Hamilton Based Independent Soil Scientist Dr Gordon Rajendram (PhD), Discusses Healthy Soils In New Zealand.

Healthy soil and pasture production rely upon the correct soil testing process. Let’s take a look at two key factors that drive pasture production.

The first key factor is soil temperature at 10cm. At 5 or 6 degrees, the pasture stops growing.

The second key factor is soil moisture and the significant impact on pasture production with soil moisture < 25%.

A Field Collaborated Soil Test at this stage will help you find the maximum pasture production between low productivity and wasting money.

At this point, I would like to highlight that pasture species do not thrive in low-pH soils in addition to the two critical factors named above. Why is this?

In simple terms, it is due to the increased Aluminium in the soil solution, which retards root growth – the implication leading to less growth of herbage on top.

Currently, many soils are very acidic (<5.5pH). Farmers could alleviate this problem by applying lime to eliminate soil acidity.

However, with the proper testing and planning, every budget has room to include lime and fertiliser as part of pasture management programmes.

You may have heard in the news recently about the impact Leaching is having on our soils. 

Leaching is the loss of water-soluble plant nutrients from soils. Factors such as rain and irrigation are contributing factors. The result – amounts of nutrients are lost via sub-service flow related to the amount of rainfall and drainage. 

We see the knock-on effect with essential nutrients in plants. These exist as anions and cations – the leaching of anions and cations is conditional on various factors including, but not limited to, the amounts and form of nutrients applied in fertiliser, stocking rates, drainage, soil types and the previous extent of soil leaching.

Plant growth is dependent on a critical element – Phosphate. Applied phosphate must remain in the soil and not run off as particulate P or leach into subsoils. 

So how can we mitigate P losses?


  • < 40% ASC greater potential to lose P from soil
  • Apply a little bit often
  • Essential to use the right product
  • Apply slow-release P & S products
  • Combo of water-soluble/slow-release P & S

I want to emphasise two critical factors.

  • Anion Storage Capacity (ASC), or Phosphate Retention (P-retention), is a measure to remove P from the soil solution. It is a crucial test and should be included with every sampled area to determine levels.

I cannot stress enough the importance of this information when factoring in using phosphorus and sulphur fertilisers.

Secondly, it is essential to remember that fertiliser is only one aspect of a productive management system. If you don’t test properly, you are doing yourself a disservice to your business.

As an Independent Fertiliser Consultant, I am dedicated to helping all farmers get the most out of their soils so their farm, their most significant asset, works more efficiently and sustainably for increased profitability.

“To forget how to dig the earth and to tend the soil is to forget ourselves.” -Mahatma Gandhi.

Dr Gordon Rajendram is a New Zealand Independent Soil Scientist specialising in Soil Fertility, Agronomy & Farm Environmental Consultancy.

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