Temporal stability in soil water content patterns across agricultural fields

When a field or a small watershed is repeatedly surveyed for soil water content, locations can often be identified where soil water contents are either consistently larger or consistently less than the study area average. This phenomenon has been called temporal stability, time stability, temporal persistence, or rank stability in spatial patterns of soil water contents. Temporal stability is of considerable interest in terms of facilitating upscaling of observed soil water contents to obtain average values across the observation area, improving soil water monitoring strategies, and correcting the monitoring results for missing data. The objective of this work was to contribute to the existing knowledge base on temporal stability in soil water patterns using frequent multi-depth measurements with Multisensor Capacitance Probes (MCPs) installed in a coarse-texture soil under multi-year corn production. Water contents at 10, 30, 50, and 80 cm depths were measured every 10 min for 20 months of continuous observation from May 2001 to December 2002. The MCPs revealed temporal stability in soil water content patterns. Temporal stability was found to increase with depth. The statistical hypothesis could not be rejected (P < 0.0001) that data collected each 10 min, each 2 h, each day, and each week had the same temporal stability. The locations that were best for estimating the average water contents were different for different depths. The best three locations for the whole observation period were the same as the best locations for a month of observations in about 60% of the cases. Temporal stability for a specific location and depth could serve as a good predictor of the utility of this location for estimating the area-average soil water content for that depth. Temporal stability could be efficiently used to correct area-average water contents for missing data. Soil water contents can be upscaled and efficiently monitored using the temporal stability of soil water content patterns.     

Multi-Year Measurements of Field-Scale Metolachlor Volatilization

Volatilization is a critical pathway for herbicide loss from agricultural fields, and subsequently deposited downwind from the edge of the field. To better understand the volatilization process, field-scale turbulent volatilization fluxes of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide) were quantified for 13 consecutive years using a combination of herbicide concentration profiles and eddy diffusivities derived from turbulent fluxes of heat and water vapor. Site location, type of herbicides, and agricultural management practices remained unchanged during this study in order to evaluate the effect of soil moisture on metolachlor volatilization. Twenty gravimetric surface soil moisture samples (0–5 cm) were collected immediately after herbicide application and then at 0430 hours each morning to determine the impact of surface moisture on herbicide volatilization. Five days after application, cumulative herbicide volatilization ranged from 5 to 63% of that applied for metolachlor. Metolachlor volatilization remained an important loss process more than 5 days after application when the soil surface was moist. Conversely, if the soil surface was dry, negligible volatilization occurred beyond 5 days. Furthermore, the total amount of metolachlor volatilized into the atmosphere increased exponentially with surface soil water content during application (r ²?=?0.78). Metolachlor volatility was found to be governed largely by surface soil moisture.     

Aphids detect approaching predators using plant-borne vibrations and visual cues

Journal of Pest Science - Aphids (Hemiptera: Aphididae) have a repertoire of defensive behaviors against insect predators and parasitoids that includes kicking, twitching, walking away and dropping...     

The dispute over wild rice: an investigation of treaty agreements and Ojibwe food sovereignty

The treaties established between the United States federal government and American Indian nations imply U.S. recognition of Native political sovereignty. Political sovereignty encompasses not only the ability to govern oneself but also self-determination regarding resource use, including food. This paper addresses The White Pine Treaty of 1837, which acknowledges the Ojibwe people’s right to hunt, fish, and harvest wild rice in their traditional landscape. This acknowledgement by extension recognizes the Ojibwe’s right to food sovereignty. From the perspective of the Ojibwe, continuing these activities requires not simply controlling access to important food resources but also protecting their rights to maintain traditional relationships with the plants and animals that provide food and to manage the landscapes that provision them. Therefore, true food sovereignty necessitates protecting a people’s relationships with the landscape. Appropriation of wild rice over the past century, however, has threatened food sovereignty among the Ojibwe because it has compromised their ability to maintain their traditional relationship with a staple food resource that is also central to their identity. In light of the White Pine Treaty, this threat to the Ojibwe’s food sovereignty is effectively a threat to their political sovereignty and, we argue, a violation of the treaty agreement.