Today I had the opportunity to test some home-made compost made from chicken and rabbit manure, sawdust, feathers and rabbit carcasses, together with plant matter deriving from papyrus plant and other pruned vegetation. Tap water was only applied once at the beginning.
I was quite surprised with the high level of Na and Cl ions present in the tested sample. This led me to ask myself if compost can cause any damage to soil and how can a farmer/gardener get rid of such ions when present in soil. Are there any plants which are capable to extract such ions from soil? and if so, what will happen if vegetative matter deriving from such plants is used to produce compost?
It is to be said that in my country, we experience rainfall only from November until February/March. Tap water is made out of a 50:50 mixture between de-salinized water and ground water. The latter's quality is unknown as the majority is said to be a bit saline as a result to over-extraction throughout the years. Moreover, tap water is treated with chlorine.
Cl is not harmful to plant. Actually its a nutrient. However Na can be harmful due salinity. If there is a good supply of water and the compost application rate is not so high, you should have no problem with Na. Anyways you can monitor salinity by accessing the soil eletric conductivity or Na saturation. If the levels os Na were high, you can use calcium sulfate and irrigation (water washes sodium away).
Simple flushing of soil or at the most , leaching with non-saline water would do the work..
Sodium is replaced by more favorable calcium ions. You may use calcium based amendment or calcium carbonate present in the soil whose solubility may be enhanced by application of organic amendments or acid formers. The amount and type of chemical amendments required to reclaim depend upon pH, EC and ESP of the soil/material.Crop tolerance to sodicity and economic condition of the farmers determine the desired level of replacement of exchangeable sodium. You may use Gypsum or phospho-gypsum. I also agree with Dr. Lucas that Cl may not be harmful at your concentration. You may also go for flushing as suggested by Dr. Srivastava.
For determining if the sodium and/or chloride being a problem from compost you need to also look at the nutrients. Its the ratio of nutrients vs Na and Cl thats important. Called the AgIndex. Calculate as follows: (N + P2O5 + K2O) / (Na + Cl) = AgIndex. Below 2 and you can have a Na and/or Cl build up in the soil. Above 10 and no chance of Na or Cl being a problem because if the application is that high the excessive nutrients would have killed the plants before the Na and Cl had the chance. Between 2 and 10 you want to look at both receiving soil and compost to determine application rate. Any compost above 4 will likely be no problem from specific ions. Add too much and all salts together will be the problem.
Hi Kurt,
Na and Cl could be constituents of all the components of the compost, including as you hinted, the tap water used to wet the mixture. The easy tests to do are electrical conductivity and pH. As already stated, on a small scale leaching with good quality water will remove much of the salt but make sure the leachate does not cause problems. With that climate leaching is a job for the wet season..
The next most important property of compost is C:N, because values exceeding about 12:1 indicate that when applied to soil, ongoing microbial activity may deplete the soil of available N.
Yes, Na is required in only small amounts by plants; however, depending on the species, excess of either Na or chloride, or both, can be toxic. Read the excellent text on mineral nutrition by Marschner.
Regards, Paul.
The salinity you indicated in the compost might be from the material used for composting / if the ground water used for composting contains Na and Ci at higher level. If the compost is used for soil application there may be chance for build up of salinity in the soil. before the application of compost of in large scale you can do experiment in small plots by applying compost and growing of plants and test the soil for salinity. the salinity build up also vary with soil type. but the chloride salt can be leached down by applying good quality water or rain water.
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