Nutrients and Energy, Yield and Profit – another view ( note comments on precision farming)

The producer earns a profit when the crop yield realised and price received for the crop exceeds the cost of production.

In agriculture the yield selling price is set by the market and there is also not much the producer can do about the price and cost of conventional production inputs. The ratio between the price received for the outputs produced and the price paid for the inputs used in production has been in a declining trend over the long term, and this is a persisting problem. In other words, the producer earns less on a unit of produce now than in the past.

This decline in the yield to cost ratio has however largely been offset by a long-term upward trend in agricultural productivity. More is now being done with the capital employed and thanks to improvements in technology less labour is required to do so than in the past. To further build on the success achieved in productivity improvement, technology driven enhancements in production efficiency and precision is now the goal for ‘generating’ cost savings to maintain profitability.

This approach cannot be faulted; producers need to continually improve productivity through efficiency and precision, agriculture is after all a business like any other. However, there is one significant difference between agriculture and all other production businesses. In agriculture the soil represents the ‘production machine’ and everything added to it the raw materials. All other mechanical machines are the tools used to keep the production machine operating satisfactorily and for handling the throughput (produce).

Improving raw materials efficiency (4R approach – right source and right rate, applied at the right time and right place) by employing technology allowed precision to maximize throughput (yield) without due consideration of the production machine maintenance requirements leads to a loss in production throughput. An optimised production machine produces more, for longer and more regularly. That is the hallmark of a fertile soil.

How does a fertile soil differ from non-optimised soils?

Fertile soils do not differ much from less fertile soils but do, as a general rule, differ somewhat in many important aspects. To illustrate this point, I looked for a research paper containing a good number of soil tests. The paper I used is by Ferreira et al, 2010* (its choice is random, and of no special significance except that it is freely available on the web). It contains yield data and some soil parameters for 40 different natural pasture sites. This I used to rank the various sites, based on their biomass yield, to inform on the importance of individual soil parameters and to compare the top 10 yielding sites with the remaining 30 worse performing sites.

What I saw from this was that the top 10 yielding sites on average had a:

  1. higher level of organic matter (OM), better water holding capacity(WHC) and more of the measured nutrients, except for K,
  2. lower pH, C:N, C:P and N:P ratio, and a
  3. similar bacterial (FL N-fix) count than the 30 worse performing sites.

I did not see:

  1. a high N availability automatically increasing yield (only four of top 10 yielders were in top 10 N ranking),
  2. any other soil parameter being the key determinant in yield (every other parameter only had a limited number of top 10 yielders in the top 10 individual parameter rankings whether it was OM (4), WHC (5), pH-slightly acidic (1), P (4), K (2), Mg (2), B (3), N-bacteria (4)),
  3. any ratio between individual parameters showing a linear correlation with yield. Seven sites with the highest N:K ratio was amongst the top 10 yielders but the two best yielding sites were not in this group and showed vastly different ratios. The same applied to the P:K ratio but only the second best yielder was included in the group.

What I did note was that:

  1. the top 10 yielding sites (top 25%) produced more than 100% more on average than the bottom 30 sites (75%), and even so if you exclude the 10 worst yielding sites,
  2. there was, on average, only a few percentage points difference between the top 10 yielding sites and the bottom 30 sites for all measured parameters on an individual basis, except for P.
  3. the percentage difference in parameter measures do however become significantly starker (more noticeable) if only a few of the top yielding sites are compared to a same number of bottom worst yielding sites.
  4. the concentration of P is significantly higher in the top 10 yielding sites, roughly three times the average of the remaining sites.

The Ferreira et al, 2010 study suggested that soil fertility can easily be increased by the addition of phosphorus, as P2O5 levels were low in the ecosystem. They recommended the use of a calcium based phosphorus fertiliser as the pH in the ecosystem is also low in general.

Is it as simple as that? Will phosphorus amendment unlock additional fertility when only 11 of the 30 worse performing sites have a lower P value than the worst top 10 yielder? I think not!

