Best management practice of potassium for sunflower (Helianthus annuus, L.) in Northwest China

The purpose of this project was to establish best management practices for K in sunflower for Northwest China after three years (2014 to 2016) of study on right source, rate and timing of K fertilization.

Potassium application significantly increased total dry matter, seed yield, head diameter, weight of 1000 seeds, kernel rate, and oil content. In Gansu, 16 of 20 sites, and all 20 sites in the Inner Mongolia Autonomous Region (IMAR), showed positive seed yield response to K with respective averages over K omission plots of 14% and 11%. Potassium application did not affect seed quality indices of oil sunflower in Gansu, while it significantly decreased the content of saturated fatty acids, and increased the content of unsaturated fatty acid of edible sunflower seeds in IMAR. The mean agronomic efficiency (AE) of K was 4.9 kg seed/kg K₂O in Gansu and 3.4 kg seed/kg K₂O in IMAR. In Gansu, average indigenous K supply was 309 kg/ha, and average productivity was 3,800 kg/ha. In IMAR, average indigenous K supply was 176 kg/ha, and average productivity was 3,050 kg/ha. The average N, P and K required for producing 100 kg of oil sunflower seed was 4.07 kg N, 2.15 kg P₂O₅ and 10.23 kg K₂O. Similarly, the requirement for producing 100 kg of edible sunflower seeds was 3.59 kg N, 0.55 kg P₂O₅ and 7.65 kg K₂O.

The first-year trials showed no significant differences for seed yield, total K uptake, disk diameter, weight of 1000 seeds and kernel rate between sources and times of K application. Sources and times of K application did not significantly affect seed quality indices of oil sunflower in Gansu, while K₂SO₄ produced higher oil content and saturated fatty acid, and less unsaturated fatty acid than KCl for edible sunflower in IMAR.

An experiment on the interaction between K rate and water regime conducted for edible sunflower in IMAR found that drip irrigation produced the highest total dry matter, seed yield, disk diameter, 1000-seed weight, kernel rate, and total uptake of K and Cl^-. This treatment was followed by rainfed plastic mulch practices and then rainfed without mulch. The average AE for K was 4.3, 3.0 and 1.0 kg seeds/kg K₂O for sunflower with drip irrigation, rainfed plastic mulch, and rainfed without mulch, respectively. Agronomic efficiency for K decreased with an increase in K rate. With a proper water supply, a higher content of saturated fatty acid was observed, in contrast to the lower the content of unsaturated fatty acid. Potassium application rate did not influence seed quality indices except fiber content, which decreased as K rate increased.