An oats trial at Brookton last year highlighted the importance of nitrogen (N), phosphorus (P) and potassium (K) for oaten hay and grain production. ‘Hay’ production was more responsive to K than grain, and high rates of N were required to take advantage of the favourable season - N was also very effective at increasing grain protein levels.
K-Till Max (analysis: 9.6 N 9.4 P 15.0 K 6.5 S 0.12 Cu 0.24 Zn) is ideally suited to growing hay and grain on crops (and soils) that have a higher requirement for K than P. If soil reserves are very low, and high production is targeted, supplementary K for hay production is advised.
Trial details
The trial was set up to look at the requirement for N, P and K individually, with treatments included to test the benefits of pushing N and K inputs to high rates.
Soil tests highlighted K as a major concern (Colwell K 32 mg/kg in the 0-10 sample and < 20 mg/kg down to 50cm), so 150 kg/ha K-Till Max was used as the starter fertiliser to supply 14P and 23K with 100 L/ha Flexi-N banded at seeding to give us a control (‘Complete’) for testing the effect of omitting K (Flexi-N/Agstar Extra), N (Big Phos/MoP) and P (Flexi-N/MoP). The trial also investigated the importance of K to N response, and the returns from increasing N inputs to 113 kg/ha. The value of applying a higher rate of K was looked at in another treatment supplementing K-Till Max with 136 kg/ha MoP topdressed before seeding providing 90 kg K/ha – the amount of K that can be removed in a 6 t/ha crop.
So, what did we find?
This crop, like many last year was highly responsive to N, and high N (and K) inputs produced nearly 8 t/ha when ‘hay cuts’ were taken. There was a 2.5 t/ha dry matter (DM) response to 56N, and an additional 0.7 t/ha response to increasing N inputs to 113N with 134 L/ha Flexi-N applied during tillering.
Omitting P and K from the ‘Complete’ treatment (supplying 56 kg N/ha) reduced DM production by 1.8 and 2.1 t/ha respectively (Colwell P was 33 mg/kg, PBI 38).
And K supply was critical to the returns from N. Without K, there was only a 0.8 t/ha response to 56N; but with 23 K supplied (using K-Till Max), there was a 2.5 t/ha response i.e. a three fold increase in returns from N fertiliser.
When grain was harvested, yields varied from 2.3 to 4.0 t/ha and N responses were again strong (not surprisingly). There was a 1.2 t/ha response to 56N, and an additional 0.4 t/ha harvested when N inputs were increased 113N.
Where 56N was applied, there was a 0.4 t/ha response to 14P, but while there were small yield responses to K, they were not statistically significant.
The impact that N supply can have on grain protein was evident with increases from 10.1% (0N) to 10.8% (56N) to 13.5% (113N).
Treatments and results
Response to Nitrogen - 20 September 2018
