Inclusion of alternative crops such as pea, lentil, chickpea, and canola/mustard in cropping systems provides producers with options to grow cereal crops on different types of stubbles the following years. Fields of different types of stubbles may have been conditioned with different levels of soil moisture, nutrients, and other residual elements. Therefore, growing cereal crops in right crop sequences will allow the crops to best take the stubble advantages and thus to maximize their yields and protein.
A field experiment was conducted at the Agriculture and Agri-Food Canada's Research Centre in Swift Current to determine performance of amber durum grown on different types of crop stubbles or in different crop sequences from 1996 to 2000. Three pulse crops (chickpea, yellow pea, and lentil), one oilseed (oriental mustard), and one cereal (hard red spring wheat) were grown as the first year crops. In the following year (year 2), a common set of crops (i.e., wheat, an oilseed, and a pulse crop) were grown on the five previous crop stubbles. In the 3rd year of the crop sequences, Kyle amber durum was uniformly grown on all 15 combinations of previous crop types (i.e., five crop types from the 1st year x three crop types from the 2nd year). Each phase of the crop sequences was repeated for three cycles during the period from 1996 to 2000. The final cycle was finished in 2000.
Averaged over the five site-years, the Kyle durum seeded in the pulse-pulse-durum crop sequences produced the highest grain yield (48 bu/ac), followed by durum grown in the pulse-canola-durum (47 bu/ac) and mustard-pea-durum (47 bu/ac). The durum grown in the wheat-wheat-durum sequence produced the lowest grain yield (39 bu/ac), which was 19% lower than from the pulse-pulse-durum sequence and 17% lower than from the pulse-canola-durum sequence. It is apparent that the previous two years of pulse crops, and the pulse-oilseed or oilseed-pulse crop sequences provided the durum crop with significant rotational benefits. The increased durum yields in these crop sequences may be attributable to the slow-release of symbiotic soil residual N contributed by the previous pulse crops, coupled with the increased soil moisture conserved by the shallow-rooting lentil and pea crops.
Grain protein content of the Kyle durum was highest (>13.8%) when grown in the pulse-pulse-durum, pulse-oilseed-durum, or oilseed-pulse-durum sequences, followed by wheat-pea-durum (13.5%). Durum grain protein was lowest (11.8%) when durum was grown in wheat-wheat-durum, fallow-wheat-durum, or mustard-wheat-durum sequences. Grain protein levels were reduced sharply when durum was grown on 2nd-year wheat stubble, averaging a remarkable
2.7 %-units lower than when durum was grown on lentil or pea stubbles.
Over the five site-years, as durum yields increased from 26 bu/ac to 57 bu/ac, its protein content decreased from 17.8% to 10.2%. Further increases in durum yield (i.e. greater than 57 bu/ac) did not confirm a significant decline in protein content. The degree of the decline in protein with increased yields was stronger for durum grown in the wheat-wheat-durum sequence than when durum was grown in pulse-durum crop sequence.
The timing of nitrogen release from decomposing pulse residuals in association with soil organic matter dynamics may have contributed to the observed greater yield and protein benefits for the durum crops. In the long term, the inclusion of pulse crops in the crop sequence would significantly enhance the soil's nitrogen pool or improve soil nitrogen availability for cereal or canola crops to follow. Aside from the slow nitrogen release from pulse residuals, other factors also may have contributed to these sizeable rotational benefits, which requires further investigation.