By David Jones, Broad Acre Agronomist, Msc. Agriculture

A couple of months ago I looked at the gross margins of different crops in order to understand their profitability. We all know of course that the cash that a crop generates after seeds, sprays and fertiliser costs is not the be all and end all, and that we should take into account the wider benefits across the rotation. 

Two interesting things have happened this week with Sunflowers that have made me realise just that…

A respectable crop of barley or wheat will normally produce a gross margin of 120,000 ksh/ha, far more than even a high yielding (2.5 t/ha) Sunflower crop sold at 35 ksh per kilo. The sensitivity analysis below is a very good way to understand the impact of a change in price or yield on the bottom line of a given crop, in this case Sunflowers.

After deducting seed, spray and fert costs of 35,000 ksh/ha (350 USD), it is very apparent that you need to be achieving a yield of at least 2 tons per hectare and a price above 30 ksh/kilo to make the crop even worth considering.

Sunflower Gross Margin sensitivity to price and yield (output minus 35,000ksh of variable costs).

  25 ksh/kilo 30 ksh/kilo 35 ksh/kilo
1.5 t/ha 2,500 10,000 17,500
2.0 t/ha 15,000 25,000 35,000
2.5 t/ha 27,500 35,000 52,500

But what about the benefits to OTHER crops across the rotation?

Sometimes, just looking at the returns from a single crop in isolation is very misleading, and the effect on the whole rotation needs to be understood. Last week I looked at the yield map of a field of peas that showed a very defined high yielding strip, exactly where the Sunflowers had been 2 years ago (the rest of the field was canola).

Clearly yielding over 2 t/ha above the rest of the field this is an extraordinary response, especially 24 months later, and lead me to question what was causing this.

Nutrition is the first point that comes to mind, and an Australian farmer pointed out on Twitter that the Sunflowers may have brought Zinc up from depth with their deep roots. The leaf tissue tests however did not reveal the field of peas to or the barley the year immediately after the Sunflowers to have low Zinc (35 and 68ppm of Zn respectively).

An Australian agronomist Wayne Smith made the observation that the Canola in the rest of the field is not only non-Mycorrhizal but also promotes several species of nematodes. Worth remembering too that zinc has a wonderful effect on root growth (if it is limiting) which helps overcome the damaging effects of nematodes.

Ordinarily I would suggest that this might be a moisture access and rooting effect, but given the overwhelming rainfall this season I doubt that was a limiting factor!

sunflower crop rotation

A dark green strip on the yield map where we had Sunflowers in 2016. The rest of the field was Canola.

Once we consider the additional yield in the peas or any other crop for that matter, the financial case for growing Sunflowers in the rotation is much stronger. The question on my mind now is where to put them into the rotation.

Rotational Options

For a farmer growing continuous maize or cereals, possibly on rented land but looking to get away from the monoculture without breaking the steady cash flow, putting in Sunflowers during the off season will probably have a limited benefit.

If Brome is triggered to germinate in the main planting window of March – April you are unlikely to benefit from the use of a Group A graminicide such as fluazifop in the off season, and the deep roots will remove as much moisture as you will gain from their soil structuring effect. It also won’t be long enough to break any Root Lesion or Crown Rot cycle.

For growers on established Wheat, Canola, Barley, Peas rotations there is a plausible option to put it as a double crop before a shorter season crop such as Peas that require less moisture. There is also minimal risk of herbicide carryover in this position and it effectively adds a ‘cover crop’ to the rotation rather than replacing a valuable cash crop.

On the other hand, expanding the rotation out to six years by incorporating Sunflowers and another cereal will be of great long term benefit to the canola and pulses, reducing Clubroot, Blackleg and Fusarium pressure in the rotation.

I certainly would not want to follow Sunflowers with Canola because of the Sclerotinia risk (or vice versa because of the difficulty of removing canola volunteers), and after peas would be a waste as it would not fully utilise the nitrogen held in the soil.

Many farmers in the North Rift growing continuous maize will also try to grow Sunflowers in the off season, but the residual effects of terbuthylazine + S-metolochlor + mesotrione herbicide, coupled with the high residue levels after maize mean that this is not a sensible exercise to achieve accurate planting depth and consistency.

Weed Control

There are more options that you think for weed control, some approved in Kenya and some not yet – so check before use and speak to one of our agronomists.

But our trials program has been extremely revealing in highlighting combinations of products that work across a range of weeds, even in the very tough season we have just experienced.

Sunflower farming

Five months after planting and without Clearfield – it is perfectly possible to grow weed-free sunflowers.

Mau Narok Ryegrass

I took a trip up to Mau Narok last week and wow, this has to rate as some of the best farmland I have ever seen. Forget the Paris Basin, Canterbury Plains or Lincolnshire Wolds, this has it all; consistent temperature, moisture, depth of soil.

Mau Narok

Map showing pin drop location of Mau Narok, 200kms North West of Kenya’s capital Nairobi

Mau Narok

Beautiful farm scenery in Mau Narok

The Ryegrass however is so bad, but my immediate thoughts are the need for PROFITABLE Canola break crops given the short land tenure. This requires:

  1. Clethodim herbicide in crop.
  2. Getting propyzamide or carbetamide registered here asap – cool temps would work well (and no-till – propyzamide does not like weeds coming from depth, carbetamide less so).
  3. Pre harvest glyphosate to further reduce weed seed-set.
  4. The right varieties. A Clearfield Canola with European type yield potential would take yields on 10-15% above the old Belinda, and allow the use of alternative chemistry.

The main thing to accept is that there is nothing in the pipeline of new herbicides for Ryegrass, except possibly Luximo from BASF which is still 2 years away in Europe and Australia.

Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the future of how we feed the planet.

Agventure Ltd set up the Center of Excellence for Crop Rotation to help farmers diversify cropping systems and introduce techniques which have a long-term outlook to improve soil health.

The Center of Excellence for Crop Rotation works extensively with Crop Nutrition Laboratory Services Ltd (CropNuts).

Till next time,

Take care,


About David


David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.