Book Description

The planet's arable soils are rapidly degrading, primarily through mismanagement, erosion, and pollution. In contrast, some of the most fertile soils in the world lie under grasslands, such as in the Central Plains region of the United States. These soils were developed over thousands of years through wind depositions and through the deep roots of native grasses and forbs, each year depositing the organic matter and carbon of old roots under the surface. The eastern edge of US grasslands is occupied by Tallgrass Prairie, 98% of which has been converted to row crops and human use. There remains, among these soils, small remnants which have remained uncultivated or plowed, and which are likely the best remaining examples of grassland soils from before modern agriculture. To improve and preserve the agricultural soils throughout the Midwest, it is essential to thoroughly understand the soil properties of these remnant soils. Currently the most widely recognized and comprehensive suite of soil tests available for analyzing chemical, physical, and biological aspects of soil is the Comprehensive Assessment of Soil Health offered by the Cornell Soil Health Laboratory (CSHL). Multiple government and research groups use this testing service for the quantification of soil health properties. The goals of this study are to use Cornell University's Comprehensive Assessment of Soil Health tools to: 1) evaluate the soil health of remnant tallgrass prairies in Nebraska, by quantifying a suite of relevant physical, chemical, and biological soil properties collected at multiple remnant sites; 2) compare the data from these remnant grasslands with comparable data collected in nearby agricultural fields to determine the degree and type of soil degradation which may have occurred there; and 3) use the profile characteristics of the remnant soils as a benchmark for evaluating soil health of samples derived from a region-wide data base for agricultural soils of collected from former prairies throughout the Great Plains. In the Nebraska Tallgrass Prairie region, nine research sites were identified. Five remnant sites were paired with one of four nearby agricultures sites that had a similar soil type, slope, and elevation. At each site, five subsamples were collected at 0-15 cm and at 15-30 cm soil depths. The samples were analyzed for soil texture, available water capacity, organic matter percentage, soil protein, soil respiration, active carbon, pH, total carbon, total nitrogen macro and micronutrients. The data analyses were conducted using R Studio, and the results of the remnant sites and of the agricultural sites were compared: 1) with each other, and 2) with selected samples from the CSHL Prairie State Database (PSD). There were significant differences between the remnant soils and the agricultural soils at 0-15 cm. Differences were most pronounced in the biological soil properties, with remnant soils exhibiting higher values among soil health properties that measure soil functional capacity. This pattern was also evident in the physical soil properties, although the differences were not as pronounced. In the chemical analyses, higher nutrient concentrations were found in the remnant sites than in the agricultural sites, apart from phosphorous, which was significantly higher in the agricultural sites. Similar patterns were found in the samples from 15-30 cm depth, although less pronounced. Pearson's Correlation revealed significant correlations among the biological indicators, particularly among carbon-related soil properties. In addition, a Principal Component Analysis identified associations among indicators strongly associated with microbial activity and organic matter quality. Comparison of the Nebraska samples with the Prairie Soils from the broader CSHL data base was especially insightful as soils from the remnant sites had higher soil health indicators for every property measured, except phosphorous, iron and zinc. In general, this study indicated serious degradation in the agricultural soils as compared with the remnants, with total nitrogen showing the highest difference, followed by various forms of carbon. The comparison of remnant prairie sites with agricultural sites in eastern Nebraska quantified what is apparently a breakdown of healthy soil functions in active agricultural land, as a result of long-term agricultural practices. The remnant soil health profiles presented here can therefore serve as a reference for guiding management and restoration of agricultural systems throughout the Tallgrass Prairie Region. This study also highlights the powerful approach of using the CSHL comprehensive soil analyses in combination with remnant grasslands as diagnostic tool for other types of grasslands across the Great Plains and globally.