FALL CONTOUR RIPPING INCREASES WATER INFILTRATION INTO FROZEN SOIL

Crop residue management to trap snow and soil management to improve wa ter infiltration into frozen soil might reduce spring runoff and incre ase soil water storage. We hypothesized that soil macropores created b y tillage would improve water infiltration when the soil was frozen. T his hypothesis was tested by ripping a Dooley sandy loam (fine-loamy, mixed Typic Argiboroll) in the fall of the year and then measuring wat er infiltration when the soil was frozen. A single subsoiling shank wa s used to rip soil to a depth of 0.3 m at 6-m contour intervals. Rippi ng was compared with no ripping using a randomized experimental design having three replications, Studies were conducted during 4 yr near Cu lbertson, MT, on plots seeded annually to spring wheat (Triticum aesti vum L.). Soil water was measured,vith neutron attenuation and gravimet ric methods. We used a constant-head (100 mm) method to measure water infiltration into frozen soil and a rainfall simulator for unfrozen su it. Final infiltration rate on frozen, ripped soil averaged 16 vs. 2 m m h(-1) without ripping, Final unfrozen infiltration rate in spring wa s 34 mm h(-1) with ripping vs. 15 mm h(-1) without ripping, Average sp ring water content of the top 1.2 m of soil, to a distance 1.5 m downs lope from a rip, was 32 mm greater with ripping than without ripping a t comparable slope positions. There were no wheat yield differences be tween treatments.