Assessing manure and inorganic nitrogen fertilization impacts on soil health, crop productivity, and crop quality in a continuous maize agroecosystem

Authors: MINER, GRACE - Colorado State University; Delgado, Jorge; IPPOLITO, JAMES - Colorado State University; Stewart, Catherine; Manter, Daniel; Del Grosso, Stephen - Steve; Floyd, Bradley; D Adamo, Robert

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2019
Publication Date: 6/12/2020
Citation: Miner, G.L., Delgado, J.A., Ippolito, J.A., Stewart, C.E., Manter, D.K., Del Grosso, S.J., Floyd, B.A., D Adamo, R.E. 2020. Assessing manure and inorganic nitrogen fertilization impacts on soil health, crop productivity, and crop quality in a continuous maize agroecosystem. Journal of Soil and Water Conservation. 75(4):481-498. https://doi.org/10.2489/jswc.2020.00148.
DOI: https://doi.org/10.2489/jswc.2020.00148

Interpretive Summary: Sustainable agricultural production requires an inclusive framework that considers not only crop productivity (i.e., yields), but also considers the impacts of farming methods on soil health and crop nutritional quality (i.e., mineral nutrient density). However, the impacts of different nutrient management methods on soil health, crop yields, and crop quality are not well understood. We evaluated these linkages in a continuous corn experiment with treatments varying in nitrogen (N) fertilizer amount and type (zero input control, inorganic N, and manure-based organic N). We assessed soil health indicators, crop yields, and crop nutrient concentrations after six cropping years, and utilized a tool called the Soil Management Assessment Framework (SMAF) to assess soil health. We found that soil health as well as crop yields were greater in the inorganic and organic N treatments than in the control, supporting the linkages between healthy soils and crop productivity. While the overall soil health index calculated by the SMAF tool did not differ between the two N sources, there were additional nutrient benefits of manure that the tool did not adequately capture. Crop nutritional quality differed between treatments. Grain [N] was 40% greater in the inorganic and manure N treatments than in the control. Grain [P], [K], and [Mg], important elements in livestock nutrition, were 10 - 28% greater in the manure treatment than in the inorganic N treatment. Additionally, although a yield dilution of grain [Zn] occurred in the inorganic N treatment, the dilution effect was mitigated with manure, likely due to increases in soil Zn. Overarchingly, we found that both inorganic and organic N amendments increased soil health and crop productivity over the unamended control, and that the manure N treatment increased crop nutritional quality above the control and inorganic N treatments.

Technical Abstract: Sustainable agricultural production requires a more inclusive framework that considers the impacts of production methods on soil health and crop nutritional quality in addition to crop productivity. However, few studies have directly examined the potential associations between management impacts on soil health (SH), crop productivity, and crop quality. We evaluated these linkages in a continuous maize experiment with treatments (trts) varying in nitrogen (N) fertilizer amount and type (zero input control, inorganic N, and manure-based N trt). We assessed select SH indicators after six cropping years, and computed SH indices using the Soil Management Assessment Framework (SMAF). Crop yields, mineral nutrient concentrations [ ] and nutrient uptake were analyzed in years five and six. Manure application increased biological SH indicators compared to control and inorganic N trts and increased available potassium (K), zinc (Zn), copper (Cu), and phosphorus (P). Additive SH indices were higher in the inorganic N and manure trts than in the control but did not differ between the two N sources, despite the large exogenous sources of C, N, and nutrients applied via manure. The SMAF tool only directly considers P and K in terms of soil nutrients — other nutrient benefits of manure application (i.e., increases in total soil N, available Cu and Zn) were not accounted for, suggesting that the SMAF nutrient SHI should be modified to account for the impacts of management practices on nutrient availability. Crop productivity was higher in trts with higher overall SH, supporting the linkages between SH and crop productivity. Despite widely differing nutrient inputs and soil fertility levels, we found no yield differences between the two N trts. However, there were notable trt impacts on crop quality. Grain [N] was 40% greater in the urea and manure trts than in the control. Grain [P], [K], and [Mg], important elements in livestock nutrition, were 10 - 28% greater in the manure trt than in the urea trt. Additionally, although a yield dilution of grain [Zn] occurred in the urea trt, the dilution effect was mitigated in the manure trt, likely due to do increases in available Zn. These results suggest that improvements in SH can be correlated not only with improved productivity, but also with improved crop nutritional quality, which could have cascading positive benefits on animal and human health.