We have seen some interesting responses to sulphur over the last two years of our trials, and one of the key questions I am asked is “What is the best way to apply Sulphur?”
Bearing in mind that the best way is not always the cheapest way, I have broken down the cost of various topdressing products to look at what happens if the weather forecast for the end of the month is right and we are expecting rain.
So, how do we cut through the confusion of products with different amounts and ratios of Nitrogen and Sulphur for topdressing? One simple way is to work out the value of the Nitrogen based on how much Nitrogen costs in its simplest form, Urea.
If we use a rough price of $450 or Ksh. 45000 per ton (which contains 460kg or 46% Nitrogen), the cost per kilo of actual nitrogen is $0.98 or 98 Ksh.
So, taking a 40N + 6S urea + sulphur product, we know that the value of the nitrogen is 400kg N x $0.98, or $392. The sharp-eyed will notice that the purchase price of this product is around $500 per ton, so we are in effect paying the difference – $108 – for the benefit of the Sulphur.
There is 60 kilos per ton of sulphur in this product so the cost for each kilo is therefore $1.80. This is a great and simple way of looking at the cost… which varies enormously between products.
|Product||Cost per ton ($)||Value of Nitrogen at Urea price ($)||Cost of Sulphur $
(Total cost minus value of N)
|Cost per Kilo of Sulphur ($)|
|Controlled release 40+6S||530||392.00||138.00||2.30|
|Ammonium Sulphate 21+24S||340||205.80||134.20||0.56|
|Magnesium Sulphate granular 14S||430||430.00||3.07|
There are of course subtle differences between the products – Controlled Release Urea works out slightly more expensive but may be very worthwhile where the volatilisation risk is high.
Ammonium Sulphate is still the cheapest way to buy sulphur but it is very difficult to spread accurately. If you are side dressing this is not an issue, but on 18m+ tramlines the striping and yield penalty will be high. It is also very acidifying, but of course lower doses are applied because of its high Sulphur content so one could argue that this is relative.
Sulfammo is a very high quality product that spreads well and has the added bonus of Calcium and Magnesium. Unfortunately, whilst these two elements are very useful, at topdressing time they will only have a small impact on the current crop but will be of some value to future crops.
Finally, consider the ratio of N:S that you are targeting based on local experience, soil tests and the advice of your agronomist.
Potatoes – keeping the crop weed free
With most of the country’s potato crop unplanted until the rains hopefully arrive, what are the key herbicide options for the crop?
- Metribuzin – Depends on the tolerance of the variety – check that it is safe to apply. Good on brassica weeds, Fathen (chenopodium) and helps on Amaranthus and Gallant Soldier.
- Flufenacet – Adds Nightshade control and Fathen, and is generally very safe on the crop even in heavy rains. At high doses it gives very useful control of Cleavers which can be extremely detrimental to yields if left unchecked.
- S-metolachlor – Good on Fathen and has reasonable activity on Amaranthus, Brassicas and Watergrass. Generally fairly safe on the crop but needs moisture to be reliable.
- Linuron – do not apply before heavy rain as this has a tendency to wash through the ridges and can slightly affect the crop. Good on Nightshade and Fathen.
- Stomp – Good on grasses, Fathen and has some activity on Gallant Solider. Weak on Brassicas and Cleavers. Must be applied well before the crop is due to emerge to avoid damage, and needs 48hrs to bind fully to the soil before heavy rain.
- Clomazone – Very strong on Cleavers but can struggle on high organic matter soils. Weak on Fathen and can yellow the crop. Mixed with Linuron it can be very effective on Bindweed. Surprising how effective it is after several weeks of dry conditions once rain arrives.
Know your weed spectrum before you plant. It is important to remember that every potato variety, crop and location are different so ALWAYS consult an agronomist. The above guidelines are not a recommendation.
Maize Nematodes – The Silent Root Killer
If this dry and tough season has taught me one thing, it is that poor roots – and NOT lack of soil moisture – that is crippling maize crops in many parts of the country. Take a look at the trial below at our Nakuru site, with a plot of 6218 planted into good moisture after maize last year…
Yes, the crop looks stressed and dry as if its roots are not accessing the moisture, but taken a look below when we add some in-furrow nematicides at planting…
The plants are healthier, greener, larger and more uniform as the roots are not being attacked by nematodes. In a ‘normal’ rainfall season we probably wouldn’t see the visual difference like we can here, but this really exposes the fallacy of growing maize on maize continuously.
Previous soil analysis for nematodes on this farm has showed high levels of Meloidogyne (Root Knot Nematode) and Pratylenchus (Root Lesion Nematode) so this is not a surprise.
Nematicides are only a short term fix, what this really cries out for is rotation with crops like Sunflower and Linseed. Just don’t confuse drought with poor, short-term farming practices.
Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the futureof 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,
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.