Moisture conservation and use at Swift Current – a comparison to previous findings
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The results of an ongoing 18-year crop rotation study at Swift Current were compared to those reported 30-40 years earlier. The two periods showed no difference in over winter moisture conserved for stubble or fallow-systems. Moisture conserved in the 9 months (fall and winter) period on stubble was 34 % of the precipitation received in this period while 18 % of precipitation received in the 21 month fallow period was conserved. These compare w1th earlier reports for these two periods which were 33 and 21 %, respectively. The 18-year average moisture use efficiency for the current study averaged between 6.9 kg ha-1 mm-1 moisture used (mu) for fallow-seeded wheat and a low of 5.1 kg ha-1 mm-1 for continuous wheat that received P but no N fertilizer annually. Here mu was defined as spring soil moisture - Harvest soil moisture plus precipitation received from May 1 to August 31. These efficiencies for the more recent period were much higher than those reported by Staple and Lehane for the period of 1939-1950 where fallow wheat would produce 4.5 kg ha-1 mm-1 and stubble-wheat produce 3.7 kg ha-1 mm-1. The relationship between yield and mu for stubble crops was best described by a quadratic model while a linear model best fit the fallow crop data, The equation for the fallow system for the recent study was y = -397 + 8.69 mu (r=0.77**), while Staple and Lehane reported y = -1298 + 9.32 mu (r=0.83**). These equations suggest that the rate of increase per mm of mu are approximately the same for the two periods studied, but that in more recent times wheat is making more efficient use of smaller amounts of moisture. For example, while Staple and Lehane predict that 139 mm of moisture was required to produce 1 kg ha-1 of grain, we find that only 46 mm is now required for fallow-seeded wheat to produce 1 kg ha-1.
Part OfSoils and Crops Workshop
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