In this Think Agronomy issue:

  • Are you diagnosing Fall Armyworm correctly in Sorghum?

  • The benefits of liming and why it remains the most cost effective input

Getting The Basics Right

The importance of getting the basics right in farming is something I often talk about in #THINKAGRONOMY newsletters. Having the most up to date sprayer or fertiliser spreader is of little consequence if you do not put the right materials through it, or give your crop the best start by planting it well.

For well over a hundred years we have known the importance of getting the pH right before any other fertiliser inputs or crop protection measures.

Many of the crops we grow have been selected to be tolerant to acid soils, but this does not mean that yield still won’t respond positively to lime applications. Take a look at the list below – anything moderately sensitive to pH really needs a soil of at least pH 6 to achieve their full potential.

Agricultural Lime

Increased Nutrient Availability

The second crucial point is that maintaining a correct soil pH drastically improves the availability of many nutrients. The classic graphic below reminds us that here in Kenya for example where we are usually short of P, Mg and S, a low pH is costing us further in reduced nutrient availability.

Agricultural Lime

One argument that is sometimes put forward is that it is cheaper to replace these nutrients or to top them up than it is to lime. But are these nutrients still being used efficiently? The evidence below suggests not:

Agricultural Lime

At a pH of 5, for example, only 30% of the phosphate is recovered; raise the pH to 6 and nearly 90% is utilised by the crop. Attempting to make this up with applied P fertilisers would not only be futile but prohibitively expensive.

The amount of lime needed depends on the starting pH of your soil and the type of soil. Getting a soil test and a recommendation is the surest way to know what the optimum amount of lime is.

Test the soil thoroughly by taking several sub samples from across the field and mixing together, and remember to test any different areas of soil separately – if there are areas that don’t need lime this will pay for the extra soil test a thousand times over.

Agricultural Lime Spreader

Agricultural Lime Spreader

Does Lime Need To Be Physically Incorporated In A No-Till System?

This is a real quandary for many committed notill growers who are well down the road of building their soil structure and extremely reluctant to undo it by cultivating to incorporate lime.

If you want to learn more, some of the comprehensive work to cover this area has been done by the GRDC in Australia and can be found here:

In the next Think Agronomy newsletter, we’ll discuss the pros and cons of different lime products and go into greater detail on the effectiveness of different lime products.

Fall Armyworm Identification 

Which of the pests below is a Fall Armyworm? Go to my Twitter page for a video on identification.

Fall Army Worm
There are a lot of Sorghum crops in the ground at present and many growers are confusing the Syrphid Fly larvae (the left and middle photo) with the Fall Armyworm on the right.

Syrphid larvae are your friend! They eat large numbers of aphids in Sorghum and do no damage to the plant. In areas that are experiencing cooler nights around 9C, I am actually seeing very few Fall Armyworm in Sorghum.

Be vigilant however, as these are the slower growing crops that remain vulnerable to Fall Armyworm for a longer period.

Till next time,


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.