Energy improves soil fertility

This is the point I’d like to get to –adding a nutrient or a few nutrients may improve the abiotic environment and help increase crop yield but is generally not sufficient to truly unlock the greater portion of the crop’s yield potential and for ensuring that production remains in the top quartile. That requires an improvement in soil fertility, and soil fertility is simply more than nutrient availability.

Optimal yield is the result of a properly functioning agri-ecosystem. If the other system components are not supportive of the increase in a nutrient’s availability, then limited benefit (yield response) will be derived from its addition.

The agri-ecosystem functioning is driven by energy and its yield potential by the present biotic and abiotic environment. The greater the energy input and the higher its retention within the system, the more fertile the soil. Balfour (1976) defined soil fertility as “the capacity of soil to receive, store and transmit energy”.

The learned response is plants obtain (the majority of) their energy from light through photosynthesis, and that is absolutely correct. In addition to photons, plants only need access to sufficient air- and soil nutrients, and H20 to produce a crop; also correct. However, this represents only halve of the energy cycle. It’s what happens in the balance of the energy cycle that determines soil fertility and to a great extent the actual portion of yield potential realised.

Whereas plants are responsible for the first halve of the energy cycle, soil organisms are responsible for the second halve and completion of the cycle. These organisms are dependent on the energy rich carbon compounds that living plants exude through their root systems and their energy containing, higher carbon content organic matter upon death or as result of root sloughing and leaf dropping whilst living. In exchange the soil organisms provide the living plant or its offspring with plant growth required soil nutrients; it’s in their mutual best interest to do so as it’s a living system with integrated components. A win for the one is a win for the other in a balanced ecosystem.

By not adequately catering for the growth supportive soil food web biology, the crop is to a great extent only reliant on the nutrients present in the soil solution, and typically added as costly fertiliser, which comprises only a tiny fraction of the total soil nutrient pool.

Sufficient energy allows soil microorganisms to mineralise nutrients from the readily available and less readily available soil nutrient pools. This directly benefits the crop, allowing improved gene expression and the realisation of its phenotypic traits.

Ignorance or wilful disregard of this very basic and fundamental process in ecosystem function is costing humanity but also directly affects the producer. The producer pays in lost and erratic yield, higher input requirements, diminishing soil fertility and smaller profit margins, to name a few.

Putting energy back into the soil

Improving soil fertility is as simple as ensuring nutrient sufficiency and increasing energy input. It can be done on a limited budget and need not affect profitability in the short term. It is all about balance. Instead of putting all your eggs into fertiliser, also keep some for additional labile and readily available carbon rich energy inputs.

Energy input is increased if the soil is kept busy, it needs living roots, the longer the better. Plant a cover crop mix and by all means have it grazed and trampled. Keep as much of your crop residue in the field as possible and do not waste money integrating it with the soil. The energy input process can also be sped-up with additional mature (low C:N) composts + manure, and activators and stimulators (compost teas, humic acids, microorganisms, etc.), when finances allow or conditions dictate.

Keep the gained soil energy by managing nitrogen fertilisation better. Ideally practice split and spread applications and cut down its use to a sensible level. If you can reach 9 tons of maize on 80kg/ha N do not push for 10 tons by using 160kg/ha, you will most certainly pay for it in time in lost soil fertility, if not already.

Precision and efficiency in agriculture is important to help reduce input cost and so too is obtaining good crop yields. However, the goal in agricultural production is (should be) to make money by increasing net profit. In addition and simultaneously therewith is increasing the return on investment and cash flow. That keeps the producer in business for the long-term but only if care is taken of the soil as production machine, and only if the soil is not being depreciated like other machines that are ultimately written off.


  • Balfour, E.B. 1976. The Living Soil and the Haughley Experiment. Faber & Faber, London
  • Ferreira E.M., Simões N., Videira e Castro I and Carneiro L. 2010. Relationships of Selected Soil Parameters and Natural Pastures Yield in the Montado Ecosystem of the Mediterranean Area Using Multivariate Analysis. Silva Lusitana 18(2): 151 – 166


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