Objetives
- To determine the impact of tillage system on phosphorus (P) fertilizer response of canola and wheat.
- To determine the yield response of flax to P fertilization application, as influenced by preceding crop and tillage system and level of P fertilization in preceding crop.
- To determine the effect of tillage system, preceding crop and P fertilizer management on Cd content of flax.
- To determine the degree of mycorrhizal activity in flax, as affected by preceding crop and tillage system.
- To determine the early season accumulation of P by flax as influenced by preceding crop and tillage system.
Project Description
When canola seed yield was averaged over the three years of the study, there was an increase in canola yield with P application at the Research Centre site, but no effect of tillage and no tillage by P interaction. However, yields were numerically higher under conventional till (CT) as compared to no-till (NT), primarily due to poor performance of NT in the cold, wet, late seasons of 1999 and 2000. At the Manitoba Zero Tillage Research Association (MZTRF), canola seed yield was increased by P application and seed yield was higher under CT than NT. There was also a P by tillage interaction, with seed yield increasing more with P application under CT than under NT. It therefore does not appear that differences in seed yield between NT and CT were caused by restricted P availability under NT.
The major factor influencing flax yield was the preceding crop, with seed yield being much higher after wheat than after canola. The effect was evident from crop emergence, through early season growth, to final straw and seed yield. Seed yield was higher when flax was grown after wheat rather than canola at both locations. When averaged over the three years of the study, seed yield was 9.8% higher after wheat than after canola at the Research Centre site and 22% higher after wheat than after canola at the MZTRF site. The effect may be due to a number of factors, including some degree of allelopathy from canola residue, early season competition from volunteer canola plants or restriction in mycorrhizal colonization after canola.
Effect of P fertilization on flax varied from location to location and year to year but generally had little impact on final flax yield. Seed yield tended to decrease with P application to flax under NT at the Research Centre location in 2000, possibly due to seedling damage. At the Research Centre in 2001, seed yield of flax grown after wheat increased slightly and grown after canola decreased slightly when P was added to flax. In 2002, on the Research Center site, seed yield increased slightly with P application to the flax. Over the three years of the study, there was a tendency for seed yields to be higher when P, although the difference was small. At the MZTRA, there was no significant difference in seed yield when P was applied to the flax in any year of the study or when the results were averaged over the three study years. Seed yield also tended to be higher at the MZTRF when flax was grown under conventional tillage rather than no-till. The effects of residual P on seed yield were not consistent. In 2000, at the MZTRA, P fertilization of the preceding crop led to higher flax seed yield the following year, with the effect being greater when wheat was the preceding crop as compared to canola. In 2001, residual P did not increase flax seed yield. In 2002, at the MZTRF, flax seed increased with residual P under no-till and decreased or remained constant with residual P under CT. Over the three study years, there was no significant effect of residual P on seed yield of flax at the Research Centre site. At the MZTRF, there was a tendency for seed yield to decrease with residual P when canola was the preceding crop and P fertilizer was applied.
In both years of the study, preceding crop had a dominating effect on mycorrhizal association. Mycorrhizal association in flax at five weeks was higher when the flax was grown after the mycorrhizal crop, wheat, than after the non-mycorrhizal crop, canola. Association was also generally increased by using reduced tillage as compared to conventional tillage. Mycorrhizal association and biomass yield at five weeks tended to respond similarly to preceding crop and tillage system at both locations. The effect of P application to either the receding crop or the flax was smaller than the effect of preceding crop or tillage.
Concentration of cadmium (Cd) in flax seed was higher after canola than wheat and was increased by application of P to the previous crop. At the MZTRA, side-banded P increased seed Cd concentration, particularly under NT in canola, but there was no response at the Research Centre. Tillage system did not consistently influence Cd concentration in the seed. Part of the effect on Cd concentration in the seed may relate to dilution/concentration changes.
Phosphorus nutrition of flax can be influenced by tillage system, preceding crop, residual P from fertilization of receding crops and by side-banded P application in the flax. Therefore, it may be possible to select different P management strategies to optimize flax P nutrition and seed yield, depending on the cropping system and crop rotation used and the equipment available. The overall benefit from either applying P fertilizer to the flax crop or increasing P application in the preceding crop to benefit the following flax crop was minimal. The P status of these soils was low to moderate and P fertilizer responses occurred in other crops. Phosphorus fertilization of flax may be more beneficial on soils where P supply is extremely depleted. However, with moderate deficiencies, the benefit is likely to be low. A phosphorus management strategy to maintain P through the rotation by targeting applications to more responsive crops would possibly be more cost-effective than application of P to flax. If soil P levels are not depleted, increasing the rate of application of P to preceding crops will likely not improve the yield of the following flax crop.
Generally, production of flax after canola appears to be a poor option. The negative effect of canola as a preceding crop was present from emergence through to final seed yield. Poor performance of flax after canola may have been due to effects on mycorrhizal association and P nutrition, or possibly due to allelopathic effects of the canola residue. However, the impact of extremely competitive volunteer canola competing with falx in the early stages of crop growth may also be important.
