DIFFERENT BRASSICACEAE SPECIES IN ROTATION WITH PULSE CROPS AND WHEAT: EFFECTS ON BIOLOGICAL NITROGEN FIXATION, SELECTED SOIL PROPERTIES AND WHEAT PRODUCTIVITY
Date
2025-01-06
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Degree Level
Doctoral
Abstract
Brassicaceae crops produce glucosinolate (GLS)-degradation products with antimicrobial properties. Amounts and compositions of GLS vary among Brassicaceae species. Considering that biological nitrogen fixation (BNF) is microbially mediated, different Brassicaceae species may affect BNF in rotational pulse crops differently. To improve cropping system sustainability, diversifying rotations with lesser-grown crops is essential. Although previous studies have focused on N benefits of pulse crops, the impact of Brassicaceae crops on BNF in subsequent pulse crops and overall crop performance remains unclear. A 4-year field study was conducted at three test sites (Swift Current and Scott in SK, and Brooks in AB) to evaluate the effect of different Brassicaceae crops [Argentine canola (Brassica napus L.), camelina (Camelina sativa L. Crantz), industrial mustard (Brassica carinata L.), oriental mustard (Brassica juncea L.) and yellow mustard (Sinapis alba L.)] on BNF of field pea (Pisum sativum L.) and lentil (Lens culinaris Medikus), soil properties and productivity of wheat grown as the fourth crop in the cycle. Overall, the percentage of N derived from atmosphere (%Ndfa) for field pea grown after Argentine canola was 5.3-34.6 % higher than the average of other Brassicaceae crops at all test sites. The increased nifH gene concentration and root nodule dry weight in field pea on Argentine canola stubble may contribute to enhanced BNF. In contrast, BNF in lentil was not affected by the preceding Brassicaceae crop species at all test sites, except at Brooks. Lentil grown on Argentine canola stubble showed 17.9 % higher %Ndfa and 26.6 % higher fixed N content than other Brassicaceae crops at Brooks, potentially attributable to higher root nodule dry weights. Thus, the impact of Brassicaceae crops on BNF of pulse crops may vary depending on the pulse crop species and test site. In addition, a controlled environment study with field pea showed that high GLS content (6.49 µmol g-1 of tissue) suppressed effective root nodulation by 14.6 % and soil nitrification by 16.2 % compared to zero GLS. Negligible GLS content in Argentine canola residues (0.02 µmol g-1 of tissue) was likely non-suppressive for beneficial interactions with diazotrophs, leading to increased BNF in pulse crops compared to other Brassicaceae crop residues. The field study further revealed that Brassicaceae and pulse crops in wheat-based crop sequences did not influence the selected soil properties within the 4-yr time frame. On average, crop sequences with Argentine canola consistently had higher amounts of light fraction organic matter than other Brassicaceae crops. Nonetheless, crop sequences with Brassicaceae and pulse crops increased seed yield of subsequent wheat by 57 % and 1000-seed weight by 7.2-9.7 % compared to continuous wheat at test sites in the Brown soil zone. Argentine canola followed by either field pea or lentil increased subsequent wheat production by over 30 % compared to other Brassicaceae-pulse combinations at Swift Current. Overall, the study suggests that the inclusion of Brassicaceae oilseed and pulse crops in wheat rotations offers advantages over continuous wheat, particularly in the Brown soil zone. Moreover, Argentine canola appears to provide more benefits than other Brassicaceae oilseed crops, potentially enhancing cropping system performance.
Description
Keywords
Glucosinolate, Isothiocyanate, wheat-based rotations, soil properties, crop yield
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Soil Science
Program
Soil Science