Microdosing of Synthetic Fertilizers
4.17 - Microdosing of synthetic fertilizers
Dylan P. Harding, University of Guelph, Canada
Suggested citation for this chapter.
Harding, D.P. (2022) Microdosing of synthetic fertilizers. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. farmpedia.org
Introduction
Soil fertility is often the limiting factor on crop productivity. Where fertilizer is available, yield-maximizing application rates are rarely practical for many small-scale farmers. However, by applying even very small quantities of fertilizer, significant returns can be realized on the investment when soil fertility is extremely lacking. The practice of fertilizer "microdosing" has been investigated as a method of maximizing the return on fertilizer investment by maximizing crop uptake.
In the practice of microdosing, small quantities of synthetic fertilizer are applied to the soil surface directly surrounding individual plants or buried with the seed in "micro-doses" of up to about 6 grams, measured using a beer or Coca-Cola bottle cap. This technique is an alternative to the more commonly practiced broadcast method of fertilizer application, in which fertilizer, or a mixture of fertilizer and seed, is spread over the field. The theory behind microdosing is that low rates of fertilizer can be most efficiently applied by minimizing the distance between the fertilizer and the root system. This is thought to be beneficial for both mobile and immobile nutrients, which can either be lost before they reach the root system (Zhang et al., 2010) or remain fixed in a field area that crop roots will not access in early stages of growth (Eghball & Sander, 1989; Zhang et al., 2010), respectively. Additionally, direct placement of fertilizer near seeds and seedlings has been observed to stimulate early root growth and subsequent nutrient uptake (Zhang et al., 2010).
When a high rate of nitrogen fertilizer in the form of urea (210 kg N/ha) was applied to corn, nitrogen uptake efficiency did not significantly vary between broadcast and seed-placed application (Rees et al., 1997). It should be noted, however, that recovery of applied N was fairly low (<30%) for all trials in this study (Rees et al., 1997). Nitrogen recovery could potentially be improved at lower application rates by combining microdosing techniques with interventions to improve nutrient retention, such as adding manure (Ncube, Dimes, Twomlow, Mupangwa, & Giller, 2007).
It should be noted that microdose fertilizer application is more time consuming than broadcast application. Despite this drawback, enhanced nutrient uptake can justify the increased labour requirement in situations where yield-maximizing fertilizer application is not practical. In a comparison of these two methods on pearl millet in Sadoré, Niger, it was found that the yields achieved with a microdose application of 7 kg P/ha were 88% of those achieved with a 13 kg/ha broadcast application, indicating that comparable yields can be achieved with much less fertilizer using microdose application techniques (Muehlig-Versen, Buerkert, Bationo, & Roemheld, 2003). This study also found phosphorus use efficiency to be increased with seed-placed phosphorus application over broadcast phosphorus application (Muehlig-Versen et al., 2003). In another microdosing study performed over 4 field seasons on pearl millet in Mali, Burkina Faso and Niger, low micro-doses of NPK fertilizers were observed to significantly increase grain and stover yield compared to trials where no fertilizer was applied (Bagayoko et al., 2011). Though the microdose yields realized in this study were lower than those associated with higher doses of broadcast fertilizer (Bagayoko et al., 2011), microdosing was likely more cost effective.
The key lesson to emerge from field trials in Africa using various crops (pearl millet, sorghum, cowpea, groundnut, sesame) is that even very small amounts of fertilizer, where needed, when applied using the microdosing technique, can significantly increase crop yields in nutrient-poor soils (Aune, Doumbia, & Berthe, 2007; Buerkert, Bationo, & Piepho, 2001; Hayashi, Abdoulaye, Gerard, & Bationo, 2008; Ousman & Aune, 2011). Furthermore, and of critical importance to poor farmers, the value-to-cost ratio (yield increase per unit of expenditure) of fertilizer investment increased by up to 70% when microdosing was employed compared to broadcasting (Muehlig-Versen et al., 2003). Highly positive value-to-cost ratios have also been realized in the comparison of microdose fertilization to unfertilized controls in multiple trials, especially for fertilizer doses of under 1 gram per hill (Aune et al., 2007; Ousman & Aune, 2011).
