No abstract

Infiltrating rainwater can move agricultural chemicals through soil and may contribute to contamination of drinking water supplies. Ponded infiltration rates were measured in corn (Zea mays L.) fields at four positions relative to plants and to crop rows: center of a trafficked interrow (TRK), center of an untrafficked interrow (UNT), between corn plants in a row (BPIR), and directly over the base of a plant in a row (OPIR). Measurements were taken in chisel‐plow plots during 1990 and 1991, and in no‐till plots during 1991. A Canisteo silty clay loam (fine‐loamy, mixed [calcareous], mesic Typic Haplaquoll) was the predominant soil type in the plots. In chisel‐plow plots, infiltration rates for TRK and UNT positions remained relatively constant during both years, with temporary increases after tillage or cultivation. At BPIR and OPIR positions, infiltration rates increased steadily over the growing season. Infiltration rates at the OPIR position increased from 43 to 211 µm s−1 in 1990 and from 63 to 257 µm s−1 in 1991. At the end of both growing seasons, the OPIR position had the greatest infiltration rate, and the TRK position the lowest. In no‐till, infiltration rates at all positions remained relatively constant throughout the 1991 growing season. Infiltration rates at BPIR and OPIR positions were not different from each other, were greater than 200 µm s−1, and were higher than rates at TRK and UNT positions. High potential infiltration rates in the row, especially around the bases of corn plants, have implications for the management of row‐banded chemicals.

Traffic effects on pore structure and hydraulic properties of soils may be affected by site‐specific factors. The objective of this study was to determine if the effects of wheel traffic on infiltration rates in chisel‐plow and no‐till tillage systems differed among five Midwestern locations. Ponded and unsaturated (30‐, 60‐, and 150‐mm water tension head) infiltration rates were measured sequentially using infiltrometers after removing surface residues and the upper 2 cm of soil. Wheel traffic reduced ponded infiltration rates in both tillage systems at all locations, ranging from 95% in the chisel‐plow system in Iowa to approximately 55% in the chisel‐plow system in Missouri. Tillage systems significantly affected ponded infiltration rates at only two of the locations. At the Minnesota and Nebraska locations, no‐till reduced ponded infiltration rates in untrafficked interrows by 33 and 64%, respectively, compared with those in the chisel‐plow system. Ponded infiltration rates of trafficked interrows did not differ between tillage systems at any location. At the Iowa and Nebraska locations, the decrease in infiltration rate with an increase in tension head was greater for untrafficked interrows than for trafficked interrows in the chisel‐plow system. The large pores that drain at 30 mm of tension head accounted for a lower percentage of the water flow with ponding in trafficked interrows (73%) than in untrafficked interrows (88%). Infiltration rate comparisons between tillage systems should consider wheel traffic patterns.

Soil hydraulic properties are quite variable, and characterization of field sites usually requires many measurements. One way to collect the data needed for field site characterization is to use multiple infil· trometers with automated data collection capabilities. Automated in· filtrometers use pressure transducers connected to a datalogger to measure cumulative infiltration over time. The FLOWDATA software was developed to reformat, graphically display, and analyze the large well-structured data sets collected with automated infiltrometers. Pro· gram features include interactive editing, graphing, statistical sum· maries for each infiltration data set, and pooling of estimates from multiple data sets. Inputs required are identification codes, times, transducer voltage readings, and transducer calibration files. Outputs are infiltration rates, and saturated and unsaturated hydraulic con· ductivities. Program performance is demonstrated with data from a typical field data tile.

Controlled wheel traffic is one way to manage compaction in no‐till and ridge‐till systems. This study was conducted from 1990 to 1992 at Kanawha, IA, on a Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) to examine the effect of a wheel traffic pattern on corn (Zea mays L.) root distribution, shoot growth, and yield in no‐till, ridge‐till, and chisel‐plow tillage systems. The wheel traffic pattern was configured so that some rows would have wheel tracks on both sides, on one side, or on neither side. Bulk density, hydraulic conductivity, root length density, shoot dry weight, and yield were measured at several positions across the traffic pattern. In general, the effect of tillage systems was not significant averaged across positions. Position relative to the traffic pattern had some effect, however, on all measured parameters. Bulk density was greatest in trafficked interrows (1.36 Mg m~3) and least in untrafficked interrows (1.09 Mg m−3). Hydraulic conductivity near saturation was less in trafficked (39.4 μm s−1) than in untrafficked (104.7 μm s−1) interrows. Root length density in trafficked interrows was on average one‐third of that in untrafficked interrows. Root length density in a particular interrow also was influenced by the traffic pattern in the adjacent interrows. In 2 of the 3 yr, yields of rows with a trafficked interrow on only one side were 7% less than those of rows without trafficked interrows on either side. The wheel traffic pattern, and not just the presence or absence of wheel traffic, affected corn root growth and yield.