The results of this study indicate that juncea canola can be considered as an alternate oilseed crop that is adapted to the semiarid areas of the northern Great Plains where high temperature and drought stresses often limit the productivity of conventional napus and rapa canola species.
Brassica juncea canola is a relatively new oilseed species that is developed from Brassica juncea mustard with its oil and meal quality equivalent to conventional canola species. Some agronomic
research projects have been conducted in western Canada in the past, but information on the yield responses to diverse environmental conditions in the different agroecological regions or soil-climatic zones in western Canada is still lacking. Also, nitrogen (N) accounts for the largest energy input in oilseed production, but little is known about how this juncea canola would respond to N fertilization under various growing conditions. Yield potential, response to stress, yield stability, and N input and use efficiency are some of the key issues about this species. Knowing these characteristics will help producers to improve crop adaptability and N use efficiency and thus minimize production costs and environmental impacts. Also, information on the phenological characteristics of this crop under diverse environments will allow the crop to be better adapted to target production areas in western Canada.
The objectives of this project were:
- To determine the responses of the juncea canola to various soil-climatic conditions in comparison with napus canola, rapa canola, juncea mustard, and Sinapis alba mustard.
- To determine N use efficiency and N uptake of juncea canola in comparison with napus and rapa canola species and alba and juncea mustard under varying soil and climatic conditions with low-, average-, and high-yielding potentials.
- To evaluate the difference in the degree of resistance to seed and pod shattering among five canola/mustard species/cultivars under straight combine versus swathing management regimes.
Two field experiments were conducted at four sites (Melfort, Scott, Saskatoon, and Swift Current), in Saskatchewan over the course of 2003-2006 growing seasons.
Experiment 1 had two objectives:
- Yield potential and response to environmental conditions of Brassica juncea canola in different soil-climatic zones
- Nitrogen use efficiency and N uptake of juncea canola under diverse environments.
Experiment 2 evaluated five canola/mustard species/cultivars under straight combine versus swathing management for seed shattering.
In Experiment 1, the five oilseed species/cultivars were grown under various N fertilizer rates (0, 25, 50, 100, 150, 200, and 250 kg N ha-1) at four sites from 2003 to 2005. On average, flowering began 40 days after seeding (DAS) for alba mustard and rapa canola (earliest), 49 DAS for napus canola (latest), and 44 DAS for juncea canola (intermediate). Flowering duration was longest for juncea canola (30 days) and shortest for napus canola (22 days). The napus canola and juncea mustard produced higher (1684 kg ha-1) seed yields than the three other oilseeds
(1303 kg ha-1 on average). For all oilseed species, the seed yield was highly responsive to N fertilizer rates from zero to about 100 kg N ha-1, and thereafter, the rate of yield responses declined. The amount of N fertilizer required to achieve the maximum seed yield was 106 kg N ha-1 for rapa canola, 135 kg N ha-1 for alba mustard and napus canola, and 162 kg N ha-1 for the two juncea spp.
Overall, juncea canola had lower seed yield than more popular hybrid napus canola, and the yield stability of juncea canola was lowest among the five oilseed species when examined across diverse environments. Earlier flowering, longer flowering duration, and greater tolerance to drought stress exhibited by juncea canola make the crop best adapted to the drier areas of the northern Great Plains. The improvement of seed yield and yield stability is the key to potentially adapt this new oilseed species to a wider range of environmental conditions.
Nitrogen use efficiency (NUE; defined as seed yield produced per unit of N supply), N fertilizer use efficiency (NFUE; defined as seed yield produced per unit of fertilizer N), and crop N uptake were determined for the five oilseed crops/species. At sites with low soil N supply or low rainfall, alba mustard, juncea canola, and rapa canola had lower NUE and NFUE than juncea mustard and napus canola. At sites with high soil N supply or rainfall, napus canola had the greatest NUE and was the most sensitive to the gradient of productivity among the five oilseeds. All oilseed species responded to N fertilizer rates in a similar manner; both NUE and NFUE decreased as N fertilizer rate increased. The minimum NUE and NFUE were obtained with N fertilizer rate greater than 150 kg N ha-1.
At sites with low soil N supply or rainfall, alba mustard had the least NUE or NFUE response to increasing N fertilizer rates and napus canola the greatest. At sites with high soil N supply or rainfall, juncea mustard had the least NUE and NFUE response to increasing N fertilizer rates and rapa canola the greatest. On average, seed N uptake was greatest for juncea canola and juncea mustard and least for alba and rapa canola. The five oilseed species had similar response patterns of seed N uptake to N fertilizer rates, while the magnitude of response varied among species. Improving NUE in oilseed production systems requires optimizing rates of N fertilizer which vary depending on environmental conditions, and soil N supply and rainfall during the critical growth period of the oilseed crops play an important role in affecting NUE.
In Experiment 2, under adverse harvesting conditions, all oilseed species/cultivars tested in the study had seed yield losses ranging from 2.4 to 7.7%, which was significantly higher than when harvesting conditions were favourable. Under high shattering conditions, there were large differences in yield loss among species during straight combining. Brassica juncea mustard had the greatest seed yield and also had the greatest percent yield loss. Brassica rapa canola had the lowest seed yield with lowest percent yield loss. It appears that resistance to shattering is more inherent to oilseed species. To minimize harvest loss of seed yield in crucifer species, one should consider selecting species and cultivars with pods having favourable morphological and physiological traits for pod shattering resistance in combination with the adoption of straight combining practices.
The results of this study indicate that juncea canola can be considered as an alternate oilseed crop that is adapted to the semiarid areas of the northern Great Plains where high temperature and drought stresses often limit the productivity of conventional napus and rapa canola species. It appears that the juncea canola cultivars have improved some key phenological traits such as earlier flowering, longer duration of flowering and maturity, and improved drought tolerance during the reproductive growth period. These improved phenological characteristics help improve the adaptation of this new oilseed species to the drought-prone regions of the northern Great Plains.
However, the current cultivars of juncea canola do not have the yield potential of the more popular hybrid cultivars of napus canola, and the yield stability juncea canola is lower than other oilseed species/cultivars when tested across diverse environments. Longer maturity of juncea canola crop may be a concern in cooler and short-season areas of the northern Great Plains. Compared to the high-yielding napus canola and juncea mustard, the seed yield of juncea canola had a weaker response to increased rates of N fertilizer, suggesting that N use efficiency of juncea canola is low. Further genetic enhancement in conjunction with improved management practices may be able to narrow the gaps in yield potential and N use efficiency between juncea canola and napus canola. There exist needs to determine if crop management practices such as altering seeding date or adjusting seeding rates would increase seed yield, improve yield stability and N fertilizer use efficiency for juncea canola. Further investigation of these factors on juncea canola is warranted.