The Response of Crops to Potassium Placement Depth and Band Spacing

It was planned to recrop the sites at Gindee and Capella with another winter crop (wheat or chickpea) following the sorghum crops harvested in April at both sites. Unfortunately there was no stored water in the soil profile and so the paddocks were not sown. As a consequence, this finishes the Canpotex involvement with this project which goes back 2011, initially with sites in southeast Queensland, and then subsequent experiments which showed responses in Central Queensland.
A summary of the three crops at Gindee (Sorghum, Chickpea, Sorghum) and Capella (Chickpea, Wheat, Chickpea) was presented at the 17^th Biennial Australian Society of Agronomy Conference and a one page summary prepared for wider distribution and provided to Agrow. The results from the 2014/2015 sorghum crop has been added to this one page summary and this is attached to the report along with the paper presented at the conference.

A short summary of the key results is also provided below:

· Yield response to deep placed P, K and S aggregate grain yield over three or four years as a percentage of the untreated control are shown in Table 1.1 below. This shows that improving subsoil nutrient supply can give yield increases of 10% to 20% where both P and K are addressed in these soils. The largest responses at both sites occurred where both P and K were supplied together. This indicates that these nutrients are co-limiting and so addressing both is important in achieving water-limited yields in this environment.

Table 1.1. Aggregate grain yield over three or four years due to deep placed nutrients as a percentage of the untreated control.

	K	P	S	PK	PS	KS	PKS
Gindee	113%	111%	101%	125%	113%	110%	120%
Capella	103%	108%	102%	111%	110%	103%	113%

· Nutrient uptake was monitored in these experiments and this is summarised in the two figures (Figure 1.1) attached which cover the first two years of the experiment. In terms of nutrient uptake, K uptake was higher in the first crop year than the second crop year. The highest cumulative K uptake occurred with the combined P and K treatment. In that treatment, approximately 80% of the K applied (200 kg/ha) was taken up by the crops, and this was more than either the P or K alone treatments. The improved root growth probably because the P supplied enabled better access to the K bands.

Figure 1.1. The uptake of K at peak biomass at Capella (Top) and Gindee (Bottom) for the various nutrient treatments over two years in Central Queensland. K uptake is the product of biomass and plant K concentration.

Another site was established at Chelmsford (40 km north of Kingaroy) in 2014 and sown to wheat and then sorghum. The key findings from this site were consistent with the work undertaken in Central Queensland.

Conclusions
The Results from two sites (Gindee and Capella in CQ)

• Season and crop affected responses
• There were responses to P alone in the first two crops at each site & K responses in half the six site years.
• In year 1 (a good year) a 20% grain yield response to only to deep P.
• In year 2 (much drier) gave a smaller P response, but K responses were seen at Gindie. Indication of an additive P+K effect at Capella and a 50% increase for P+K at Gindie.
• Year 3 was dry and chickpeas at Capella showed a larger response to P+K but the sorghum at Gindie only responded to deep K.
• The results at Chelmsford showed significant responses when both P and K were supplied.
The Practice Change
• Deep placement of P and K gives a sustained response over at least 3 years and across different crops and seasonal conditions.