No abstract

Portable x-ray fluorescence (pXRF) technology can be implemented in soil geochemical analysis for faster and more efficient testing of trace metals in soils. The level of soil phosphorus (P) is one of the major indicators of human activities related to food distribution, preparation, and waste disposal. Unfortunately, the low x-ray energy level of P and other light elements requires extensive sample preparation that may preclude pXRF as a field laboratory tool for P measurement. The high silicon content of soil causes serious interference in P analysis, yielding data of little value in midden prospection or activity area analysis. The Mehlich II or the Olsen bicarbonate extraction of soil samples can be conducted in a field laboratory providing excellent quality data. For pXRF analysis of soil samples in the field laboratory, it is recommended that soils are air-dry, and aggregates crushed, sieved (<2 mm), and mixed for better accuracy and reproducibility. Gridded soil samples from the central plaza of Telchaquillo, a contemporary village in Yucatan, were analyzed by the Mehlich II method for P and by pXRF and DTPA (diethylenetriaminepentaacetic acid) chelate extraction for trace metal concentrations. Areas of high P concentration were associated with an eatery and with two butchering posts. High DTPA extractable iron, copper, zinc, and manganese concentrations near the butchering posts were likely associated with the remnants of blood from butchered animals. The distributions and locations of elevated Fe concentrations were different for DTPA extractable Fe and pXRF total Fe and can be attributed to the different forms and solubility of crystalline iron in soil.

The use of alternative N sources relative to conventional ones could mitigate soil-surface NO emissions. Our objective was to evaluate the effect of anhydrous ammonia (AA), urea, and polymer-coated urea (ESN) on NO emissions for continuous corn ( L.) production. Corn received 110 kg N ha in 2009 and 180 kg N ha in 2010 and 2011. Soil NO fluxes were measured one to three times per week early in the growing season and less frequently later, using vented non-steady state closed chambers and a gas chromatograph. Regardless of N source, NO emissions were largest immediately after substantial (>20 mm) rains, dropping to background levels thereafter. Averaged across N sources, 2.85% of the applied N was lost as NO. Emission differences for treatments only occurred in 2010, the year with maximum NO production. In the 2010 growing season, cumulative emissions (in kg NO-N ha) were lowest for the check (2.21), followed by ESN (9.77), and ESN was lower than urea (14.07) and AA (16.89). Emissions in 2010 based on unit of corn yield produced followed a similar pattern, and NO emissions calculated as percent of applied N showed that AA losses were 1.9 times greater than ESN. Across years, relative to AA, ESN reduced NO emissions, emissions per unit of corn yield, and emissions per unit of N applied, whereas urea produced intermediate values. The study indicates that, under high N loss potential (wet and warm conditions), ESN could reduce NO emissions more that urea and AA.

Sufficient soil moisture is crucial for corn (Zea mays L.) germination and emergence. As within‐field soil moisture varies, it is often expected that corn seeding depth should vary accordingly. As seedbeds get drier, deeper planting increases the chances of higher soil moisture and faster emergence. The goal was to evaluate the corn yield response to shallow and deep seeding depths compared with the standard seeding depth while making use of management zones delineated using relative elevation data as surrogate of spatial patterns of soil moisture. We hypothesize that crop yield responds positively to shallow seeding depth in zones with low relative elevation values, wet zones, whereas the opposite would be expected in drier zones in a range of locations across the U.S. Midwest. Landscape position (LSP) values (i.e., relative elevation values) were computed from LIDAR data and used to approximate the spatial soil moisture distribution by splitting variability into dry, transitional, and wet LSP zones. Field‐long strips were planted in 17 commercial fields in 2014 and 2015 at shallow, standard, and deep seeding depths. The LSP zones were a significant predictor of the yield response to shallow or deep seeding depth only in 5 and 2 out of 17 field‐years, respectively. Significant overall responses of yield to shallow or deep seeding depth were found in 6 and 8 out of 17 field‐years, respectively. The yield response to variable seeding depth of corn showed high field‐specificity and was likely attenuated by favorable conditions for corn planting and during the growing seasons.