Since the year 2000, rainfall in the Northern ag region of W.A has roughly decreased by 3 inches during the growing season. This rainfall has been lost in the period between May – July, meaning that follow up rainfall events after a break to the season are less likely. This increases the likelihood of fertiliser toxicity for all crop types particularly on sandier textured soils, which can rapidly dry. Lupins are particularly susceptible to fertiliser toxicity, because if the germinating radicle is desiccated by the salting effect of the fertiliser, there are no other roots to compensate and the seed dies.
The effects of fertiliser type and placement on the germination and growth of lupins has been demonstrated this year in a trial conducted by CSBP on the Northern Agri Group’s main trial site at Binnu.
The soil type was yellow sand plain, typical of a lot of the soil in the NAR. The site was sown on 24 May with 100 kg/ha barlock lupins following 18mm of rain on 21 May. Warm conditions following the rain saw the moisture in these sandy textured soils rapidly retreat deeper. The site was sown with a Conserva Pak Tyne system on nine inch row spacing. Fertiliser was either top-dressed, drilled with the seed or banded an inch below and slightly to the side of the seed.
The initial germination of lupins was very poor (less than 1 plant/m2) for all treatments. Follow up rain did not occur until the 23 June with 6mm. Subsequent rains were reasonably frequent but small with the site accumulating 47mm from the 23 June to the 31 July. This pattern of rainfall promoted several germination of lupins over that period. By early September there were some obvious establishment differences between treatments. Plant counts were carried out on the 18 September to verify visual observations. Results are shown in the table below.
Where fertiliser was top-dressed, plant establishment was similar to where no fertiliser was used. With the Conserva Pak System, when we drilled or banded the fertiliser, lupin plant numbers were reduced. In general when we drilled or banded, if MOP was added to the fertiliser mix toxicity seemed to be worse, and where MOP and nitrogen (K) were added (i.e K-Till Extra Plus), the toxicity was worse again.
Left: 110kg/ha Super Phos + 50kg/ha MOP (Topdressed) Right: 57 kg/ha Double Phos + 50kg/ha MOP (banded below the seed)
Left: 57 kg/ha Double Phos (banded below the seed) Right: 110 kg/ha Super Phos (topdressed)
The results from this trial are from using a Conserva Pak Tyne System. There are many other seeding systems that growers are using which may not give the same level of toxicity when seeding lupins. However, if growers are banding their fertiliser they need to know how far below the seed it is being placed.
As this trial has shown, even banding fertiliser an inch below a lupin seed can still cause toxicity problems particularly if the soil is of a sandy texture and rapidly drying. In general top-dressing fertiliser onto lupins causes no germination issues, but when drilling or banding, the potential for toxicity issues are increased. The type of fertiliser used when drilling or banding does not eliminate the likelihood of toxicity, but if we add MOP or a nitrogen containing fertiliser to the mix, we can increase the potential of fertiliser toxicity.