Effects of cover crops on soil quality: Part I. Soil chemical properties—organic carbon, total nitrogen, pH, electrical conductivity, organic matter content, nitrate-nitrogen, and phosphorus

Abstract

Cover cropping in association with row crop rotation has been suggested as a favorable conservation practice in improving soil chemical characteristics. The main objective of this research was to investigate the effects of growing cover crops under conservation tillage on soil organic carbon (C), total nitrogen (N), pH, electrical conductivity (EC), soil organic matter (SOM) content, nitrate-nitrogen (NO₃-N), and phosphorus (P) in different surface cover treatments, including (1) cover crop only without seed maize (Zea mays L.) or soybean (Glycine max L.) residue (CC), (2) cover crop mixtures planted in seed maize or soybean residue (SCCC), (3) seed maize or soybean residue only without cover crops (SC), and (4) bare soil. Field research was conducted from 2012 to 2015 on three center pivot-irrigated, seed maize/soybean cover crop rotation, large-scale production fields near Beaver Crossing, Nebraska. Changes in soil chemical properties exhibited variation between the treatments and between the soil layers within the same treatment as well as between the years. Inclusion of continuous cover cropping resulted in small increases of organic C and total N only in the top 0 to 5 cm soil depth in the SCCC treatment. During the winter period when cover crops were winter-killed and decomposed onto the soil surface, both C and N concentration in the topsoil (0 to 5 cm) SCCC plots had increased by 8% and 21%, respectively, and in the CC plots by 10% and 5%, respectively. Although cover crops are highly decomposable, an increase in SOM levels following cover crops was only limited to the topsoil (0 to 20 cm). Soil organic matter under cover cropped plots in the 0 to 5 cm soil layer was 28% higher than the bare soil treatment. Cover crops significantly (p < 0.05) reduced P and NO₃-N quantities in the soil when they were alive and actively growing; however, they also contributed to providing N and P to the next maize crop by residue decomposition in winter. There was no significant (p > 0.05) change in soil pH among treatments. Cover cropped treatments had decreased soil EC at all soil layers and ranged from 7.3% decrease to 74% decrease from the beginning to the end of the research. This research showed that SOM, NO₃-N, P, C, and N can be at least conserved or maintained and/or enhanced (primarily in the topsoil) by cover crop species researched, and thus, can contribute to improving the soil quality and, in turn, potentially improve crop productivity. However, it is important to note that most of the changes in soil chemical properties as a result of incorporating cover crops in the rotation appeared to be confined in the topsoil.