A soil quality and metabolic activity assessment after fifty-seven years of agricultural management

Authors: Stott, Diane; Karlen, Douglas; Cambardella, Cynthia; Harmel, Daren

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2013
Publication Date: 5/10/2013
Citation: Stott, D.E., Karlen, D.L., Cambardella, C.A., Harmel, R.D. 2013. A soil quality and metabolic activity assessment after fifty-seven years of agricultural management. Soil Science Society of America Journal. 77(3):903-913.

Interpretive Summary: Soil quality assessment is a proactive process for understanding the long-term effects of soil and crop management practices within agricultural watersheds. The objective of this study was to assess the impact of management on the soil quality in fields where the management history is known for close to six decades. The fields were located near Riesel, TX on the Houston Black soil series that has a high content of clay and shrink-swell properties. We sampled five sites representing an untilled remnant native prairie (NP), two previously tilled for row crops and then seeded to coastal Bermuda grass 57 (CBG) and 31 (CBTL) years ago, and two fields that have been continuously cropped for most of the last 57 years (RCTL and RC). The native prairie and Bermuda grass fields have either been grazed or had grass removed as a hay crop, depending on the year. Two fields, RCTL and CBTL, have had turkey litter applied for the last 6 yrs. Twenty-seven soil physical, chemical, biochemical and biological attributes were quantified. The soil quality assessment was conducted using the Soil Management Assessment Framework (SMAF), using the measured soil attributes for which there are scoring curves. The total SQI, which integrates the 11 scored soil attributes, which had means ranging from 68 to 84% of optimum performance, showed that the CBTL treatment had a significantly higher SQI than the other treatments followed by RCTL > NP > CBG > RC. The row crop treatment without turkey litter amendments, RC, had the lowest overall SQI, having the lowest sector-SQI scores in all but the nutrient category. The high scores from the turkey litter treatments reflected the improved nutrient supply. Data from earlier studies indicate that the differences in the SQIs were as much due to the row crop treatments continuing to degrade the soil quality as adding back organic matter to the CBTL and RCTL treatments improved soil quality. The NP treatment has not maintained the status quo, but has seen some degradation with respect to nutrient availability, since from the early 1990s, biomass has been removed from the system resulting in some nutrient loss, especially phosphorus, which has not been supplemented by fertilizer amendments. Herbicides have also been applied during this time period, reducing plant diversity in the prairie remnant. There appeared to be a number of feedback mechanisms between nutrient availability and the enzymatic activities expressed, which measure the potential activity and optimal conditions. Enzymes were impacted not only by the nutrient(s) that serve as substrates, but also size of the microbial populations that influences the amount of enzyme produced as well as texture and bulk density, which would influence the amount of the enzyme substrate available near the location of the immobilized enzyme. The biological attributes were the most sensitive to differences the management systems. In conclusion, carefully managed pasture with additions of organic materials can improve soil quality over a row crops or grazed native prairie, dominantly through the improvements seen in nutrient availability and physical soil structure. Grazing or removing hay crops from a native plant system requires nutrient inputs maintain productivity. This work impacts land managers as they seek to restore degraded soils and policy makers involved in natural resource conservation.

Technical Abstract: Soil quality assessment is a proactive process for understanding the long-term effects of soil and crop management practices within agricultural watersheds. The objective of this study was to assess the impact of management on the soil quality in fields with 57 yrs of known management history. The fields were located near Riesel TX on the Houston Black soil series (Udic Haplusterts). We sampled five sites: an untilled native pasture (NP), two previously tilled for row crops and then seeded to coastal Bermuda grass (Cynodon dactylon (L.) Pers.) 57 (CBG) and 31 (CBTL) years ago, and two fields that have been continuously cropped (RCTL and RC). The NP and grass fields were either grazed or had grass removed as hay. Two fields, RCTL and CBTL, have had turkey litter applied for the last 6 yrs. The soil quality assessment was conducted using the Soil Management Assessment Framework, using 11 measured soil attributes. There were significant differences in overall soil quality, with CBTL functioning at about 84% of optimum, RCTL at 79%, NP at 77%, CBG at 72% and RC at 68%. When separating the soil quality index into sectors, the physical soil quality of the NP, CBTL and RCTL scored significantly higher (~83%) than the CBG and RC treatments (~66%). All treatments performed nearly the same for the chemical attributes. For the nutrient attributes, the turkey litter treatments were significantly higher than the other treatments (~95%) and NP was significantly lower (66%). The biological sector performed the worst, with the NP and CBTL performing significantly better (~72%) than the other treatments, and RC and RCTL were significantly lower (~51%). Carefully managed pasture with additions of organic materials can improve soil quality over a grazed native prairie, dominantly through the improvements seen in nutrient availability and physical soil structure. This work impacts land managers as they seek to restore degraded soils and policy makers involved in natural resource conservation.