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Does green manure need to be reinnocculated?


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Was happy with the results from planting a couple of kilos of green manure (sun bean). Will the second generation beans collected from those plants already have the microorganisms that help the soil or do I need to add inoculant for good results?

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If you inoculated the initial planting, and are seeding the same plot relatively soon after incorporating the original, there is a good chance that the soil will contain adequate rhizobia for re-inoculation, if all factors for healthy soil life are maintained (like adequate and balanced mineral nutrients and water management), and no harsh chemistry applied. 

 

From my understanding (those with more experience or science, correct me if I'm wrong): Don't count on the gathered seed carrying the inoculant, but rather the soil, so if seeding additional areas or if in doubt: 

 

"Inoculate seed with cowpea-type (EL) rhizobia and drill seed at 30 to 50 lb/acre (USDA-NRCS, 2009) 1 inch deep on 6-inch rows in a tilled, weed-free seedbed. A higher seeding rate of 49–58 lb/acre has been used to establish thick stands for green manure (Wang and McSorley, 2009) and higher rates are also used in fiber production to insure upright stems, produce finer fiber, and to increase yield (Duke, 1983)."

https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/njpmcpg11706.pdf

 

https://davesgarden.com/guides/articles/view/2429/

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On 11/14/2020 at 1:14 PM, islandguy said:

Was happy with the results from planting a couple of kilos of green manure (sun bean). Will the second generation beans collected from those plants already have the microorganisms that help the soil or do I need to add inoculant for good results?

 

I presume you are talking about Sunn hemp (Crotalaria juncea).  Sunn hemp will noculate freely with the native cowpea rhizobium bacteria in the soil. I also presume you are planting it in Thailand. Sunn hemp is widely grown in many regions in Thailand, particularly in the north and northeast. I far as I know, none of the farmers innoculate their seeds. The rhizobium is in the soil and not in the seeds. You may very well indeed get better growth with added rhizobium, but as the crop is only a green manure it wouldn't be worth your trouble. A lot of sunn hemp seed in Thailand is given away free by various government departments or at a very cheap price (20-25 baht/kg). This seed is normally not very clean and has a high contamination of weed seeds. Be careful and select only pure sunn hemp seed with no weed seeds. 

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Thank you for the information, Michael. What is your opinion on whether to cut the Sunn Hemp early when it is not fibrous or whether to let it fully mature? Would only cost me about 700 baht to get it tilled by a tractor, cutting early is no extra cost. Won’t be replanting that area before June. Also, if the seed is not inoculated does it actually have an effect on the amount of rhizobium in the soil after it has been planted? I thought the extra nitrogen from the rhizobium  was why you planted it?  

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The nitrogen comes from the nodules formed on the roots by the rhizobium bacteria. Gently pull up a few plants and examine the roots. There is no need to wait until Sunn hemp flowers before cutting and cultivating it into the soil. Soft, leafy green matter will work into the soil better than stemmy fibrous matter. You can also cut high and let the plants regrow from the stems for a second cut which is the final cut that you cultivate into the soil. Remember than you are wanting green manure which is high in nitrogen to be worked into the soil. The roots fixing soil nitrogen is just one part of the nitrogen supply. 

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