Water use efficiency of spring wheat in the semi-arid Canadian prairies: Effect of legume green manure, type of spring wheat, and cropping frequency

Kröbel, R., Lemke, R., Campbell, C. A., Zentner, R., McConkey, B., Steppuhn, H., De Jong, R. and Wang, H. 2014. Water use efficiency of spring wheat in the semi-arid Canadian prairies: Effect of legume green manure, type of spring wheat, and cropping frequency. Can. J. Soil Sci. 94: 223–235. In the semi-arid Canadian prairie, water is the main determinant of crop production; thus its efficient use is of major agronomic interest. Previous research in this region has demonstrated that the most meaningful way to measure water use efficiency (WUE) is to use either precipitation use efficiency (PUE) or a modified WUE that accounts for the inefficient use of water in cropping systems that include summer fallow. In this paper, we use these efficiency measures to determine how cropping frequency, inclusion of a legume green manure, and the type of spring wheat [high-yielding Canada Prairie Spring (CPS) vs. Canada Western Red Spring (CWRS)] influence WUE using 25 yr of data (1987–2011) from the “New Rotation” experiment conducted at Swift Current, Saskatchewan. This is a well-fertilized study that uses minimum and no-tillage techniques and snow management to enhance soil water capture. We compare these results to those from a 39-yr “Old Rotation” experiment, also at Swift Current, which uses conventional tillage management. Our results confirmed the positive effect on WUE of cropping intensity, and of CPS wheat compared with CWRS wheat, while demonstrating the negative effect on WUE of a green manure crop in wheat-based rotations in semiarid conditions. Furthermore, we identified a likely advantage of using reduced tillage coupled with water conserving snow management techniques for enhancing the efficiency of water use.

Effect of N, P and cropping frequency on nitrogen use efficiencies of spring wheat in the Canadian semi-arid prairie

Kröbel, R., Campbell, C. A., Zentner, R. P., Lemke, R., Desjardins, R. L. and Karimi-Zindashty, Y. 2012. Effect of N, P and cropping frequency on nitrogen use efficiencies of spring wheat in the Canadian semi-arid prairie. Can. J. Plant Sci. 92: 141–154. Knowledge of nitrogen use efficiency (NUE) is useful for determining fertilizer requirements. We used balance and difference methods to determine the effect of N and P fertilizer on nitrogen use efficiencies for continuous wheat (Triticum aestivum L.) (Cont W) and fallow-wheat-wheat (F-W-W) in a 39-yr crop rotation study conducted on a Brown Chernozem at Swift Current in semi-arid southwestern Saskatchewan. In the balance method, NUE was estimated as yield (Y), or grain N content (GN), divided by either fertilizer N (FN), or FN+soil test N (SN), or FN+SN+growing season net N mineralization (Nmin). Most reasonable results [calculating NUE as either (Y or GN)/(FN+SN+Nmin)] were unaffected by fertilizer or rotation and averaged 10.9 kg grain kg−1available N and 0.3 kg grain N kg−1available N, respectively, for the different fertilizer treatments of Cont W and F-W-W. Using the difference method, where check values are deducted from treatment values in the numerator, Cont W had greater NUE than F-W-W (roughly 2:1). Variations in NUE were not easily explained in the rotation experiment because of the confounding effect of concurrent increases in available moisture and FN availability in the last decade. However, results from a semi-controlled lysimeter experiment at Swift Current showed that irrigation increased NUE, while increasing FN decreased NUE curvilinearly. Of the methods used to assess NUE, the simplest (Y/FN) was the least accurate. However, data needed for more accurate estimates are less likely to be available to the farming community.