Microdose fertilizer application may not be practical at planting time because of labour constraints, high early-season cost, or fertilizer unavailability. To address this reality, the effect of delayed microdose application to millet was investigated by Hayashi et al. (2008), using 6 g micro-doses of 15-15-15 fertilizer. It was shown that although yields were maximized when fertilizer was applied at planting time, yield improvement in comparison to unfertilized crops could still be realized even 45 days after sowing (Hayashi et al., 2008).
Other Challenges
It should be kept in mind that fertilizer microdosing will only be effective if the nutrients applied are ones that would otherwise be limiting factors on plant growth, so a prior soil nutrient test can be helpful if available. Additionally, synthetic fertilizer must be available to the farmer in some quantity. This technique is more time consuming than broadcast fertilizer application, which may pose a barrier to adoption in some communities. It is not clear that crops requiring high doses of a nutrient (e.g. nitrogen for corn) would significantly benefit from low micro-doses of that nutrient. Finally, it should be noted that germination has been shown to be inhibited by the presence of seed-placed fertilizer, especially under moisture-limiting conditions (Muehlig-Versen et al., 2003). In situations where limited moisture at planting time is a reality, fertilizer should be placed near the seed but not in direct contact with it.
Picture Based Lesson to Train Farmers
South Asian version (pictures only, text for you to insert) — lesson 5.17
East/South Asian version (pictures only, text for you to insert) — lesson 5.17
Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert) — lesson 5.17
Latin America version (pictures only, text for you to insert) — lesson 5.17
North Africa and Middle East version (pictures only, text for you to insert) — lesson 4.14
Source: MN Raizada and LJ Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.
Further Reading and Links for Practical Tips
References
1. Aune, J. B., Doumbia, M., & Berthe, A. (2007). Microfertilizing sorghum and pearl millet in Mali - Agronomic, economic and social feasibility. Outlook on Agriculture, 36(3), 199-203.
2. Bagayoko, M., Maman, N., Pale, S., Sirifi, S., Taonda, S. J. B., Traore, S., & Mason, S. C. (2011). Microdose and N and P fertilizer application rates for pearl millet in West Africa. African Journal of Agricultural Research, 6(5), 1141-1150.
3. Buerkert, A., Bationo, A., & Piepho, H. P. (2001). Efficient phosphorus application strategies for increased crop production in sub-Saharan West Africa. Field Crops Research, 72(1), 1-15. Link
4. Eghball, B., & Sander, D. H. (1989). Distance and distribution effects of phosphorus fertilizer on corn. Soil Science Society of America Journal, 53(1), 282-287.
5. Hayashi, K., Abdoulaye, T., Gerard, B., & Bationo, A. (2008). Evaluation of application timing in fertilizer micro-dosing technology on millet production in Niger, West Africa. Nutrient Cycling in Agroecosystems, 80(3), 257-265. Link
6. Muehlig-Versen, B., Buerkert, A., Bationo, A., & Roemheld, V. (2003). Phosphorus placement on acid arenosols of the West African Sahel. Experimental Agriculture, 39(3), 307-325. Link
7. Ncube, B., Dimes, J. P., Twomlow, S. J., Mupangwa, W., & Giller, K. E. (2007). Raising the productivity of smallholder farms under semi-arid conditions by use of small doses of manure and nitrogen: A case of participatory research. Nutrient Cycling in Agroecosystems, 77(1), 53-67. Link
8. Ousman, A., & Aune, J. B. (2011). Effect of seed priming and micro-dosing of fertilizer on groundnut, sesame and cowpea in western Sudan. Experimental Agriculture, 47(3), 431-443. Link
9. Rees, R. M., Roelcke, M., Li, S. X., Wang, X. Q., Li, S. Q., Stockdale, E. A., et al., & Richter, J. (1997). The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils. Nutrient Cycling in Agroecosystems, 47(1), 81-91.
10. Zhang, F., Shen, J., Zhang, J., Zuo, Y., Li, L., & Chen, X. (2010). Rhizosphere processes and management for improving nutrient use efficiency and crop productivity: Implications for China. In D. L. Sparks (Ed.), Advances in Agronomy (Vol. 107, pp. 1-32).