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Recent increases in corn (Zea mays L.) production in the U. S. Corn Belt have necessitated the conversion of rotations to continuous corn, and an increase in the frequency of tillage. The objective of this study was to assess the effect of rotation and tillage on soil physical and chemical properties in soils typical of Illinois. Sequences of continuous corn (CCC), 2-yr corn-soybean [Glycine max (L.) Merr.] (CS) rotation, 3-yr corn-soybean-wheat (Triticum aestivum L.) (CSW) rotation, and continuous soybean (SSS) were split into conventional tillage (CT) and no-till (NT) subplots at two Illinois sites. After 15 yr, bulk density (BD) under NT was 2.4% greater than under CT. Water aggregate stability (WAS) was 0.84 kg kg-1 under NT compared to 0.81 kg kg-1 under CT. Similarly, soil organic carbon (SOC) and total nitrogen (TN) were greater under NT than under CT with SOC values for 0 to 60 cm of 96.0 and 91.0 Mg ha-1 and TN values of 8.87 and 8.40 Mg ha-1 for NT and CT, respectively. Rotations affected WAS, TN, and K levels with WAS being greatest for the CSW rotation at 0.87 kg kg-1, decreasing with more soybean years (CS, 0.82 kg kg-1 and SSS, 0.79 kg kg-1). A similar pattern was detected for TN and exchangeable K. Results indicated that while the use of NT improved soil quality, long-term implementation of continuous corn had similar soil quality parameters to those found under a corn-soybean rotation. [ABSTRACT FROM AUTHOR]

During transition to organic production, various strategies can be implemented to enhance soil health, including the soil property of disease suppressiveness. We previously found increased levels of diseases caused by biotrophic pathogens associated with manure application, but manure also suppressed diseases caused by necrotrophic pathogens. In an extension of that study we evaluated soils from different cropping system and organic amendment treated plots using a bioassay of suppressiveness to two soilborne diseases, Rhizoctonia root rot and sudden death syndrome (SDS) of soybean [Glycine max (L.) Merr.]. Also, the soil population levels of Pseudomonadaceae were assessed for their suitability as an indicator of disease suppressiveness. Levels of soil suppression of both Rhizoctonia root rot and SDS were found to be associated with specific cropping systems, but the associations were not consistent from year to year. There were no associations between organic amendment treatments and disease suppression in the bioassay studies. However, there was an overall increase in soil suppressiveness to Rhizoctonia solani during the 3 yr of transition, regardless of cropping system or organic amendment treatments. In contrast, there was an overall decrease in suppressiveness to Fusarium virguliforme during the transition. There was no significant effect of cropping system or organic amendment treatments on the levels of Pseudomonadaceae, indicating that this was not a good predictor of general suppression in this study. While specific treatments were not found to consistently impact soil suppressiveness, the overall increase in suppressiveness to R. solani during the 3-yr transition did show the value of the transition process. [ABSTRACT FROM AUTHOR]

Expansion of the agricultural frontier over marginal soils leaves a significant environmental imprint on the southern semiarid region of the Argentina pampas. A chronosequence of anthropogenic soils in a cultivated area was investigated to determine the role of human actions on the development of a highly compacted horizon below the plow layer observed during a detailed soil survey in Villarino County. A model area of 300 ha (6 x 0.5 km) representative of the county soilscapes was used to (i) characterize the main physical, chemical, and morphological features of the soils in the chronosequence, and (ii) discuss taxonomical issues that can be improved on to facilitate information transfer. Based on our observations, we propose a new diagnostic feature to classify these soils according to USDA Soil Taxonomy guidelines placed at a taxonomical level above series. Our investigation confirmed that soil morphology is modified within 27 yr of cultivation. Tillage leads to the development of a noncemented plowpan immediately below the Ap, here called ACd, with distinctive morphological features. The ACd is compact and massive with extremely hard rupture resistance when dried. Cultivation-induced alterations were considered important enough to classify the soils into unique soil series. Given the widespread environmental and financial costs and implications of soil compaction, and the genetic connotations of the plowpan, we propose the densipan as a diagnostic horizon and a new class densic to be use at the family level. Advantages of its use will lead to increased utility and precision in published soil maps and improved communication and understanding among stakeholders. [ABSTRACT FROM AUTHOR]