The Effects of Fertilization on Soil Ecology

1. The Effects of Fertilization on Soil Ecology Adapted from a presentation by : Craig Cootsona Kim Littke

2. Lecture topics • Background • Effects of fertilizers on: • Physical and Chemical environment • Soil Microbes and Soil Fauna • Decomposition • Mycorrhizas • Specific Fertilizer effects • N, P, Liming, and Wood Ash

3. High yields achieved in crop production in the United States require that large amounts of nutrients be applied to the soil to replace those withdrawn during the production cycle. • Animal manure and other organic materialscontribute to nutrient replacement, • But commercial fertilizers remain the major source of applied plant nutrients. • (Economic Research Service (ERS) – USDA) 3

4. and Forest fertilizer use is small comparedto agriculture 4

5. Forest fertilization - nutrients • The two nutrients most commonly used in forest fertilization applications are P and N. • P is the primary nutrient used at the time of establishment and in the early stages of stand development. 30-50 pounds of elemental P per acre. • N is more concentrated in mid-rotation applications, often following thinning. 100-300 pounds of N per acre. • Common fertilizer formulations used include: • Diammonium Phosphate (DAP: 18-46-0), • Triple Super Phosphate (TSP: 0-46-0), • Ammonium Nitrate (34-0-0), and • Urea (46-0-0). 5

6. Forest fertilization – SE USA • Forest fertilization has been used fairly extensively for decades in the management of slash pine on P deficient sites in the lower coastal plain. In 1996, it was estimated that industrial forest companies fertilized around 600,000 acres in the Southeast U.S. The most dramatic increase in treated acres occurred with mid-rotation fertilization, often following thinning. 6

7. Forest fertilization – PNW USA • Most PNW Douglas-fir forest sites are N deficient. Mineral cycling research has shown high C/N ratios and low nitrification rates for soils in the region. • In western OR and WA urea is applied to Douglas-fir stands over a range of soil and forest stand types. About 100,000 to 120,000 acres are fertilized each year. Most current management plans call for fertilization in multiple applications. But there has been a drop of in applications in recent years. • Operational fertilization of other species is minor. 7

8. Fertilizer effects on soil properties • Mostly it influences the soil chemistry - increase nutrient levels in forest floor and soil. - strong influence on pH (but depends on fertilizer)

9. N-Fertilization Effects on Soil • Nitrogen fertilization is more common on poor to medium quality sites in the Northwest (Fox, 2004) • Common types: urea (CO(NH2)2), ammoniumsulfate, ammonium nitrate, potassium nitrate. • Fertilization with urea initially increasespH, but decreases soil pH over time because of nitrification • But, excessive nitrogen inputs can leachexchangeable cations from the soil • More is not necessarily better 9

10. Fungi and decomposition Fertilization increases nutrient content of organic matter and therefore helps Sustains high microbial populations Increases decomposition rates (Miller et al., 1989 and Muller, 1988) 10

11. N-Fertilization and Microbial Activity • Some studies show N-fertilization reduced microbial activity and biomass (growth rates decreased and recalcitrant material increased) (Arnebrant et al., 1996 and Lee and Jose, 2003) • Greatest positive effect was seen on low fertility sites • Adding more N to a fertile soil makes less of a difference • Suggests importance of initial site health http://www.naturalhistorymag.com/scienceresources/images/microbes.jpg Stuffed Microbes 11

12. N-Fertilization and Decomposers • Differential effect on litter decomposition • Typically stimulates cellulose degradation (Fog, 1988) • But N differentially affectsphenol oxidase production • Released by microbes to decompose lignin • Initial lignin concentration makes a difference (Carreiro et al, 2000) • Low Lignin: Flowering Dogwood • N addition caused increased decomp by 50% • High Lignin: Oak • N addition caused decreased decomp by 25% by inhibiting ligninolytic enzyme production http://www.pilzfotopage.de/Aphyllos/images/Fomitopsis%20pinicola.jpg 12

13. Mycorrhizas • In low nutrient areas, plants generally investmore carbon in mycorrhizal fungi (Mosse & Phillips, 1971) • But if nutrient availability rises (eg, fertilization), plants allocate carbohydrates elsewhere in the plant • And a decline in mycorrhizal abundance is expected with fertilization as the mycorrhizal fungi become C-limited (Read, 1991) • On the other hand, it is possible that mycorrhizal fungi are directly limited by soil nutrient availability and should proliferate following additions of N or P (Tresender and Allen, 2002) 13

