تعیین حد بحرانی پتاسیم با عصاره‌گیر استات آمونیوم در شالیزارهای گیلان

Potassium is one of nutritional element that has an important effect on the quantity and quality of rice plant. Knowledge about the K critical level and plant response to different application rate of K, can effectively help with the proper use of this element. Therefore, in this study potassium (K) critical level for rice (Khazar variety) and prediction equation for grain yield were determined in 21 rice fields of Guilan provience during 2001-2002. After land preparation, 6 experimental plots (4×5m) were constructed in each selected field. Nitrogen and phosphorus were applied before transplanting, based on soil test from urea and triple superphosphate, respectively. Potassium was applied in different rates including 0, 100, 200, 300, 400, and 500 kg ha-1 of K2O as muriate potassium. Khazar variety was transplanted in a space of 25×25cm, just after fertilizing of plots. Plots were harvested in 5 m2 at the end of maturity stage from the first node above the ground, and grain and straw were measured separately. Statistic analysis was done on grain weight based on 14% moisture. The results showed, that effect of different K fertilizer application in 5% and the effect of soil type in 1% were statistically significant on the grain yield. The mean increase of grain yield in responsive fields to K application was 982 kg ha-1. The results also showed that the responses of rice fields with available K less than 100 mg kg-1, 100-160, and more than 160 mg kg-1 to KCl application were high, moderate and low, respectively. Potassium critical level based on 90% relative yield was determined as 110 mg kg-1 of soil . In final relative yield, prediction equation, available potassium, potassium content of irrigation water, and rate of KCl fertilizer application entered positively in the equation, while available phosphorus showed negative effect on relative yield.