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The many benefits of fertilizer efficiency with Inside View of October 2015

October 2015 – After the last “Inside View” editorial on fertilizer efficiency, a colleague in the supply industry wrote to me saying that “it is easy to put a smorgasbord [of nutrients] in front of the plants every day and let them choose what they want, instead of selectively giving them a balanced diet that doesn’t allow for overconsumption of certain fertilizers that outcompete others.”

Part of the reason he believes this is the case is an apparent lack of interest or desire to apply ourselves to this topic. Perhaps one of the side effects of the Green Revolution is that fertilizers have been too cheap for too long!

As a grower you may have been subject over the past few years to the strong fluctuations in fertilizer pricing that have been passed on to you by your suppliers. These variabilities have been due to a number of reasons, including production shortages and currency inequalities (the recent plummet of the loonie won’t really help matters for the near future!). Not only do these issues cause you pain, they also mean that our suppliers have to work hard to plan maybe years ahead in order to ensure they have stock available for you at a reasonable price.

If you’ve not been tuned in to the phosphorus story, here’s a quick synopsis:

“Food production requires application of fertilizers containing phosphorus, nitrogen and potassium [on agricultural fields] in order to sustain crop yields. However, modern agriculture is dependent on phosphorus derived from phosphate rock, which is a non-renewable resource and current global reserves may be depleted in 50 to 100 years. While phosphorus demand is projected to increase, the expected global peak in phosphorus production is predicted to occur around 2030. The exact timing of peak phosphorus production might be disputed, however it is widely acknowledged within the fertilizer industry that the quality of remaining phosphate rock is decreasing and production costs are increasing.”1

Greenhouse vegetable growers have always taken frequent hydroponic samples to check irrigation fertilizer levels. This is easy, cheap and quick to do, with results reported in ways that growers generally find easy to interpret and apply.

But it’s not the whole picture of crop nutrition. So, in 2014 about a dozen growers and an industry consultant in B.C. embarked on applying a specific fertilizer program and using plant sap analysis to see if they could improve fertilizer use efficiency. Likewise, growers in Ontario were also investigating it.

According to industry sources, “the results have been the lower use of potassium and other macronutrients, and an increase in the use of micronutrients (which improves the efficiency of macros). Some of the numbers in fertilizer savings have been huge.”

Reduced use of potassium also helped suppliers better manage a production shortage in Chile due to an earthquake. Growers also reported other benefits, including:

• (Perceived) Healthier crop.
• Higher production (although this may be also be due to weather effects).
• Improved disease resistance.

For sure, this is only one year of study, and there are probably other reasons for some of these benefits. But even if only half of the fertilizer savings are a direct result of this program, it is worth doing. Financial benefits aside, it is surely a more responsible way to grow. (Consider the earlier phosphorus story!)

As well as carefully monitoring fertilizer inputs (which, to be fair, most responsible growers do anyway), limiting (un-used) fertilizer waste in irrigation runoff is equally important. To that end, studies in the Netherlands are looking at using flocculating techniques to recover fertilizers that have left the greenhouse and before they enter off-site surface water.

Studies in the U.K. some 30 years ago showed about 40 per cent of the fertilizer applied to a greenhouse vegetable crop simply went down the drain. That’s clearly an over-estimate in today’s re-circulating systems, but there is still some potential to reduce this waste to zero.

1 Cordell, Dana, et al, (2009), “The story of phosphorus: Global food security and food for thought.” Global Environmental Change, Vol. 19, no 2, 292-305.

Gary Jones is co-chair of horticulture at Kwantlen Polytechnic University, Langley, B.C. He serves on several industry committees and welcomes comments at Gary.Jones@kpu.ca.