14. N-Fertilization and Mycorrhizas • Mycorrhizal numbers • Most mycorrhizas decreased under N fertilization (Treseder, 2004) • Also, decreased ECM mycelial mat growth (Nilsson and Wallander, 2003) • Mycorrhizal colonization • Decreased under high N treatments for one species of Piloderma, • But another species was unaffected(Mahmood, 2003) • Species specific response? • Overall negative response • Supports dependence on C from plants http://www.microbe.org/espanol/art/mycorrhizas.gif 14

15. Soil Fauna • Soil Fauna can be sensitive indicators for • the nutrient (nitrogen) levels and • decomposition in forests (Jandl et al., 2003) • For example, nematodes are sensitive indicators of • physical disturbance and • altered nutrient inputs (Forge and Simard, 2001) 15

16. N-Fertilization and Nematodes • N fertilization reducednematode abundance, esp root-feeding nematodes (Forge and Simard, 2001) • Diversity was also affected • Omnivorous and root-feeding nematodes decreased • Increased nematodes that prey upon bacteria and fungi • Probably reflects increased bacterial populations after fertilization http://www.ars-grin.gov/ars/SoAtlantic/fp/stpp/burelle/nematode.html 16

17. P-Fertilization and Mycorrhizas • Mycorrhizal abundance decreased more under phosphorus fertilization than under nitrogen fertilization (32% and 15%, respectively) (Tresender, 2004) • This suggests that mycorrhizas are helping with phosphorus uptake more than nitrogen uptake http://www.torontobonsai.org/Journal/Journal.2002/mar.2002/images/ 17

18. Liming and Decomposers • Liming increases Ca levels in the soil • Slow availability of Ca after application (slow release) • Increases soil pH • Decomposition was greatest under moderate liming (6 t/ha) (Geissen and Brummer, 1999) 18

19. Liming and Nematodes • Bacterivorous and fungivorous nematodes increased in abundance after liming (de Goede and Dekker, 1993) • Have low colonizer-persistor (cp) value • Short generation time • Many offspring • Relatively tolerant to ecological disturbance (Neher, 2001) • These results are similar to some N fertilization studies Acrobeles complexus: feeds on bacteria 19 http://www.icapb.ed.ac.uk/images/wormpic.jpg

20. Wood Ash Effects on Soil • Derived from industrial applications • Boilers, Furnaces • Useful properties • ½ the liming value of limestone • Increases pH • Nutrients: 10-20% CaCO3 and 1-4% K • Returns some OM back to sites • Inexpensive http://www.woodash.net/ 20

21. Wood ash and Mycorrhizas • Wood ash amendments increased root colonization of one species of Piloderma, but decreased colonization in another species(Mahmood, 2003) • The decrease in colonization is probably due to the sensitivity of that species to pH and nitrogen levels • The favorable species also colonized ash patches with dense, mat-like mycelium (Mahmood, et al. 2001) http://www.dow.wau.nl/soil_quality/nieuw/research/mttsfdo2.jpg 21

22. Wood Ash and Mesofauna • Increase in pH from ash decreases total abundance of mesofauna • Collembola and mites (Huhta, et al., 1986 and Haimi, et al., 2000) • Experiments with smaller changes in pH show no significant change in total abundance (Liiri et al., 2002) • Suggests that mesofauna may be sensitive to larger changes in pH • Over-use of wood ash may indirectly decrease decomposition by arthropods www.ksu.edu/biology/pob/arthropods.html 22

23. Conclusions N-Fertilization • Nitrogen fertilization tends to decrease soil organism abundance - some species are unaffected • May increase or decreasepH • Decomposition may increase or decrease • High soil nitrogen levels may reduce mycorrhizas. • May increasenitrification and leaching • May increasedenitrification in wet soils 23

24. Conclusions Liming • Liming stimulates decomposers and the predators that feed on them Wood Ash • Wood ash increasesabundance of soil organisms • But those organisms that are sensitive to pH changes, may be negatively affected 24