Mineralizable N In the Kentucky NRCS Soil Bank Study.

From 2009 through 2011 soil samples were collected across Kentucky by producers participating in individual environmental grants sponsored by the Kentucky Division of Conservation and designed by the USDA-NRCS.  As part of those grants, cropping systems were designed to maintain and improve the soil’s physical, biological, and chemical properties and to maximize the natural benefits received from them.  Base components of all designed cropping systems were: no-tillage, organic matter on and in the soil surface (plant residues on soil surface/roots in the soil surface), applications of light amounts of animal waste or compost, and maximum plant diversity (cover crop mixtures and crop rotations).  Project goals were to maximize soil health through increased additions of soil C, increased soil pore space, re-establishment of a healthy broad diverse soil microbial food web, and increased soil cation exchange capacity.  One measurement used to determine the success of that effort may be incremental increases in available soil N.  We analyzed samples over a three-year period for rapidly mineralizable soil N, by anaerobic incubation, and for total mineralizable N in 2011 by long-term aerobic incubation. Considering only those cropping systems sampled each year, % total N and % total C increased 26 and 28%, respectively between 2009 and 2011. Rapidly mineralizable N increased over 200% for the same period, and this was apparent by the second year of the study. There was a good linear relationship between rapidly mineralizable N and total mineralizable N measured after a two-week interval in 2011. No good relationships existed between rapidly mineralizable N and basic soil nutrients such as P,K,Ca, and Mg. The relationship between mineralizable N and either total N or total C was best fit to a polynomial function. Overall, the practices employed in this study appear to be successfully increasing available soil N with time.