Measuring Wind and Low-Relief Topographic Effects on Rainfall Distribution

Advances in agricultural technology are giving farmers the capability to selectively manage soils of smaller and smaller areal dimension, and the capacity to alter management practices on the go. Farmers need to better understand the nature of within-field variability if they are to adjust their management accordingly. We hypothesized that wind interacts with low-relief topographic features and significantly alters rainfall distribution in the landscape. To determine wind and topographic effects on rainfall distribution across agricultural landscapes, rainfall intensity measurements have typically been made in situ. Problems associated with this method involve finding appropriate field sites, observational uncertainties, and logistical complications. For a study of rain on low hills, we avoided such problems by using a full-sized replica of a hill. Design and construction of this hill model are described. The apparatus emulated the slope and summit components of a low hill, and summit elevation was adjustable [1 to 3 m (3 to 10 ft)]. It was equipped with wind speed and direction sensors, and tipping-bucket flow-gages that measured natural precipitation intercepted by catchments located on windward and leeward slope positions. It automatically maintained a windward orientation during precipitation events, thus increasing the number of relevant measurements obtained in a given season. Results, obtained over two field seasons, indicate that hydrological rainfall varied significantly across different portions of the hill model. On average, hill positions experiencing maximum intensity received 1.5x more rain than those positions with the least precipitation. The rainfall pattern differed, depending on meteorological rainfall (intensity measured on level ground beyond the hill model), incident wind speed, and hill-summit elevation. This study shows that rainfall can vary across landscapes that include low-relief topographic features. The amount of variation is large enough to influence crop or plant growth, and other soil processes

Soil property patterns and topographic parameters associated with ephemeral gully erosion

The pattern of ephemeral gully erosion and associated soil properties were investigated in three southeastern Minnesota soilscapes during 1988 and 1989. The associations between topographic attributes and erosion characteristics of sample sites were also examined. No ephemeral erosion was measured after the investigation began in the drought year of 1988. In 1989 soil lost from ephemeral gullies ranged from 0.8 to 1.6 Mg/ha (.4 to .7 ton/ac) at the study sites, or one-tenth of that reported in the literature for similar watersheds. Pre-1988 data available at one site showed that soil voidage was an order of magnitude greater during the wetter-than-normal 1986 season. A simple erosion model predicting topsoil removal and subsoil mixing in upper reaches and deposition in lower ephemeral gully reaches, does not accurately describe erosion processes in these landscapes. Impact of ephemeral erosion on soil properties in landscapes varied depending on relative 1) rill and interrill contributions, 2) proclivity for channel drifting, and 3) occurrence of depositional sorting in channels. Topographically sensitive controls of ephemeral erosion, such as surface saturation and stream transport capacity, played different roles in channel formation at each site. Topographic indices most useful for predicting ephemeral erosion were planform curvature, profile curvature•slope, Ln (unit area/slope), unit area•slope, and planform curvature•upstream contributing area•slope

Soil property patterns and topographic parameters associated with ephemeral gully erosion

The pattern of ephemeral gully erosion and associated soil properties were investigated in three southeastern Minnesota soilscapes during 1988 and 1989. The associations between topographic attributes and erosion characteristics of sample sites were also examined. No ephemeral erosion was measured after the investigation began in the drought year of 1988. In 1989 soil lost from ephemeral gullies ranged from 0.8 to 1.6 Mg/ha (.4 to .7 ton/ac) at the study sites, or one-tenth of that reported in the literature for similar watersheds. Pre-1988 data available at one site showed that soil voidage was an order of magnitude greater during the wetter-than-normal 1986 season. A simple erosion model predicting topsoil removal and subsoil mixing in upper reaches and deposition in lower ephemeral gully reaches, does not accurately describe erosion processes in these landscapes. Impact of ephemeral erosion on soil properties in landscapes varied depending on relative 1) rill and interrill contributions, 2) proclivity for channel drifting, and 3) occurrence of depositional sorting in channels. Topographically sensitive controls of ephemeral erosion, such as surface saturation and stream transport capacity, played different roles in channel formation at each site. Topographic indices most useful for predicting ephemeral erosion were planform curvature, profile curvature•slope, Ln (unit area/slope), unit area•slope, and planform curvature•upstream contributing area•slope

Crop Rotation and Soil Amendment Alters Sorghum Grain Quality

Soybean [Glycine max (L.) Merr.] rotation enhances grain sorghum [Sorghum bicolor (L.) Moench] yield, but infl uence on grain quality has not been measured. The objective was to determine the effect of cropping sequence (CS) and soil amendment (SA) on grain yield and quality. Sorghum grain yield and quality, soil NO3–N and water were measured in a rotation study in 2003 and 2004 on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll). Cropping sequences were continuous sorghum, and sorghum rotated with non-nodulating and nodulating soybean. Soil amendments consisted of no amendment, manure (17–26 Mg dry matter ha−1 yr−1), and N (84 kg ha−1 yr−1). CS × SA interaction effects were found for most parameters. Rotation with non-nodulating soybean without SA increased yield by 2.6 to 2.8 Mg ha−1 over continuous sorghum without SA. Rotation without SA with nodulating soybean further increased yield by 1.7 to 1.8 Mg ha−1 over rotation with non-nodulating soybean. Grain N increased by 0.5 to 1.0, 2.5 to 5.0, and 3.3 to 4.9 g kg−1 for N application to continuous sorghum and sorghum rotated with non-nodulating and nodulating soybean, respectively. Tangential abrasive dehulling device (TADD) removal indicated that continuous sorghum without SA produced the softest grain with 43 to 44% TADD removal, and sorghum rotated with nodulating soybean with manure produced the hardest grain with 22 to 27% TADD removal. As food end-use opportunities for sorghum grain evolve, use of crop rotation and SA application will be important to produce grain with desirable quality attributes. Includes corrected Table 4