Effect of different potassium fertilizers on the yield and their efficiencies on two paddy soils with different potassium levels in Mazandaran Province

Rice (Oryza sativa L.) is one of the most important crops in the world. After nitrogen, potassium plays the most important role in increasing rice yield.

In spring of 2017, in order to investigate the role of different sources of potassium (K) in increasing rice yield and their efficiencies, two experiments were implemented in two rice fields. The First experiment was conducted in a randomized complete block design with 7 treatments and 3 replications in a total of 21 plots (20 m2 each plot) with Shirudi cultivar in a paddy with soil available potassium 136 mg kg-1. The treatments were as follows:T1=Control (using all fertilizers based on soil analysis results except Potassium); T2=Farmers conventional fertilization method (NP); T3=T1+250 kg ha-1 potassium sulfate (SOP) before plantation; T4=T1+125 kg ha-1 SOP before plantation+115 kg ha-1 potassium chloride (MOP) in two splits along with urea top dressing; T5=T1+125 kg ha-1 SOP before plantation+105 kg ha-1 SoluPotasse (SP) in two splits along with urea top dressing; T6= T1+ 125 kg ha-1 SOP before plantation + 105 kg ha-1 soluble potassium sulfate (SSOP) in two splits along with urea top dressing and T7=T1+125 kg ha-1 SOP before plantation+105 kg ha-1 SSOP+ zinc chelate in two splits along with urea top dressing. The second experiment was conducted in a randomized complete block design with 4 treatments and 3 replications (200 m2 each plot) with Tarom cultivar in a paddy with soil available potassium 465 mg kg-1. The treatments were as follows:T1=Farmers conventional fertilization method (NP); T2=T1+50 kg ha-1 MOP in two splits along with urea top dressing; T3= T1+50 kg ha-1 SSOP in two splits along with urea top dressing; T4=T1+50 kg ha-1 SSOP+ zinc chelate in two splits along with urea top dressing. The results of the first experiment revealed that: a) while the paddy yield in the control plot was 8325 kg ha-1, it increased up to 12148 kg ha-1 (46% increase) in T7 and it was significant at 1% level; b) while the head rice yield (HRY) in control treatment was 49.6%, it increased up to 56.4%, in T7 and it was significant at 1% level and c) while K-fertilizer efficiency in T3 was 2.73 kg kg-1, but in the best treatment (T7) increased up to 16.98 kg kg-1. The results of second experiment revealed that while the paddy yield in the control plot was 5109 kg ha-1, it increased up to 5479 kg ha-1 (7.2% increase) in T4 and it was significant at 1% level.

Considering to the above results, it can be concluded that a) K-fertilizers causes significant increase in the paddy yields especially when soil available K was lower than its critical level (250 mg kg-1). However, this increase will be much more effective if 50% of the K-fertilizer needs to be apply before planting from SOP and remaining 50% supply from SSOP+Zinc chelate. b) If in the paddy soils, soil available potassium is higher than its critical level, the use of pre-plant SOP was not effective, but in this case, split application of SSOP especially SSOP+Zn chelate will be economically effective.