Cropping Inputs, Diary Number 3

[Transcript of Cropping Inputs, Diary Number 3]

Hello and welcome to the third addition of our cropping Inputs Diary. Last time, I discussed inputs into our cropping programme that we should avoid if we really want to look after the soil and increase its productivity over the long term. That is soil that is healthy with good structure, diverse and active soil life and balanced nutrients.

With all that in mind we will now go back to the soil tests from the first session and choose the inputs.  Normally we could talk an hour on one soil test but here, we will keep it short and cover it in just a few minutes.  So we have a nice medium density soil with good nutrient holding capacity. The PH is low, the cause being low calcium and partially potassium. As expected the calcium magnesium ratio is very low which is causing a poorly structured soil. Poor oxygen penetration reducing soil biological activity and therefore mineralisation of nutrients into the crop. The first application therefore is 2 and half tonnes per hectare of lime. This is a one off capital investment which should not be needed again until the next decade or two, if the soil is looked after.

Another important reason for the application of lime, is the excess of iron and aluminium. Both of which quickly lock up the applied phosphorus in the soil into an unavailable form to the plant.  This is clearly shown with a very high total phosphorus levels and the low plant available phosphorus. Also the very high number in the PBI, or Phosphorus Buffering Index, raising the calcium levels over time will unable more of this locked up Phosphorus in the soil to become more available. Clearly the use of traditional water-soluble fertilisers in this soil type is giving very poor efficiency.  In choosing a phosphorus fertiliser a form such as non-water-soluble SMS Guano has the advantage of not being so prone to locking up in this soil and therefore available to the plant.

It is also biologically friendly in the soil. The trace elements in SMS Guano will maintain the balance of these figures. Potassium is at a marginal level and particularly if growing hay crops which I believe will be a popular option in a cropping mix this year, an application of Sulphate of potash is needed. Having some sulphur will aid in maintaining the sulphur levels in the soil also.  For cereal crops a pre-sowing application of Ammonium Sulphate are more soil friendly and less leachable form of nitrogen with the added advantage of sulphur is preferred over Urea. Something to remember is a quote from a SARDI researcher who made a statement, “The more Urea that is used, the more lime you need to apply”. The result of these inputs over several years will see a marked improvement in the soil structure, bigger root structure, heathery crops better fertiliser efficiency and even some earth worms appearing.  Another soil test in about 5 years will confirm a more balanced soil and a great deal of satisfaction on achievement. The next season, we will talk about post seeding strategies.