Conservation and storage of snowmelt in stubble land and fallow under alternate fallow-strip cropping management in Montana

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The purpose of this 3-year study was to learn more about the efficiency of stubble in augmenting soil water storage from snow entrapment on small grain farms under alternate crop-fallow management in Montana. Nearly all the precipitation that falls during the winter period in the study area occurs in the form of snow. The term, snowmelt recharge efficiency (SRE), is used to indicate over-winter increase in soil water expressed as a percent of the total winter precipitation. This experiment was conducted on established fields under alternate fallow-strip cropping management in Montana during three winters (1976–1977, 1977–1978, 1978–1979) at 6, 7 and 7 sites, respectively, extending over a north-south distance of ∼320 km. About half of the sites were located in climatic areas characterized by relatively low chinook frequency and half in areas of high chinook frequency. There were three treatments: fallow, standing half stubble and standing full stubble. Soil water was measured to the 1.2-m depth in the autumn and again in the spring to compare the performance of the treatments in amount of soil water gain during the over-winter period. The study showed that SRE is significantly higher on the stubble treatments than on fallow. Since autumn soil water tends to be less in stubble than in fallow, much of the difference in SRE between fallow and stubble is attributed to the differences in autumn soil water levels. In the spring following the relatively dry first winter, there was still significantly less water in the soil in stubble areas than in fallow, but following the two wet winters there was no significant difference. The larger SRE for stubble treatments during the dry winter indicates that more water entered the soil in stubble than in fallow, but recovery of soil water in stubble was not enough to completely recharge the soil profile. In the two wet winters, there was such an abundance of water in all treatments that the autumn soil water deficit in stubble was fully recovered. While the increase in SRE in these wet years was due to the complete recovery of the autumn soil water deficit, it is not clear whether this deficit would have completely recovered had the stubble not been left standing. This study also revealed differences in SRE between climatic areas of relatively low and high chinook frequency that were near the 5% level of significance during the first winter and at the 1% level during the third winter. SRE was generally greater in climatic areas characterized by few chinooks compared with areas of greater chinook frequency. While this difference may be partially due to chinook-related climatic conditions, initial soil water amounts in the autumn and/or other edaphic or climatic differences are probable contributing factors.