Does drone remote sensing accurately estimate soil pH in a spring wheat field in southwest Montana?

Precision Agriculture - Soil acidification is a growing problem in semi-arid agroecosystems. In the state of Montana, USA, soil pH levels below 5.5 have been documented in nearly half of the...     

Relative Effect of Temperature and pH on Diel Cycling of Dissolved Trace Elements in Prickly Pear Creek,Montana

Diel (24 hr) cycles in dissolved metal and As concentrations have been documented in many northern Rocky Mountain streams in the U.S.A. The cause(s) of the cycles are unknown, although temperature- and pH-dependent sorption reactions have been cited as likely causes. A light/dark experiment was conducted to isolate temperature and pH as variables affecting diel metal cycles in Prickly Pear Creek, Montana. Light and dark chambers containing sediment and a strand of macrophyte were placed in the stream to simulate instream temperature oscillations. Photosynthesis-induced pH changes were allowed to proceed in the light chambers while photosynthesis was prevented in the dark chambers. Water samples were collected periodically for 22 hr in late July 2001 from all chambers and the stream. In the stream, dissolved Zn concentrations increased by 300% from late afternoon to early morning, while dissolved As concentrations exhibited the opposite pattern, increasing 33% between early morning and late afternoon. Zn and As concentrations in the light chambers showed similar, though less pronounced, diel variations. Conversely, Zn and As concentrations in the dark chambers had no obvious diel variation, indicating that light, or light-induced reactions, caused the variation. Temperature oscillations were nearly identical between light and dark chambers, strongly suggesting that temperature was not controlling the diel variations. As expected, pH was negatively correlated (P < 0.01) with dissolved Zn concentrations and positively correlated with dissolved As concentrations in both the light and dark chambers. From these experiments, photosynthesis-induced pH changes were determined to be the major cause of the diel dissolved Zn and As cycles in Prickly Pear Creek. Further research is necessary in other streams to verify that this finding is consistent among streams having large differences in trace-element concentrations and mineralogy of channel substrate.     

Response of Malt Barley to Phosphorus Fertilization Under Drought Conditions

ABSTRACT

Drought conditions are common in the northern Great Plains of the United States, affecting crop yield and quality. Phosphorus (P) fertilizer applications have been found to increase drought tolerance, although there is a lack of published work in this area. The goal of this study was to determine the effects of P fertilization on drought tolerance in malt barley (Hordeum vulgare). Here, 60 cm tall PVC columns were filled with either a silt loam that had a medium soil test phosphorus (STP) level or with the same soil diluted 1:1 (v/v) with coarse sand (low STP). Monoammonium phosphate was incorporated into the surface soil at rates equating to 0, 7.5, and 25 kg P ha^{? 1} (in triplicate), seeded with malt barley, and watered to maintain water contents either slightly above –1.5 MPa (dry treatment) or slightly drier than field capacity (wet control). Fertilization with P significantly increased plant biomass, root biomass, grain yield, and water-use efficiency (WUE) in the medium STP soil, but not in the low STP soil. Growth in the low STP, coarse, dry soil was apparently limited by water, not P, based on comparisons with the wet control. Fertilization of the dry medium STP soil with P increased grain yield by at least 20-fold, although this increase was not significant due to high variability. These results suggest that adequate soil P levels can substantially offset the impact of drought on barley growth and grain yield.     

Role of Hydrous Iron Oxide Formation in Attenuation and Diel Cycling of Dissolved Trace Metals in a Stream Affected by Acid Rock Drainage

Mining-impacted streams have been shown to undergo diel (24-h) fluctuations in concentrations of major and trace elements. Fisher Creek in south-central Montana, USA receives acid rock drainage (ARD) from natural and mining-related sources. A previous diel field study found substantial changes in dissolved metal concentrations at three sites with differing pH regimes during a 24-h period in August 2002. The current work discusses follow-up field sampling of Fisher Creek as well as field and laboratory experiments that examine in greater detail the underlying processes involved in the observed diel concentration changes. The field experiments employed in-stream chambers that were either transparent or opaque to light, filled with stream water and sediment (cobbles coated with hydrous Fe and Al oxides), and placed in the stream to maintain the same temperature. Three sets of laboratory experiments were performed: (1) equilibration of a Cu(II) and Zn(II) containing solution with Fisher Creek stream sediment at pH 6.9 and different temperatures; (2) titration of Fisher Creek water from pH 3.1 to 7 under four different isothermal conditions; and (3) analysis of the effects of temperature on the interaction of an Fe(II) containing solution with Fisher Creek stream sediment under non-oxidizing conditions. Results of these studies are consistent with a model in which Cu, Fe(II), and to a lesser extent Zn, are adsorbed or co-precipitated with hydrous Fe and Al oxides as the pH of Fisher Creek increases from 5.3 to 7.0. The extent of metal attenuation is strongly temperature-dependent, being more pronounced in warm vs. cold water. Furthermore, the sorption/co-precipitation process is shown to be irreversible; once the Cu, Zn, and Fe(II) are removed from solution in warm water, a decrease in temperature does not release the metals back to the water column.