Template:Chapter 4.17
4.17 - Microdosing of synthetic fertilizers
Dylan P. Harding, University of Guelph, Canada
Suggested citation for this chapter.
Harding,DP. (2022) Microdosing of synthetic fertilizers. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.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 “micro-dosing” has been investigated as a method of maximizing the return on fertilizer investment by maximizing crop uptake.
In the practice of micro-dosing, 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 micro-dosing 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 to 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 onto corn, nitrogen uptake efficiency did not significantly vary between broadcast and seed-placed application (Rees et al., 1997). It should be noted however the 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 micro-dosing techniques with interventions to improve nutrient retention such as adding manure (Ncube, Dimes, Twomlow, Mupangwa, & Giller, 2007).
It should be noted that micro-dose 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 the comparison of these two methods on pearl millet in Sadoré, Niger, it was found that the yields achieved with a micro-dose 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 micro-dose 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 micro-dosing study performed over 4 field seasons on pearl millet in Mali, Burkino 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 micro-dose yields realized in this study were lower than those associated with higher doses of broadcast fertilizer (Bagayoko et al., 2011), micro-dosing 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 micro-dosing 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, was that the value to cost ratio (yield increase per unit of expenditure) of fertilizer investment increased by up to 70% when micro-dosing was employed compared to broadcasting (Muehlig-Versen et al., 2003). Highly positive value to cost ratios have also been realized in the comparison of micro-dose fertilization to unfertilized controls in multiple trials, especially for fertilizer doses of under 1 gram per hill (Aune et al., 2007; Ousman & Aune, 2011).
Micro-dose 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 micro-dose application to millet (variety is unclear) was investigated by Hayashi et al. (2008). 6 g micro-doses of 15-15-15 fertilizer were employed in this study. It was shown that although yields were maximized when fertilizer was applied at planting time, yield improvement in comparison to unfertilized crops could be realized even 45 days after sowing (Hayashi et al., 2008).
Other Challenges
It should be kept in mind that fertilizer micro-dosing will only be effective if nutrients that would otherwise be limiting factors on the growth of a plant are applied, 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 and this 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 in moisture limiting conditions (Muehlig-Versen et al., 2003). In situations where limited moisture at planting time is a reality, fertilizer should be placed near to the seed but not in direct contact with it.
Along with the different materials gloves are made of, there are also different arm lengths. Some gloves are cut off just in front or around the wrist. While others can be up to and over the elbow and everywhere in between (Melco, 2016). The benefits of the shorter gloves is comfort, no bunching around wrist or elbow, and they can be quickly put on or removed. The benefits of the long gloves are more protection, the entire forearm will be covered. All the while there is less of a chance of getting debris in their gloves because the opening is farther away from what you are working with. Farmers can also work in deeper water or mud with the long rubber gloves without getting your hands wet.
Picture Based Lesson to Train Farmers
For the South Asian version (pictures only, text for you to insert), click this link for lesson 5.17:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.17_south_asian.pdf
For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 5.17:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.17e.s.a.pdf
For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 5.17:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.17subsaharan_africa_carribean.pdf
For the Latin-America version (pictures only, text for you to insert), click this link for lesson 5.17:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.17latin_america.pdf
For North Africa And Middle East version (pictures only, text for you to insert), click this link for lesson Chapter 5. 4.14:http://www.sakbooks.com/uploads/8/1/5/7/81574912/4.14n._africa_middleeast.pdf
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
[ICRISAT Micro-dosing Manual: http://www.icrisat.org/impacts/impact-stories/icrisat-is-fertilizer-microdosing.pdf]
[ICRISAT Micro-dosing Video: http://www.youtube.com/watch?v=c4-AB1jg3Sg]
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