Soil temperature distribution and heat transfer affect crop development as well as water and solute transfers in the vadose zone. The objective of this study was to characterize seasonal soil temperature distribution throughout a rice-growing season in an eastern Arkansas soil typically cropped to rice. Soil temperature (T) measurements and climatic parameters were taken every 30 min throughout the season. T was measured in a layered calloway silt loam (fine-silty, mixed, thermic, Aquic Fragiudalfs) at nine different depths from the soil surface to 1 m. Results indicated that average daily soil T varied throughout the season at all recording depths (e.g., from 14.2 °C to 29.3 °C at 0.14 m and from 13 °C to 24.9 °C at 1 m). Diurnal soil T amplitude was reduced, and T phase shift increased by an additional 3 h at 0.05 m and by 5 h at 0.14 m and 0.26 m (when compared with air temperatures) on field flooding and increased canopy cover. Heat transfer was modeled using the onedimensional Fourier equation, solved using the finite element method of the mathematical software MATLAB. Predicted T (Tp) were in close agreement with measured T (Tm) at all depths in the soil profile when two constant values of thermal diffusivity (α) were used for the soil profile: α = 4.58E-7 m2 s−1 in the Ap1 horizon and α = 4.86E-7 m2 s−1 in the rest of the soil profile. Differences between Tp and Tm were always lower than 1.04 °;C for all periods considered.
The effectiveness of management practices in improving quality of runoff from agricultural land areas hasbeen reported based primarily on results from plot- and field-scale studies. There is limited information available onwatershed scales, particularly when the dominant agricultural land use is pasture. The objective of this study was todetermine whether a program of Best Management Practice (BMP) implementation in the Lincoln Lake watershed ofnorthwestern Arkansas was effective in reducing storm stream flow concentrations and mass transport of nitrate nitrogen(NO3-N), ammonia nitrogen (NH3-N), total Kjeldahl nitrogen (TKN), ortho-phosphorus (PO4-P), total phosphorus (TP),chemical oxygen demand (COD), and total suspended solids (TSS). Storm flow quality of the two main tributaries toLincoln Lake was monitored from September 1991 to April 1994. Significant decreases (from 23 to 75% per year) in bothconcentrations and mass transport of NO3-N, NH3-N, TKN, and COD occurred concurrently with BMP implementation.The decreases in nitrogen and COD concentrations and mass transport are attributed to BMP implementation, and theBMP most responsible for these decreases is most likely nutrient management.
The absorption of 14 C-labeled herbicides by soybean ( Glycine max (L.) Merr. ‘Lee’) seed from aqueous solutions and treated soil was investigated. A comparison of the absorption of the various herbicides from aqueous solution showed that differences existed in the rate and amount of herbicide absorbed by the seed. Calculations showed that the concentration of herbicides at the seed coat surface varied with absorption time which indicated that the permeability of the soybean seed to these herbicides changed during the absorption process. The rate of absorption of isopropyl m -chlorocarbanilate (chlorpropham) and 2-chloro-4-(ethylamino)-6-(iso propylamino)- s -triazine (atrazine) by soybean seed in soil was rapid for the first 4 hr and then decreased steadily until the event of germination at which time the rate increased. When the amount absorbed by the soybean was compared with that predicted by the perfect sink equation, it was found that the soybean was a better sink during the first few hours than afterwards. The amount of herbicide moved to the seed in the imbibed water could not account for the total amount of chlorpropham absorbed indicating considerable contributions from diffusive transport. Only during the initial 4-hr period was uptake of atrazine greater than that moved to the seed by mass flow.
Abstract Knowledge of N and P uptake and translocation is essential for a greater understanding of soybean [Glycine max (L.) Merrill] nutrient relations under flooding conditions. A field experiment was conducted on a Crowley silt loam (Typic Albaqualf) to determine N and P uptake and translocation rates in soybean under flooded and non‐flooded conditions. Forrest soybean were flooded at the R? growth stage for 7 consecutive days at a flood height of 2.5 cm. The soybean were partitioned into stems, branches, leaves, and pods at 0, 7, 14, 21, 36, and 62 days after flooding. Dry matter, N and P concentrations, and total amounts of N and P accumulated for each compartment were determined at each sampling time. Calculations of whole plant uptake and translocation rates of N and P were made of the plant parts and of the nodes during the five intervals. The leaves and then the branches were the first plant parts to respond to the prolonged flooding. Leaves of the flooded plants had a greater decrease in N fluxes than the other plant parts. During the flood, N fluxes were negative in the middle nodes and positive in the upper nodes which indicated that N was translocated from the middle to the upper canopy without substantial replenishment from the flooded soil. Higher P fluxes were found in the pods and whole plants in flooded soybean as compared to non‐flooded controls. In both treatments and for both elements, the highest elemental fluxes occurred between the stems and pods which indicated that the pods were the main sink for both N and P. The magnitude of transport coefficients for both elements and in both treatments indicated that the main transport pathway during early reproductive growth was from stems to branches. During late reproductive growth the main transport pathway was from the stems to the pods. The redistribution of N within soybean plant parts was greater than that of P.
