Chapter 8 Soil Fertility and Nutrient Bioavailability
Soil Fertility and Nutrient Bioavailability Chapter 8
Soil fertility Soil fertility is the characteristics of soil that enables it to Provide nutrients in adequate amounts in adequate time in appropriate balance for growth of particular plant(s)
Soil Fertility Soil fertility is the characteristics of soil that enables it to: • Provide nutrients • in adequate amounts • in adequate time • in appropriate balance • for growth of particular plant(s)
Soil Fertility Depends on the Forms of the nutrient in soil Processes of nutrient release to soil solution(weathering, decay, dissolving and desorption) Movement of nutrients to the absorbing surfaces(of plant/mycorrhiza) Mechanism of absorption by roots
◼ Depends on the: ◼ Forms of the nutrient in soil ◼ Processes of nutrient release to soil solution (weathering, decay, dissolving, and desorption) ◼ Movement of nutrients to the absorbing surfaces (of plant/mycorrhiza) ◼ Mechanism of absorption by roots Soil Fertility
Topics Cycling of different elements Soil processes and the supply of nutrients relative importance of organic and inorganic pools/biological activity effects of pH on nutrient availability effects of soil moisture on nutrient availability and movement Movement of nutrients in soil to roots Importance of soil structure in soil fertility Bioavailability of soil nutrients
Topics • Cycling of different elements • Soil processes and the supply of nutrients – relative importance of organic and inorganic pools/biological activity – effects of pH on nutrient availability – effects of soil moisture on nutrient availability and movement • Movement of nutrients in soil to roots • Importance of soil structure in soil fertility • Bioavailability of soil nutrients
Plants absorb nutrients from the soil solution Concentrations in soil solution(uM) at sites in UK Na K Mg Ca Fe P Grassland/ arable4653901352120|3432764 (24 soils Woodland 33538410459224139817 (5 soils values for P can be much lower than those quoted 10 um from Tinker and nye, 2000
Plants absorb nutrients from the soil solution Concentrations in soil solution (µM) at sites in UK Na K Mg Ca Fe S P Grassland/arable (24 soils) 465 390 135 2120 3.4 327 64 Woodland (5 soils) 335 384 104 592 24.1 398 17 from Tinker and Nye, 2000 values for P can be much lower than those quoted < 10 µm
Major nutrient pools and pathways of nutrient transfers crop atmosphere stable labile InorganIc ordanIc plants microbes labile soil stable InorganIc solution organIc leaching erosion
Major nutrient pools and pathways of nutrient transfers soil solution stable inorganic labile inorganic microbes plants stable organic labile organic leaching erosion crop atmosphere
The importance of different pools and transfers varies between nutrients Relative importance of global pools Significance of inorganic and organic pools and biological cycling Solubility of inorganic forms of nutrients Buffering capaci Movement of nutrients in soil solution Replenishment of nutrients in soil solution Concentrations of nutrients in solution close to roots
The importance of different pools and transfers varies between nutrients • Relative importance of global pools • Significance of inorganic and organic pools and biological cycling • Solubility of inorganic forms of nutrients • Buffering capacity • Movement of nutrients in soil solution • Replenishment of nutrients in soil solution • Concentrations of nutrients in solution close to roots
Importance of pools varies with nutrients Nitrogen (N) Almost entirely in organic form in soil(500- 5000kg/ha); exchange NH4 0-400kg/ha Soil solution: anion and cation(NO30.1 5mM) and NHa, 0.01-0. 5mM); very soluble low buffering capacity Large inorganic pool in atmosphere(N2);very inert(unreactive
Importance of pools varies with nutrients Nitrogen (N) – Almost entirely in organic form in soil(500- 5000kg/ha); exchange NH4 + 0-400kg/ha – Soil solution: anion and cation (NO3 - ,0.1- 5mM) and NH4 + , 0.01-0.5mM); very soluble; low buffering capacity – Large inorganic pool in atmosphere (N2); very inert (unreactive)
Importance of pools varies with nutrients Potassium(K) Inorganic pools in soil and plants Crystal-lattice K, 10-10,000kg/ha Soil solution: cation(K+),0.05-2mM; soluble EXchange K+, 10-500kg/ha Atmospheric pool negligible
◼ Potassium (K) ◼ Inorganic pools in soil and plants ◼ Crystal-lattice K, 10-10,000kg/ha ◼ Soil solution: cation (K+), 0.05-2mM; soluble ◼ Exchange K+, 10-500kg/ha ◼ Atmospheric pool negligible Importance of pools varies with nutrients
Importance of pools varies with nutrients Phosphorus (P) Both inorganic and organic pools in soil Organic P: 5-100kg P/ha Absorbed soil phosphate(inorganic P): 20 500kg soil solution: anions(H2PO4/HPO42-, depends on pH): 0. 1-2uM High buffering capacity
◼ Phosphorus (P) ◼ Both inorganic and organic pools in soil ◼ Organic P: 5-100kg P/ha ◼ Absorbed soil phosphate (inorganic P): 20- 500kg ◼ soil solution: anions (H2PO4 - /HPO4 2- ,depends on pH); 0.1-2μM ◼ High buffering capacity Importance of pools varies with nutrients