4/17/2014. Using Compost to Improve Post-fire Water Quality. David Crohn University of California, Riverside. Acknowledgements

Transcription

1 Using Compost to Improve Post-fire Water Quality David Crohn University of California, Riverside Acknowledgements 1

2 Salts Salts are a huge concern in semi-arid and arid soils Salts accumulate from irrigation water Salts concentrate due to evapotranspiration (ET) Not a concern where precipitation significantly exceeds evapotranspiration Salts Mostly Na +, K +, Ca 2+, Mg 2+ and Cl - Decrease yields by upsetting osmotic balance in the roots zone If sodium dominates, soil structure is lost so that water and air cannot penetrate Not a concern where precipitation significantly exceeds evapotranspiration 2

3 Salt measurement Salts in water improve it ability to transmit electricity Salinity is measured indirectly Water is added and extracted from soils Its electrical conductivity is then measured < 4 ds/m is desirable, but it depends on the plant How much water is added affects results EC 2 EC 5 EC e The question Do compost salts act like other salts, depressing growth? fertilizers, stimulating growth? 3

4 Threshold soil salinity values for crops (Hanson et al., 1993; Soltanpour and Follett, 1995) Threshold EC e (ds/m) Crop 10% Yield Reduction 25%Yield Reduction Lettuce Tomato Blueberry soils Soil Textures Sand (%) Clay (%) EC e (ds/m) ph Organic Matter (%) Sandy Loam Silt Loam Clay Loam

5 9 commercial compost blends Treatment Constituents T1 steer manure and wood fines T2 steer manure and wood fines T3 wood fines, biosolids, and digested steer manure. T4 chicken manure and wood fines. T5 steer manure and wood fines T6 wood fines, biosolids, and digested steer manure. T7 wood fines and digested steer manure. T8 rice hulls, biosolids, wood fines, chicken manure. T9 ground wood fines, peat moss, worm castings, fir bark Compost properties Compost Treatment Organic Matter (%) Moisture (%) EC 5:1 (ds/m) ph 5:1 T T T T T T T T T

6 Experiment 3 soils 9 composts 3 crops replicates (324 all together) were grown in 1 gal pots within a greenhouse Control soils were fertilized Plants were collected 45 days after emergence Dry masses were measured Salts and compost Growers in California and similar environments worry about salts in compost. Compost numbers are often high 4 6 ds/m for greenwaste compost Manure, biosolids composts MUCH higher (10, 15, higher) BUT nutrients are salts!!! And much of the salinity measured is due to these nutrients Also some compost salts are organic and will decompose Compost salts are diluted in soils 6

7 Effect of different composts on dry matter yield of Lettuce at two salinity levels 6 5 ECe = 2.1 ds/m ECe =3.2 ds/m Shoot Dry Weight (g) Control T 1 T2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 Treatments Effect of different composts on dry matter yield of Tomato at two salinity levels ECe = 3.5 ds/m ECe = 5.0 ds/m Shoot Dry Weight (g) Control T 1 T2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 Treatments 7

8 Effect of different composts on dry matter yield of Blueberry at two salinity levels 10 8 ECe = 3.0 ds/m ECe = 5.0 ds/m Shoot Dry Weight (g) Control T 1 T2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 Treatments Compost nutrients, salts, and AgIndex Treatment NH 4 -N NO 3- -N P K Ca Mg S Na Cl AgIndex T T T T T T T T T Soil

9 Observations: In all cases we saw reduced growth as soil-compost mix EC e values increased from 10 to 25% salt damage levels (p<0.0001) In all cases compost use improved growth above the fertilized controls (p<0.0001) Could not predict growth 10 to 25% damage level differences from measured compost nutrients or salts using regression AgIndex was significant (p<0.05) suggesting that this ratio is meaningful Predicting the ECe of compost amended soils Soil salinity is measured using EC e Compost salinity is measured using EC 5 These are NOT comparable because the amount of water in saturated paste varies from soil to soil EC 5 > Ec e Also adding compost changes the amount of water in the saturated paste of the soil compost mix Have developed a method, based on published regression data, to predict this. 9

10 4/17/2014 Predicting the ECe of compost amended soils Here is an Excel tool that can help. Conclusions Compost salts ARE like other salts. Too much can be harmful The benefits of using compost far outweigh the risks however The AgIndex can be used to guide compost choices where salinity is a concern The ECe of compost-soil mixes can be predicted from soil and compost (TMECC) measures 10