Determination of phosphorous critical level in rice growing area of south of Iran
2006
Kavoosi, Masoud | Morshedi, Ali | Jafarnejadi, Ali Reza | Gilani, Abdol Ali | Jafarzadeh, Sohrab | Masoudi, Behnam | Farzan, Majid | Hady Ghanavat, Moen | Hardani, Jaber
In order to determine, phosphorous critical level in rice growing area of south of Iran, and to investigate the effects of P fertilizer application on rice grain yield, this research was conducted in paddy fields of Khuzestan, Chaharmahal va Bakhtiari, Fars and Isfahan provinces. 100 surface soil samples (0-30 cm) with a good geographical distribution were collected from different paddy fields of each province by use of G.P.S. apparatus. Soil samples were analyzed to measure their available phosphorous. 20 paddy fields over 100 paddy fields of each province were selected in a pattern that satisfy good geographical distribution and available phosphorous as: less than 6, 6-10, 10-14, 14- 18, and more than 18 mg kg-1. Enough surface soils were collected from each selected paddy field. Surface soils air-dried and were similarly transferred into experimental plastic pots with a diameter of 28 and depth of 40 cm. Each sample was treated with two treatmentsT1: without P application, and T2: application of 100 mg P2O5 per kg of soil from triple superphosphate source, in three replications as a randomized completely block design. Paddling of soils were performed inside of pots ,followed by digging of pots into the field up to plow soil.3 to 5 seedlings of selected rice varieties for each region, were transplanted in the center of experimental pot. At the maturity stage, rice plant was harvested from the first node above the ground to measure the straw and grain yield based on 14% moisture content. The relative yield was calculated for each treatment, and P critical level was determined for each province by use of graphical Cate-Nelson method. The results have shown that effects of P fertilizer application on the grain yield, total dry matter and plant height was significant in Khuzestan. The P critical level based on 90% relative yield was determined 10 to 14 mg kg-1 for Khuzestan paddy fields. The results obtained from Chaharmahal va Bakhtiari have shown none significant effect of P application on grain yield, total dry matter and P concentration of grain, but a significant effect on straw weight, harvest index and p concentration of shoot. The soil P critical level for Chaharmahal va Bakhtiari paddy fields was determined as 13 mg kg-1, based on 90% relative yield.
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