The Response of Crops to Potassium Placement Depth and Band Spacing

Project report February 2015.


Overview
The aim of the project is to explore responses to different K application strategies (place, rate and with other nutrients) for a range of crops grown in southern and central Queensland in modern no-till opportunity cropping systems. Previous research (Mike Bell) identified that P, K and S were often co-limiting especially in the subsoils of these heavy soils, although critical soil test values (for P and K) were poorly defined. The hypothesis being tested was that on low soil test sites, providing high rates of banded K would overcome a K limitation for several crop cycles, providing other nutrients were not limiting.

Experiments in the series were at Brookstead (wheat winter 2011; sorghum summer 2012/13), Warra (cotton summer 2011/12; summer 2012/13), Gindie (sorghum summer 2011/12; chickpea winter 2012), Capella (chickpea winter 2012; wheat winter 2013; chickpea winter 2014) and Chelmsford (wheat winter 2014). The Brookstead and Warra sites were terminated in 2013. The Gindie, Capella and Chelmsford sites are all sown to sorghum to assess the residual value of the fertilizers applied earlier.

Summary to date.
· Using soil test critical values has shown to be inaccurate at predicting crop response to applied K. This is likely a consequence of water distribution relative to rooting pattern of different crops.
· At the central Queensland sites in year 1 (a good year) both sites showed a 20% grain yield response to deep P. While no other nutrients affected grain yields there was a suggestion of an additive effect of deep K at Capella in chickpea biomass. There was no S response.
· In year 2 (much drier) the effects of deep P were still evident at both sites and the effects of K were clearly evident at Gindie. There was a suggestion of an additive P + K effect at Capella and a very significant additive effect of P + K at Gindie. Improve K supply when P was also present gave a 51% grain yield increase.
· In year 3 (also dry), the responses at Capella were similar to those on wheat (2013) and chickpea (2012), with around 20% increase to K where P and S were provided.
· Around a 10% yield response to K was found at Chelmsford (wheat 2014), which depended on adequate P availability.

Lessons from the experiments:
· There is no point doing a K experiment unless P and other nutrients demands are also met.
· Deep placed K can show significant responses on different crop types, and the response depends on adequate supply of other nutrients, especially P.
· Chickpea and sorghum appear more responsive than wheat or cotton.
· In this opportunity cropping system, high rates of deep place nutrients will remain available and provide crop responses over several crop cycles, and is a financially viable nutrient management strategy.
· These experiments show that as soils reserves decline, it is essential to apply the right combination of fertiliser nutrients to maximise crop productivity and seasonal water use efficiency.


Summary of results from 2014
a) Capella Chickpea
Due to drought conditions across much of central Queensland for most of 2014, the first planting opportunity was for chickpeas at Capella. There were no planting rains for winter crop at Gindee. The grain yields over the three crops at GIndie are shown in Figure 1.
In the 2014 crop, a K response only appears when there is adequate P available. Of interest is that once P and K deficiencies were addressed, there was a small response to S. A similar S response was seen in the first year at this site, which was also in chickpea, reflecting this crops higher demand for S compared to cereals. This pattern of responses is consistent across the three years of the experiment which indicates that the relatively high rates of nutrients banded before the 2012 chickpea crop are still available to the third crop sown.
The relative yield response to the residual K where P and S were present was around 20% in the chickpea crop.


Figure 1. Yields of chickpea (2012), wheat (2013) and chickpea (2014) at Capella in Central Queensland in response to P, K, S and micronutrients banded at 20 cm before the first chickpea crop in 2012.

b) Chelmsford wheat
A new experiment was initiated at Chelmsford (near Kingroy) in 2014. This experiment again banded P and K compared to an unfertilized control, and compared 4 rates of K (O, 25, 50 and 100) where 40 kg P/ha applied. It also compared the response of 100 kg K/ha where P was present or absent. There was no rain at the site from planting until grain filling, and only 20 mm during the whole cropping season, and despite this very good yields were achieved. The results of this are shown in Figure 2.
Where 100 kg K/ha alone was deep banded, there was a 0.3 t/ha yield increase, but where there was adequate P, the response was 0.6 t/ha, so that the response to K was dependant on have adequate P available. The highest yields occurred where 50 kg K/ha and 40 kg P/ha were supplied, and there was a good response curve to added K. The addition of P stimulates root growth and proliferation and somewhat reduces the response to added K probably because a more vigorous root system is better able to forage for soil K.


Figure 2. The response of wheat to K up to 100 kg/ha, with and without 40 kg P/ha at Chelmsford, Queensland.

Table 1. Effect of added P and/or K on P and K uptake in wheat biomass.


Table 1 shows the P and K uptakes by the wheat crop at maturity and shows that K was accessed around 20 kg K from the banded fertilizer. The uptake of P and its interaction with K is less clear, as the data do not show consistent trends.

Subsequent activities
Capella, Gindie and Chelmsford sites have all been sown to sorghum in December 2014 or January 2015 following good summer rains. This will provide an additional evaluation of the residual benefits of the deep placed nutrients over two (Chelmsford), three (Gindie) and four (Capella) crops. Two photographs of the wheat crop at Chelmsford are shown below.

Communication Activities
· A short video of Dr Bell on deep placed nutrient work done (November 2014) - http://www.extensionaus.com.au/understanding-managing-multiple-nutrient-deficiency/
· GRDC also published a summary earlier in 2014 - http://grdc.com.au/Media-Centre/Ground-Cover-Supplements/GCS108/Deep-soil-tests-reveal-northern-nutrient-deficiencies
· An abstract on the research project has been submitted for presentation at the 2015 Australian Society of Agronomy conference at Hobart in September.
· A one page summary of the research to date suitable for regional agronomists was prepared and provided to Agrow P/L in 2013, and was loaded onto the IPNI ANZ website as well.
· Dr Norton presented an overview of K responses to the GRDC advisors update at Adelaide in February 2014 http://anz.ipni.net/article/ANZ-3197. This was also reported in GRDC Ground Cover through http://www.grdc.com.au/GC111S-Potassium (June 2014).
· Dr Bell wrote a paper for the Pulse Growers Newsletter in February 2014 (provided to Agrow P/L February 2014).
· Summaries of research have been loaded onto the IPNI ANZ website at http://research.ipni.net/project/IPNI-2010-AUS-13
· During 2014 a K responsive site was identified in the Victorian High Rainfall zone near Lake Bolac. The observations were circulated by Twitter and email – linked to http://anz.ipni.net/article/ANZ-3211.
· Through the current activities, Dr Bell was invited to attend a special side-meeting as part of the International Soil and Plant Analysis Council in Kona, Hawaii convened by IPNI to develop improved techniques for developing and interpreting K soil tests. IPNI provided support for Dr Bell to attend this international meeting.