Title: Phosphorus Nutrition and Fertility Speaker: Bill Pan online.wsu.edu
life death soil fertility From Bones, Rocks to DNA
Macronutrient Next to nitrogen, phosphorus is the second most commonly limiting nutrient in crop production. This may be the essential nutrient we run out of first! Although it exists in nature in the anion form, don t be fooled! It doesn t behave at all like nitrate.
Typical plant tissue conc.: 0.1% to 0.4%, or about 1/10 of N, K conc. Absorbed by plants primarily as monovalent anion (H 2 PO 4- ) Biochemical functions structural component of phospholipids, nucleic acids high energy bonding in ATP, others
IPNI, 2008
Bergmann, 1992
P Deficient Merlot Grape Wolf, 2004
Lock et al., 2002
http://www.gardenscure.com/420/latest-growfaq-entries/89618-plant-abuse-chart-photosnietzsche.html
OH OH O O HO P=O O P=O O P=O O P=O OH OH OH O More Acid H 3 PO 4 H 2 PO 4 - HPO 4 2- PO 4 3- Absorbed by plants
Organic Phosphorus inositol phosphates nucleic acids phospholipids phosphosugars Inorganic Phosphorus adsorbed P primary, secondary minerals
P adsorption: attachment of soluble P anion to soil surface. P precipitation: formation of insoluble compound from two soluble ions. P fixation: any chemical change that reduces the amount of P that plant roots adsorb.
PHOSPHATE RETENTION BIOLOGICAL CHEMICAL In all soils during decay of organic residues low in P Adsorption by Fe-Al oxides and Clay minerals Precipitation Greatest in acid Soils Insoluble Fe-Al Phosphates Ca-phosphates Insoluble carbonated hydroxyapatite Acid soils Near acid to neutral soils Calcareous and some alkaline soils
Ca 2+ + H 2 PO 4 - +2H 2 O =CaHPO 4. 2H 2 O +H + soluble ions precipitate on soil surfaces Soil Solution Soil Colloid alkaline conditions drives this reaction by consuming H+, one of the reaction products
soluble soluble precipitate ion ion on soil surfaces Soil Solution Soil Colloid What ph conditions encourage the shifting of this reaction towards dissolution?? Why??
Potash and phosphate institute
Al OH H+ O Al OH H+ O soil colloid HO OH P=O O
O Al OH H+ HO Al O P=O OH O OH H
O Al HO OH H Al O P=O OH O OH H
O Al Al O O P=O OH OH H strongly adsorbed, O OH H difficult to displace; similar reaction for Fe oxides
Amount of P fixation in soil tend to be older, highly weathered soils in humid climates. tend to be newer, temperate soils very high Highest P availability high medium low Fefixaton Alfixation Cafixation 3 4 5 6 7 8 9 Soil ph {
Available Phosphorus Recall that P reacts with various inorganic and organic soil components. Relative importance of different P reactions varies by regional soil characteristics. Therefore, different soil tests have been developed for different soils.
Phosphorus Soil Tests in WA Eastern WA, ph<7: NaOAc test; Morgan test, 0-6 ppm P is considered deficient. Central WA, ph>7: NaHCO 3, Olsen test, 0-12 to 18 ppm P considered deficient. Western WA, ph<<7: HCl + NH 4 F, Bray test, 0 to 10 ppm P deficient.
Mycorrhiza = "fungus root"
Ectomycorrhizae: mainly on trees. Rootlet is bounded by layer of fungal material known as the sheath or mantle.
Endomycorrhizae: Vesiculararbuscular (VA) mycorrhizae Vesicles: 10-100um expansions of hyphae between or sometimes within cells, store lipids. Arbuscules: highly branched hyphae within cortex cells. Site of nutrient transfer. Fungus penetrates cortical cells, no mantle formation. Network of fungal mycelia fans out into soil. Most important group, distributed worldwide. nearly all cultivated plants, most herbacous plants, many trees. very old association: Oldest fossils of terrestrial plants show fungal structures similar to VAM.
Content in Shoots (ug) No P fertilizer 25 ppm P added Element No Myco Mycorrhiza No Myco Mycorrhiza P 750 1,340 2,970 5,910 K 6,000 9,700 17,500 19,900 Ca 1,200 1,600 2,700 3,500 Mg 430 630 990 1,750 Zn 28 95 48 169
Mycorrhizal associations most common in areas of low P availability. In several cases they have been shown to be important or even essential for plant performance. However, there can be circumstances in which the fungus is mildly detrimental, and others in which the plant feeds from the fungus.
1. Rarely nutrient-stressed roots do not attract or allow colonization 2. Less photosynthate goes to roots less food signal for symbiont.