Potassium responses in winter crops and pastures

In 2014, in collaboration with Landmark agronomist Ed Hilsdon, a wheat crop near Lake Bolac in Western Victoria showed windrow effects from the prior canola crop. Crop growth was better in the windrows than between the windrows and a K deficiency was diagnosed by tissue tests. Western Australia also reported that “Wavy Crops”, ie where old windrows are showing up as good growth in the subsequent crop, are a reliable indicator of potential K response.
Soil exchangeable K test values in the windrows are: 57 (0-10), 30 (10-20), 27 (20-30) and between the windrows are: 43 (0-10), 27 (10-20), 23 (20-30). Based on soil test critical values (~40 mg/kg Colwell K or exchangeable K), the windrows are above the critical value, while between the windrows would be responsive to added K.
This site has been used for an experiment in 2015 to follow up this response, which could also be due to raised pH under the burned windrow. The 2015 experiment has liming treatments across the windrows and top dressed K at 4 rates (0, 25, 50, 100 kg K/ha as MOP) was applied with and without lime and on and between the windrows. Wheat and barley will be sown as the test crops, giving 32 treatments in total, with 4 replications. This site has been supported mainly through the GRDC project to develop more data to go into the Better Fertilizer Decisions for Crops database. The site was sown and managed by Southern Farming Systems and Landmark, led by Dr Jonathan Holland (NSW DPI Wagga Wagga).
The crop was inspected in early July with a group of local farmers, and the windrow responses were showing up quite clearly and in a small demonstration next to the experiment. In all cases, better growth was seen where K supply was enhanced.
Conditions during spring were harsh and low rainfall and high temperatures meant that yields were suppressed, so making expression of K or lime responses difficult to assess. However, the yield responses of wheat and barley to applied K in the inter-row area with no lime is shown in figure 4.1. This figure shows the response of these two crops to applied K in the interrow (low K) limed and unlimed.
The overall results are still to be fully interpreted and the seasonal conditions reduced yields from what should have been 4 to 5 t/ha to less than 2 t/ha at this site, as well as the whole district. There may be interacting effects of lime and K rate within or between the prior windrows. There does appear to be some yield depression with the higher rates of K in the windrow (ie very high K). These data also indicate that barley is less responsive to K than wheat and may suffer yield depression under high K rates. Table 4.1 shows the yield comparisons between limed and unlimed treatments at nil applied K and 50 kg K/ha.

Figure 4.1 The response of wheat and barley to added K within and between the prior crop windrows (preliminary results only).


Between the windrows, there appears to be a response to lime in wheat, and the K for wheat appears to provide an additional benefit in those conditions. There is almost an additive response of K and lime in wheat. Barley has not shown this response. The subsequent analyses may reveal more from these results.

Conclusions

· Results are yet to be fully analysed but it appears that a good response to K was seen between the windrows in wheat.
· Barley appears less responsive to K, and also less responsive to liming.
· The appearance of better growth in windrows from the previous crop does appear to provide a good field diagnostic to the potential response to K in this region.