizer with respect to N, P (as P 2 O 5 ), and K (as K 2 O) For a fertilizer grade of 15-25-10 means the fertilizer is: 15% N 25% P 2 O 5 (also called “available phosphoric acid” or “phosphate”) 10% K 2 O (also called “potash”)
Conversions K 2 O to K: K=39 K 2 =78 O=16 K 2 O=9478/94=0.83 So K 2 O x 0.83 = K P 2 O 5 to P: P=31P 2 =62 O=16O 5 =80 P 2 O 5 =14262/142=0.44 So P 2 O 5 x 0.44 = P
Factors to Consider When choosing a fertilizer application method, the following should be considered: Crop root zone Soil chemical/physical properties Fertilizer properties Nutrient mobility Soil Moisture Irrigation method, frequency System limitations
Placement Methods Topdressing - Solids or liquids Broadcast Band Injection - Solids or liquids Called side-dressing when applied to growing plants Starter fertilizer is applied at planting time Fertigation Foliar
Applying fertilizers in irrigated systems: 1.Apply fertilizers either in the area of maximum root density, or where water will move it toward roots. 2.Keep nutrients within crop root zone, prevent leaching. 3. Consider nutrient mobility.
Broadcasting Things to think about when broadcasting fertilizer Best for soluble, mobile fertilizers Results in a more or less uniform fertilizer distribution Band applications can be more efficient because __________________________. Do not broadcast NH 4 + fertilizers on alkaline soils unless immediately incorporating. nutrients are placed near root zone
Broadcasting Broadcast TSP followed by “listing” (making beds) Maricopa, AZ
Broadcasting Slow-release fertilizer broadcast under microsprinkler-irrigated navel orange, Waddell, AZ
Broadcasting - gypsum and lime are almost always broadcast Gypsum broadcast on pecans, Kansas Settlement, AZ
What can be broadcast? Solid inorganic fertilizers Slow-release fertilizers Non-volatile liquid fertilizers Organic fertilizers Lime/gypsum
When is broadcasting appropriate? When surface losses of NH 3 are not likely. With highly soluble fertilizers when erosion losses are not likely When soil disturbance is not desirable Turf No-till Alfalfa Permanent crops (apples, pecans, olives, etc.) When treating bulk soil properties Lime, gypsum
Band (injection) Application Can be applied on or below (injection) the surface. Useful for solids, liquids, or gases. Results in a localized zone of nutrient distribution – good for nutrient tied up by soil. With at-planting applications, salt damage to seedlings can be a problem. When side-dressing, root damage can occur.
Band Application Surface band near transplanted broccoli, sprinkler-irrigated Oregon “Side-dressing” lettuce with liquid N fertilizer, Yuma
Band Application http://www.noble.org/Press_Release/Ag/Bandin gFertilizer/PlacementTube.jpg http://www.yetterco.com/PressRelease/TheLea dingEdge/2004-07-20/2004-07-20c.jpg
Band Application Banded zinc application on pecan trees. Sahuarita, AZ
What can be band-applied? Solid inorganic fertilizers (subsurface) Liquid fertilizers (surface or subsurface) Gas (NH 3 ) must be applied subsurface Organics (some problems here)
When are band applications appropriate? Almost any time, except when root disturbance would be excessive. Therefore, most appropriate in early season before complete development of root system. With immobile nutrients. Where nutrient losses or fixation are likely.
Fertigation The application of fertilizer with irrigation water. Can be used with any irrigation method. Will result in uniform or localized nutrient distribution, depending on irrigation method Effectiveness of distribution depends on irrigation uniformity Water quality is important, especially in drip systems!!!
Fertigation Fertigation of liquid N fertilizer onto flood-irrigated durum wheat Maricopa, AZ
Consequences of Mixing Incompatible Chemicals H 2 SO 4 + Ca(NO 3 ) 2 CaSO 4 + HNO 3 CaSO 4 If these chemicals were improperly injected together into an SDI system, plugging of emitters and irreversible damage would result.
What can be applied by fertigation? Most liquid fertilizers Compatibility with irrigation water is of the utmost importance in pressurized (low-flow) irrigation systems. Efficiency of nutrient application will depend upon efficiency of water application.
When is fertigation appropriate? In irrigated systems In low-flow systems (i.e. drip or microsprinkler) any time. In flood irrigation systems, fertigation is most appropriate later in the season when root system is well-developed fertigation is used with permanent crops In greenhouses
Foliar Applications Foliar applications are most useful for: Applications of micronutrients, especially to alkaline soils Applications at specific times (e.g. flowering) It is difficult to apply enough N or K through a foliar application to supply plant needs without burning. Nutrient concentrations in liquid should be <1-2% to prevent burning.
http://www.omafra.gov.on.ca/english/crops/hort/ news/hortmatt/2005/12hrt05a3.htm Plants are easily damaged by foliar applications - damage from cytokinins in foliar seaweed fertilizer on ginseng.
Preplant Can be topdressed, with or without incorporation, or injected. Should be based on a preplant _____________. At-planting Usually injected with or near the seed “Pop-up” or “starter” application Post-planting Usually injected or fertigated, can be topdressed “Side-dressing” Timing of Fertilization soil test
Pre-plant Fertilization Best for: Applications of P and/or K in the event of low soil test values Applications of NH 4 -N in the event of a low soil test value (not too far in advance) - Can cause salt damage
Special Case - Band applications at planting Placed with seed is called “pop-up” “Starter” fertilizer often applied “2x2”
At-planting Fertilization “Pop-up” fertilizers are applied with the seed. Amounts of N and K (highly soluble fertilizers) should be limited to prevent seedling damage “Starter” fertilizers are usually applied a short distance from the seed Less danger from salt damage Excellent way to ensure good seedling vigor
Fertilizer Salt Index Fluid Journal Spring 2001 Materials and analysis Salt Index per equal weights of materials per unit of nutrients 1 Nitrogen/Sulfur Ammonia, 82%N 47.10.572 Ammonium nitrate, 34%N104.03.059 Ammonium sulfate, 21%N, 24%S 68.33.252 Ammonium thiosulfate, 12%N, 26%S 90.47.533 Urea, 46%N 74.41.618 UAN, 28%N (39% NH 4 NO 3, 31% urea) 63.02.250 32%N (44% NH 4 NO 3, 35% urea) 71.12.221 Phosphorus APP, 10%N, 34%P 2 O 5 20.00.455 DAP, 18%N, 46%P 2 O 5 29.20.456 MAP, 11%N, 52%P 2 O 5 26.70.405 Phosphoric acid, 54%P 2 O 5 1.613 2 72%P 2 O 5 1.754 2 Potassium Monopotassium phosphate, 52%P 2 O 5, 35%K 2 O 8.40.097 Potassium chloride, 62%K 2 O120.11.936 Potassium sulfate, 50%K 2 O, 18%S 42.60.852 Potassium thiosulfate, 25%K 2 O, 17%S 68.02.720 1 One unit equals 20 lb 2 Salt index per 100 lbs of H 3 PO 4
Post-planting Fertilization Ability to do this is limited by crop characteristics and equipment. Fertigation is the best way to do this, but is only possible in irrigated systems Should be guided by ________________. tissue tests
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