Effect of rate and timing of K on three crops

The effect of potassium fertiliser applied to yellow sand for the growth of wheat, canola and lupin.

RF Brennan

Western Australia Department of Agriculture and Food, 444 Albany Highway, Albany, WA 6330, Australia. Email: ross.brennan@agric.wa.gov.au

In a glasshouse experiment, wheat, (Tritium aestivum L.), lupin (Lupinus angustifolius L.) and canola (Brassica napus L.) was grown on a yellow sandy earth from the field site where the K had never been applied. The Colwell soil extractable K was 26 mg/kg, a soil test level expected to be deficient for the growth and yields of wheat, lupin and canola,

Several levels of K, as sulphate of potash were plied to give a range of K additions from deficient t an adequate supply of K for dry weight of shoots and grain (or seed yield). The K was applied at 4 growth stages through the season. The timing of application ranged from 2-3 leaves through to boot stage of cereal and bud formation for the canola and lupin.

Glasshouse Experiment

The air-dried soil was passed through a 3.8 mm sieve, and collected in polyethylene lined bags.

The soil was thoroughly mixed before being potted into 16.5 cm diameter pots lined with polyethylene bags. To each pot containing 3.3 kg of soil the following basal nutrients were added in solution: 500 mg NH₄H₂P0₄; 64 mg MgS0₄.7H₂0; 50 mg MnS0₄.H₂0; 15 mg ZnS0₄.7H₂0; 214 mg NH₄NO₃; 0.6 mg Na₂MoO₄.2H₂0, 0.6 mg CoSO₄.7H₂O and 0.6 mg H₃BO₃. Gypsum (CaSO₄.2H₂O) was applied at 228 mg as a solid to the soil surface. On a surface-area basis 214 mg/pot is equivalent to about 100 kg/ha.

The basal nutrients were added to the soil surface and allowed to dry. After the solutions had dried, all nutrients were mixed throughout the soil by shaking the soil in polyethylene bags. Seed of each species was sown at 12 per pot about 2 cm deep into soil watered to 75% of field capacity (9g of H₂O per 100 g soil) with de-ionise water. After 14 days, seedlings in each pot were thinned to 8 uniform plants. For the first 14 days, soil in each pot was maintained at 75% of field capacity using deionised water. After this period, the soil was regularly maintained at field capacity (12g of H₂O per 100 g soil) by frequent weighing and watering. Pots were re-randomised in the glasshouse at each watering.

At harvest, the heads/pods from the remainder of the shoots (ROS). Plant sample were oven dried, and grain (seed) dried to constant %moisture.

Statistical Treatment

Excel figures at this time. However, GenStat is available and will be used. Amounts of K cited in tables below are read from the figure listed, below.

Results

Wheat

Table 1 The maximum yield of both dry shoot, grain yield and the yield response of wheat. Also listed are the amounts of K needed to be applied to reach a target yield of either dry shoots or grain. Data from the figure 1.

maximum yield	yield for Nil K	Yield response	Amt of KA	Amt of KA
			for 12 g/pot	for 6 g/pot
(g/pot)	(g/pot)	(g/pot)
	(a) wheat dry shoots
13.7	2	11.7	170	60
12.3	2	10.3	450	70
7.2	2	5.2	n.a.	280
4.9	2	2.9	n.a.	n.a.
	(b) wheat grain yield
			Amt of KB	Amt of KB
			for 4 g/pot	for 2 g/pot
5.832	0	5.832	120	60
4.54	0	4.54	240	75
2.3	0	2.3	n.a.	300
0.5	0	0.5	n.a.	n.a.

^A Is the amount of K required to reach 12 g/pot of yield for (a) wheat dry shoot and the amount of K required to reach 6 g/pot of yield for yield.

^B Is the amount of K required to reach 4 g/pot of yield for (b) grain and the amount of K required to reach 2 g/pot of grain yield.

Conclusion: - late application is ineffective to correct severe K deficiency. To achieve about half the maximum shoot weight at time 3, about 4.5 times more K needed to be applied. Similarly for grain yield (g/pot), to achieve 2g/pot about 5 times more K needed to be applied. The maximum grain yield was halved by delaying the correction of K deficiency.

Table 2 The maximum yield of both dry shoot, grain yield and the yield response of lupin. Also listed are the amounts of K needed to be applied to reach a target yield of either dry shoots or grain. Data from figure 2.

^A Is the amount of K required to reach 9 g/pot of yield for lupin dry shoots.

^B Is the amount of K required to reach 2.5 g/pot of yield for lupin grain yield.

Conclusion: - late application is ineffective to correct severe K deficiency. However he effects were not as drastic as for wheat. To achieve about 90% -95% of the maximum shoot weight at application time 3, about 4 times more K needed to be applied. However at time 4 application, about 15 times more K needed to be applied. Similarly for grain yield (g/pot), to achieve 2.5 g/pot about 7 times for time 3 and 15 times for time 4 more K needed to be applied. The maximum grain yield was about 75% by delaying the correction of K deficiency to application time 4.

Table 3 The maximum yield of both dry shoot, grain yield and the yield response of canola. Also listed are the amounts of K needed to be applied to reach a target yield of either dry shoots or grain. Data from figure 3.

Conclusion: - late application is ineffective to correct severe K deficiency. However the effects were as drastic as for wheat but less than lupin. To achieve about 55% of the maximum shoot weight at application time 3, about 3.5 times more K needed to be applied. However at time 4 application, about 15 times more K needed to be applied. Similarly for grain yield (g/pot), to achieve 1.0 g/pot about 7 times for time 3 and 15 times for time 4 more K needed to be applied. The maximum grain yield was about halved by delaying the correction of K deficiency to application time 4. Many of the lower K application levels produced no grain (see Figure 3).

Figure 1. The effect of K application at several growth stages of wheat through the growing season on the (a) dry yield of wheat shoots and (b) the grain yield [g/pot]. The diamond is the first application at 1-2 leaf followed closed square applied about 3 weeks later, and then every 2 weeks until boot-head emergence at time 4 [closed square blue]. Excel fits to data.

Figure 2. The effect of K application at several growth stages of lupin through the growing season on the (a) dry yield of wheat shoots and (b) the grain yield [g/pot]. The diamond is the first application at 1-2 leaf followed closed square applied about 3 weeks later, and then every 2 weeks until flower emergence at time 4 [closed square blue]. Excel fits to data.

Figure 3. The effect of K application at several growth stages of canola through the growing season on the (a) dry yield of wheat shoots and (b) the grain yield [g/pot]. The diamond is the first application at 1-2 leaf followed closed square applied about 3 weeks later, and then every 2 weeks until flower opening at time 4 [closed square blue]. Excel fits to data.

Acknowledgments

The work was partly funded with by of IPNI, Australia and New Zealand.