Excellent result. Cover crops improve soil biology obviously through the decomposition of the green biomass by bacteria and fungi. A narrow C:N ratio material stimulates bacteria more than fungi. Also the root exudates stimulate soil microbes.
Dear Sir!
You are right but what should be their impact on greenhouse gases emissions, because usually the trend is that higher microbial activity is responsible for higher methane or CO2 emission, But we got lower CO2 emission after incorporation of cover crop during rice cultivation season.
Can you specify what was the cover crop used, what as its N content, C;N ratio and what as the amount added in terms of tonnes/ha. Whether rice was grown under continuous flooding or was it intermittent flooding? Whether carbon dioxide evolution was measured in situ or was it a lab simulation study using dried cover crop biomass addition. If so rate at which added. How long was C02 evolution measured?
We cultivated barley and hairy vetch cover crops during winter dry seasons having the Korean recommended dose for seeding of 180 kg ha-1 and 90 kg ha-1 respectively. These were harvested and incorporated in to the soil one week before the rice cultivation starts. cover crops were cultivated under dry season, however after incorporation the rice was kept under flooding condition. CO2 was measured in the field under the dry upland condition and during rice cultivation under flooding.
Hi Xiaobo Li!
Yes, the cover crop incorporation in the field has increased the Fungal PLFA as compared to control.
No i have not considered the cover crop PLFA, because GC-MS of the soil sampling after cover crop incorporation only give us the total soil PLFA, we cannot say precisely that which PLFA comes from organic matter addition and which PLFA was already existed. Butin my opinion we can compare the PLFA during cover crop cultivation and during cover crop incorporation.
Your suggestion will be highly appreciated.
Dr. Israr, the important point to consider here is that: 1) when green biomass both cereal (barley) and legume (vetch) are turned over and decomposed under waterlogging conditions for rice they would be readily attacked by bacteria because C:N ratio is low. Fungi would increase only when more resistant fractions with high C:N ratio are added. 2) both the initial CO2 evolution rate as well as the cumulative amount evolved over the whole study period should increase as compared to unamended control.
Thanks Sir Desiraju RAO and Mr Xiaobo Li for your valuable suggestions
Life of soil microbes is substrate limited by nutrients and conditions which constrain their development and reproduction. . Cover crops conserve the environment by their physical coverhabitat and as food source nutrient..
They increase the available nutrient level through the exudation by root exudation and the residue that is produced . Food produced above the ground is repatriated into the ground. Secondly as the materials are decayed this stimulation of population and diversity can subside unless efforts are made to continue the regenerative process by using organic amendments and not using agrichemicals that will reduce the population and diversity of soil microbes. The soil in some sense is alive and as in all living things they need to be fed.
Hi Xiaobo Li!
Regarding the increase in fungal PLFA, we have to consider the upland dry and wet flooding condition as well. because just one week before the rice cultivation we incorporated the harvested cover crop biomass and was kept the field under continuous flooding.
According to
Mille-Lindblom C, Fischer H, Tranvik LJ. 2006. Antagonism between bacteria and fungi: substrate competition and a possible tradeoff between fungal growth and tolerance towards bacteria. Oikos 113:233–242.
soil fungi PLFA increases with increasing water availability, they may exclude soil bacteria, thus reducing the abundance bacteria
Actually here we have to keep in mind both the biotic and abiotic impacts on soil microbial community structure.
Hi Xiaobo Li!
Due to the fact that PLFAs are known to degrade rapidly in soil after cell death, it is not likely that PLFAs from the green manure material contributed significantly to the soil PLFA profile in our study, especially since sampling was not carried out immediately after amendment
Dear Muhammad Israr Khan, As XIaobo Li pointed out the effects of green manure while dramatic can be both dramatic and short lived.
To optimize the health of your rice crop consider incorporating into your system the return of hardened organic matter in the guise of mature compost.
Compared to green manure and raw manure the inclusion of mature compost gives greater effect both later in the growing system and into future seasons by more conclusive season to season Carbon sequestration.
If you can use the winter cover such as hairy vetch it can provide the total Nitrogen needs for rice. With a mulch roller and no till drill the reside can provide weed control so use of herbicide can be avoided.
Finally if you have Silicon amendment available it hardens the plant to disease pathogens and makes the Carbon in residue less prone to decomposition. A reenvisioned rice production system can eliminate the major issues related to chemical use in the crop and optimize the sequestration potential and energy efficiency while minimizing inputs and impacts.
This result was obvious, IMHO. Cover crop incorporation will stimulate the development of Saprophytic Fungi (you did have an increase of 18:2w6c, right?). Decomposition will be fairly rapid and supply bacteria with simpler carbon sources, which will also increase their numbers. The question here is (and I am curious about this): how was the Gram-positive vs Gram-negative PLFA biomarkers ratio compared with controls and did it evolve in time? Usually Gram-negative dominate over Gram-positive in undisturbed soils such as forests with a thick layer of dead leaves covering soil, while Gram-positive tend to be more important in agricultural soils (even for example with no-till technique, Gram-negative biomarkers fall in numbers compared to controls).
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