Legacy effects of temporary grassland in annual crop rotation on soil ecosystem services.

The introduction of temporary grassland into an annual crop rotation is recognized to improve soil ecosystem services, and resulting legacies can be beneficial for the following crops. In this context, the aim of the present study was to evaluate legacy effects of introducing temporary grassland into an annual crop rotation on five ecosystem services (i) soil structure maintenance (aggregate stability), (ii) water regulation (saturated hydraulic conductivity), (iii) biodiversity conservation (microbial biomass and microbial metabolic activity, as well as microorganism, enchytraeid, springtail and earthworm communities), (iv) pathogen regulation (soil suppressiveness to Verticillium dahliae), and (v) forage production and quality. Three crop rotation schemes, maintained for twelve years, were compared in four random blocks, one being an annual crop rotation without grassland (0%), another with a medium percentage of grassland (50%, corresponding to 3 years of continuous grassland in the crop rotation), and a third one with a high percentage of grassland in the crop rotation (75%, corresponding to 6 years of continuous grassland in the crop rotation). The results showed that the grassland introduction into an annual crop rotation improved, whatever the duration of the grassland, soil structure maintenance and biodiversity conservation, while it decreased pathogen regulation and did not modify water regulation. Comparing the two crop rotations that included grassland, indicated a stronger beneficial grassland legacy effect for the higher proportion of grassland concerning soil structure maintenance and biodiversity conservation. By contrast, water regulation, pathogen regulation and forage production were not affected by the legacy of the 75% grassland during the rotation. Overall, our findings demonstrated the extent to which grassland legacies are affecting the current state of soil properties and possible ecosystem services provided. To improve ecosystem services, soil management should take legacy effects into account and consider longer timeframes to apply beneficial practices.

Discrimination of farm waste contamination by fluorescence spectroscopy coupled with multivariate analysis during a biodegradation study.

The persistence of potential tracers of dissolved organic matter (DOM) generated from farm waste-amended soil was investigated by fluorescence spectroscopy coupled with classification and regression tree (CART) and principal component analysis (PCA) during a short-term (8 days) to midterm (60 days) biodegradation study. Pig manure (PM), cow manure (CM), wheat straw (WS), and soil alone (SA) treatment inputs were used. Waste amendments were potential sources of higher DOM concentrations. PCA revealed the DOM quality differences between farm wastes and soil alone as well as a significant shift observed from the biochemical to the geochemical fluorescent fraction in SA and PM treatments. The tryptophan:Humic-Like ratio and tryptophan zone were the potential discriminators of recent and midterm pollution by farm wastes. Integral intensities of the Fulvic-Like zone and region III discriminated the PM from CM and WS during the 60 days. CART analysis showed 90 and 100% potential for farm wastes discrimination from soil during P1 and P2, respectively. The prediction successes were 72 and 57% for PM from other wastes and 60 and 100% for WS during both periods. Fluorescence spectroscopy in combination with CART analysis can be a nondestructive innovative method for monitoring susceptible farm waste contamination.

Sorption of aged dicamba residues in soil.

The effect of aging (residence time in soil) on dicamba (3,6-dichloro-2-methoxybenzoic acid) and a major metabolite, 3,6-dichlorosalicylic acid (3,6-DCSA) sorption was determined in an unamended and a carbon-amended sandy loam and in a silt loam soil. During the incubation, sequential solvent extraction with 0.01 M calcium chloride solution and aqueous acetonitrile + hydrochloric acid was used to determine the solution and sorbed concentrations of dicamba and 3,6-DSCA, and sorption coefficients were calculated. Dicamba was weakly sorbed to soil (Kd < 0.7). In contrast to some other classes of pesticides, sorption of dicamba did not significantly increase with aging, at least not until < 15% of the applied dicamba remained. 3,6-DSCA was strongly sorbed to soil (Kd > 8) and the Kd-a value increased by a factor of 2-6 during a 28-day aging period. Addition of a carbon source to the soil had minimal effect on the strength of sorption of aged dicamba. However, it did appear to decrease 3,6-DSCA availability to soil micro-organisms; once formed 3,6-DSCA was not further mineralized. While it appears that sorption can be well characterized for weakly sorbed pesticides using the batch equilibration method with freshly treated soils, this procedure may not be adequate for more strongly sorbed pesticides and their degradates.