Question: Is seed-placement an effective method of applying micronutrients?
Answer: No, except for manganese.
Rationale: Work initiated by Western Co-operative Fertilizers Limited in 1995 on a number of sites in western Canada has been designed to address the issue of seed-placement versus broadcast and incorporation and foliar application of micronutrient products, especially copper.
Three products were seed-placed at a site in Lacombe, Alberta on a soil containing 0.35 ppm DTPA-extractable copper/acre, namely, an oxysulphate, a granular chelated (EDTA) and a sulphate product containing copper. Seed-placement of 2 lb Cu/acre was repeated on the same plots every year for four years (1995-1998) and was compared to a 4 lb Cu/acre broadcast and incorporation application (Figure 1). Significant responses (P<0.05 and P<0.01) to copper applied by broadcast and incorporation were obtained every year. Seed-placement of the chelated and sulphate products resulted in significant (P<0.05) responses in 1998 only, however, broadcast and incorporation of copper resulted in maximum yield every year. The experiment was continued in 1999, however, no further copper applications were employed in an attempt to assess the residual effect of the applied treatments.
Final yields of wheat grown on these residual copper plots (Figure 2) are shown for all copper rates employed in this experiment. Broadcast and incorporation of 4 lb Cu/acre produced the highest yield. Although significant responses were indeed obtained with annual seed-placed rates of 3.6 lb Cu/acre, this rate defeats the purpose in attempting to effectively and economically correct a copper deficiency, since a single broadcast and incorporation of 4 lb Cu/acre has an effective residual effect. Conversely, broadcast and incorporation of less than 3.6 lb Cu/acre are equally ineffective to a seed-placement. However, seed-placement of 1.8 lb Cu/acre of either a chelated or a sulphate product did produce a significant yield increase and conceivably can be considered an alternative for direct seeding recognizing, of course, that it will not lead to a maximum yield.
Figure 1. Yield responses to annual application of seed-placed and broadcast and incorporated copper products at Lacombe, Alberta.
Figure 2. Yield responses of wheat grown on residual treatments of seed-placed and broadcast and incorporated copper products at Lacombe, Alberta in 1999.
Question: Is foliar application an effective method of applying micronutrients?
Answer: Yes.
Rationale: Foliar application of copper at 0.2 lb Cu/acre proved to be extremely effective providing the soil was not severely deficient in copper (Figures 3 and 4). However, when a soil is severely deficient a foliar application may not be sufficient to alleviate a copper deficiency (Figure 5). In cases of a severe copper deficiency the producer should be seeking a long-term economic solution and even be willing to sacrifice a direct seeding operation in order to correct a micronutrient problem. Broadcast and incorporation of a copper sulphate product is the only practical solution.
Figure 3. Comparison of foliar to broadcast and incorporated application of copper.
Figure 4. Application of foliar copper alleviates copper deficiency as a result of the inability of seed-placed copper to correct the deficiency.
Figure 5. Application of foliar copper to a severely deficient copper crop cannot completely alleviate copper deficiency.
An alternative to this practice could be a combination of seed-placement of either a chelated or a sulphate product with a foliar application of an appropriate copper product to achieve optimum yields in at least the first two years of the program. However, this practice may not always provide the best economic solution.
Question: Why is seed-placement an ineffective method of applying micronutrients?
Answer: A number of reasons are being contemplated for the inability of seed-placed copper products to provide maximum or consistent yields increases. For example, physical distribution of 1 to 1.5 lb of Cu/acre in a band leads to fertilizer granules being at great distances from each other and inability of roots to access copper. Hot bands or a P X Cu interaction are also contemplated but none of these mechanisms have ever been proven as being responsible.
Question: Are there any alternative practices or seed-placed products being tested?
Answer: In a series of experiments conducted in 2000, a number of products and practices were tested to assess the effectiveness on seed-placed products. Seed-placement of four products, two available in the market and two experimental, was compared to broadcast and incorporation of 5 lb copper sulphate-Cu/acre at five sites. At another three sites, copper as copper sulphate was either broadcast at 5 and 10 lb Cu/acre without incorporation or seed-placed at 1 lb Cu/acre or was applied as foliar at 0.2 lb Cu/acre to assess the feasibility of using this methods of placement in direct-seeded systems. All sites were selected to contain "marginal" levels of Cu, i.e., between 0.4 and 0.8 ppm. Responses were obtained in two sites only.
Seed-placement of Cu was ineffective in alleviating mild Cu deficiency (Figure 6). Broadcast of copper sulphate without incorporation or seed-placement was not effective in alleviating mild copper deficiency, however, foliar application was effective (Figure 7).
Figure 6. Seed-placed Cu does not produce a significant yield increase on a "marginally" deficient soil in Manitoba (Westco unpublished data).
Figure 7. Broadcast Cu without incorporation or seed-placed Cu does not produce a significant yield increase on a "marginally" deficient soil in Saskatchewan (Westco unpublished data).