Choice of Crop Stubble and Grain Yield

By Yantai Gan, Research Scientist

Semiarid Prairie Agricultural Research Centre

Agriculture and Agri-Food Canada

Swift Current

Phone: (306)778-7200. E-mail: gan@em.agr.ca

Choice of Stubble

In recent years, many producers in the Brown and Dark Brown soil zones have been diversifying their cropping systems by including non-cereal crops such as canola, field pea, lentil, and/or chickpea in the system. The inclusion of those alternative crops in the cropping system provides producers with options to grow their crops on different types of stubble. Crops perform much better on one type of stubble than another type. Thus, the wise selection of crop stubble can maximize crop yield.

Research Experiment

A field study was conducted on a loam soil at Swift Current and a clay soil at Stewart Valley, Saskatchewan, from 1996 to 1999. Field pea, lentil, chickpea, mustard and wheat were grown in the experiment. The following year, canola and spring wheat was re-cropped on the five different crop stubbles. Nitrogen fertilizer was applied to the re-cropped canola and wheat with the total amount of soil available N equal to 65 to 70 kg N ha^-1, based on soil test. Nitrogen credits from the pulse stubble were taken into account in the fertilizer calculation.

Soil Water at Seeding

Soil water was measured to the 120 cm (4-feet) soil depth in stubble fields immediately before seeding. Large differences were found among the five types of stubble in conserving soil water (Table 1). Pea and lentil stubbles conserved about 10% more available water than wheat stubble. The soil available water in chickpea stubble was less than those conserved in pea or lentil stubbles, but was equivalent to that conserved in wheat stubble. Mustard stubble conserved the least soil water. The status of soil water at seeding time was closely related to the water-use characteristics of the previous crops. Pea and lentil used much less water than the other crops during the previous growing season, and thus a large portion of soil water was conserved below the 60-cm (2-feet) soil depth.

Table 1. Soil Available Water at planting in the following spring, measured in the five different stubble fields at Swift Current and Stewart Valley, from 1997 to 1999.

Soil Residual N at Seeding When measured on the loam soil at Swift Current, pea and lentil stubbles had 17 to 23% more soil residual N in the 120-cm soil depth than wheat stubble (Table 2). On clay soil at Stewart Valley, the residual N conserved by pea and lentil stubbles was even greater; over 70% more than that conserved by wheat stubble. Chickpea conserved less soil residual N than pea or lentil, but it was significantly higher than those conserved by wheat or mustard. Those observations were similar across all the three years.

Table 2. Soil residual N at Planting in the following spring, measured in the five different stubbled fields on loam (at Swift Current) and clay soil (at Stewart Valley), from 1997 to 1999.

^† Fallow check data presented here for reference only.

We used the N equivalent information in fertilization management for crops grown on the different stubbles in the following years. For canola and wheat re-cropping, fertilizer N application was adjusted to provide an equal amount of soil available N, targeting an equal yield goal on all crop stubbles. In this manner, crops grown on the pea stubble received an average of 20 kg N ha^-1 less than crops grown on wheat stubble. Crops grown on the lentil and chickpea stubbles received 10-15 kg N ha^-1 less than those grown on wheat stubble. This size of N contribution from pulses was larger than expected. It appears that N contributions from the pulse crops, especially pea and lentil, have been underestimated by not accounting for conserved N below the 60-cm soil depth.

Grain Yield of the Following Crops

The type of crop stubble had significant influences on canola and wheat grain yields (Table 3). Averaged over six site-years (i.e., 1997, 1998, and 1999 at Swift Current and Stewart Valley), canola grown on pea or lentil stubble produced 20 to 40% higher seed yield than canola grown on wheat or mustard stubble. Canola grown on chickpea stubble produced 5% higher seed yield than those grown on wheat or mustard stubble. The yield patterns were somewhat similar to those with soil available water and residual N as discussed above. Great differences were found when wheat was grown on those five different stubbles. Wheat grown on mustard stubble produced 17% more grain than wheat grown on its own stubble. Three pulse stubbles (chickpea, lentil, and pea) resulted in significant increases in wheat grain yield (25 to 30%), as compared to wheat stubble. Thus, wheat stubble provided the least benefits to re-cropped wheat, while pea and lentil stubbles were the best for wheat to follow. As expected, wheat grown on summer fallow had the highest grain yield, which was over 50% more than wheat grown on its own stubble, and was 16% more than wheat grown on pea or lentil stubble.

Table 3. Grain yields of canola and hard red spring wheat grown on the five different crop stubbles at southwestern Saskatchewan, from 1997 to 1999.

Yield values followed by the same letter within a column were not statistically significant (P < 0.05).

&#8224; Wheat was also grown on replicated, non-randomized fallow check. These data were not included in the statistical analyses but are provided here for comparison purposes.

Conclusion

Canola and hard red spring wheat grain yields can be significantly improved by growing either crop on stubble other than its own stubble. Pea and lentil stubbles boosted canola seed yield by over 20%, and increased wheat grain yield by around 30%. Chickpea stubble functioned similarly to mustard stubble in terms of water and nutrient conservation, and it is better to grow wheat than canola on chickpea stubble. Stubble also affects seed/grain quality. The seed size of both canola and wheat was significantly increased when those crops were grown on pea and lentil stubbles. The yield and quality benefits associated with pulse stubbles are in addition to nitrogen credit, since N benefits had been taken into account in fertilizer management.