EFFECT OF ORGANIC AND INORGANIC FERTILIZERS ON AZOTOBACTER AND CYANOBACTERIAL POPULATION AND RICE CROP IN PIEDMONT SOIL

Abstract

A study was undertaken to evaluate the combined effects of organic and inorganic fertilizers on the indigenous Azotobacter and cyanobacterial population in soil and on the growth and yield of rice for the Boro-fallow-T. aman rice cropping pattern. The study was carried out both at the field and the laboratory of the Department of Soil Science, Hajee Mohammad Danesh Science and Technology University, Dinajpur. In the field experiment, BRRI dhan28 (boro) and Kataribhog (aman) were grown following the rice-rice cropping pattern in the two consecutive years of 2009 and 2010 in Piedmont soil (AEZ#1). The study was initiated in November 2008 and was continued up to January 2011 to complete two crop cycles with boro rice (BRRI dhan28) as the first crop and T. aman rice (Kataribhog) as the second crop in each cycle. The experiment was laid out in the randomized complete block design (RCBD) with eleven treatments having three replications. The 11 treatment combinations consisting of N, P, K, S, Zn, cowdung (CD), poultry manure (PM) and mustard oil cake (MOC) including one control treatment were as follows- T0 : Control, T1 : 100 % RFD on the soil test basis, T2 : 75% RFD+25% CD, T3 : 50% RFD+50% CD, T4 : 75% RFD+25% PM, T5 : 50% RFD+50% PM, T6 : 75% RFD+25% MOC, T7 : 50% RFD+50% MOC, T8 : 75% RFD+25 % (CD, PM, MOC), T9 : 50% RFD+50% (CD, PM, MOC) and T10 : 34% CD + 33% PM + 33% MOC. Data were recorded on yields, yield components and N, P, K and S contents and uptake by the grain and straw of rice. In the laboratory indigenous cyanobacterial and Azotobacter population in soil under study were determined before transplantation, 30 and 60 days after transplanting (DAT) and after harvest of rice crops. Soil organic matter status, total N, available P, S and exchangeable K of soil were also determined at 30 and 60 DAT and after harvest of rice crop to assess the nutrient dynamics due to impose of different treatments. The results of the present investigation indicated that integration of organic and inorganic fertilizers significantly influenced the yield and yield components of rice, indigenous cyanobacterial and Azotobacter population in soil and soil chemical properties. Results showed that the highest grain yields of boro rice of 6.09 and 5.75 and those of straw of 6.86 and 7.65 t ha-1 were recorded in treatment T8 having 75% chemical fertilizer and 25% organic manures during boro seasons of 2009 and 2010, respectively. The lowest grain yields of 3.15 and 2.82 and those of straw yields of 3.88 and 3.37t ha-1 were recorded in T1 during 2009 and 2010, respectively. The highest grain yields of T. aman rice of 5.40 and 4.90 and those of straw yields of 10.21 and 11.21t ha-1 were recorded in T8 during T. aman seasons of 2009 and 2010 respectively. The lowest grain yields of T. aman rice of 2.78 and 2.28 and those of straw yields of 4.67 and 5.67t ha-1 were found in T1 during 2009 and 2010, respectively. The yield components viz. plant height, tillers hill-1, panicle length, grains panicle-1 and 1000 grain weight were significantly affected by the treatments and the maximum values were recorded in treatment T8. The highest N, P, K and S contents and uptake by rice were recorded in treatment T8. Cyanobacterial and Azotobacter population was significantly affected by the treatments. Higher cyanobacterial population was recorded in 2010 than those were observed in 2009. On the contrary, cyanobacterial population was higher in boro season than those were recorded in T. aman season of the same year. Similar pattern of Azotobacter popular was recorded during the entire period but the population was higher in boro season than those of T. aman season. Soil organic matter and nutrient status such as total N, available P, S and exchangeable K were slightly increased due to experimentation. From the overall results, it can be concluded that integration of organic and inorganic fertilizers can save 25% chemical fertilizer without any yield decline.