Soils can also have too much salt
The researchers looked at how organic fertilizers can improve soils that have built up a significant amount of salt. This accumulation causes the soil to be saline, wherein it contains enough soluble salts to negatively affect crop growth. The Food and Agriculture Organization measures soil salinity in deciSeimens per meter (dS/m) and uses these classifications.
- Non-saline (0-2 dS/m) – Salt levels in the soil are between normal to negligible.
- Slightly saline (2-4 dS/m) – Salinity levels can cause salt-sensitive crops to have limited yields. Some examples include beans, eggplants, and strawberries.
- Moderately saline (4-8 dS/m) – Soil at these levels adversely affects the yield of many crops.
- Strongly saline (8-16 dS/m) – Only a few crops can yield under this soil, such as barley, guar, wheat, and rye.
- Very strongly saline (over 16 dS/m) – The salt levels in the soil can restrict the yield of most crops, save for sorghum, squash, and onion bulbs, in lower levels, and certain types of grains.
It's worth noting that while there are many areas in the world that have naturally saline soils, modern agricultural practices have greatly degraded soil quality, leaving soils devoid of nutrients and with excessive salt levels in their wake. This phenomenon lends itself to a vicious cycle of crops in saline soil being bombarded with synthetic fertilizers that strip away nutrients and retain salt.
For the study, the scientists looked at two things: the quality of irrigation water – one of the main factors that contribute to soil salinity – and its effects on sensitive microbes. Earlier studies show that while certain soil microbes are beneficial to crop health, these often have a low tolerance to saline soil. As salt levels increase, these not only kill sensitive microbes, but also reduce their activity, which includes converting compounds into nutrients that can be used by crops.
Organic diet is also beneficial for microbes
The team studied how organic fertilizers counteract this adverse effect. In their experiment, the team used soil samples with different salinity levels. Organic amendments -- ground biochar, rice straw, farmyard manure, and glucose -- were added to the soils, then they were incubated for eight weeks. They tested it for cumulative respiration, which indicates the presence of organisms in the soil; microbial biomass carbon, an indicator of how much carbon is inside a soil organism; and available nutrients such as nitrogen and phosphorus.
Based on the results, the researchers found that soils that had high levels of salinity had significantly lower levels of cumulative respiration and microbial biomass carbon, which indicated an inverse relationship between soil health and salinity. However, adding organic fertilizers improved soil health, despite their salt levels.
Among the organic amendments that they used, they found that soils treated with glucose had the highest levels of organisms in the soil. Glucose-amended soils had doubled their cumulative respiration levels compared to others. In terms of nitrogen and phosphorus in the soil, those that were treated with farmyard manure had higher levels than soils treated with glucose. The team noted, however, that high salinity levels can still impair the ability of microbes to properly utilize nutrients.
In sum, the researchers concluded that organic fertilizers can greatly improve soil health, regardless of its salinity.
Harvest.news has more stories about organic farming methods that improve soil health for better crop yields.
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