Singh - 2018 - Are N Fertilizers Deleterious to Soil Health?
Singh - 2018 - Are N Fertilizers Deleterious to Soil Health?
Abstract: Soil is one of the most important natural resources and medium for plant growth. Anthropogenic interventions such as tillage, irrigation, and fertilizer application can affect the health of the soil. Use of fertilizer nitrogen (N) for crop production influences soil health primarily through changes in organic matter content, microbial life, and acidity in the soil. Soil organic matter (SOM) constitutes the storehouse of soil N. Studies with 15N-labelled fertilizers show that in a cropping season, plants take more N from the soil than from the fertilizer. A large number of long-term field experiments prove that optimum fertilizer N application to crops neither resulted in loss of organic matter nor adversely affected microbial activity in the soil. Fertilizer N, when applied at or below the level at which maximum yields are achieved, resulted in the build-up of SOM and microbial biomass by promoting plant growth and increasing the amount of litter and root biomass added to soil. Only when fertilizer N was applied at rates more than the optimum, increased residual inorganic N accelerated the loss of SOM through its mineralization. Soil microbial life was also adversely affected at very high fertilizers rates. Optimum fertilizer use on agricultural crops reduces soil erosion but repeated application of high fertilizer N doses may lead to soil acidity, a negative soil health trait. Site-specific management strategies based on principles of synchronization of N demand by crops with N supply from all sources including soil and fertilizer could ensure high yields, along with maintenance of soil health. Balanced application of different nutrients and integrated nutrient management based on organic manures and mineral fertilizers also contributed to soil health maintenance and improvement. Thus, fertilizer N, when applied as per the need of the field crops in a balanced proportion with other nutrients and along with organic manures, if available with the farmer, maintains or improves soil health rather than being deleterious.
That was a good read. The associated loss of C from mineralization due to over supplying N is something I've come across in other studies but I didn't expect additional SOC storage as a result of a carefully under-supplied N fertilizer. A comparison study on some of the commonly used fertilizer salts and their effect on soil carbon using these tests would be neat.
Thanks very much for taking the time to read an article from my cache!
There's a lot of (poor word choice pending...) 'hype' around fertilizer salts and their potential impact on the microbial and fungal communities. However, I tend to consider these as smaller part of a larger problem. The acidification effect of N fertilzer use is also nothing to sneeze at and can creep up fast on land mangers.
In my opinion, tillage is really what's fucking our soils. It decimates the communities that establish and completely alters the oxygenation status of the soil. You get this big boom in mineralization (and a priming effect; Whoo! famers likey!) but it comes at the cost of your SOM/SOC pool. Repeated tillage results in B horizon erosion, as more and more of the subsoil is eventually pulled (admixed) into the topsoil, diluting what organic matter you have, and incorporating less desirable soil parameters (pH, texture). Eventually you get through the B and into the C, which can be even worse in quality.
Don't get me wrong; salts suck, but they're somewhat easy to deal with (gypsum, leaching).
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I think a longitudinal study about which fertilizer salts have the greatest positive correlations with increased SOC/SOM would be a boon for large scale operations since it could be a way towards a reduction of inputs all around without losing that plant growth.
I'm right there with you about tillage (This is me) though I think that many folks get up in arms about someone doing an initial till with plans for no till / no dig rather than focusing on repeated tillage as the far worse culprit. It's not just disrupting those subsoil communities, it's also oxidizing lots of the stored OM and minerals. This worsens the mixture of less desirable horizons even further, requiring even more chemical intervention. But it's gotta be mixed back in, and so on and so on.
I'm just going to press 1 until I get a person so I can subscribe