Phosphorus fertilizing potential of bagasse ash and rice husk ash in wheat–rice system on alkaline loamy sand soil

SUMMARYBagasse and rice husk are two important agro-industrial by-products that are used as fuel in the sugar and rice mill industries, thus producing large quantities of bagasse ash (BA; 0·05 of bagasse) and rice husk ash (0·20 of rice husk) as waste material. Applying BA and rice husk ash (RHA) to agricultural land improves yield, nutrient uptake and chemical fertility of soil, particularly with special reference to available phosphorus (P) and potassium (K). The present field experiment was conducted for 3 years to evaluate the P fertilizer value of these agro-industrial waste materials in a wheat–rice system (WRS). The experiment was laid out in a split-plot design with RHA and BA applied at 10 t/ha and including a no-amendment control as the main plot treatments and three levels of fertilizer P (0, 13 and 26 kg P/ha; designated P0, P13and P26, respectively) as sub-plot treatments to wheat in WRS. Application of fertilizer P increased the wheat grain yield up to P26in the un-amended control treatment. However, a significant response of wheat to fertilizer P was also observed up to P13in the presence of BA and RHA, thereby saving 50% of fertilizer P. Both RHA and BA increased wheat productivity by 12 and 16%, respectively, over the un-amended control. The subsequent rice crop also produced 14% higher paddy yield when the two ashes were applied along with P13to the previous wheat crop. The increases in grain yield were accompanied by significant increases in the uptake of P and K, and P content (Olsen P) in the soil. The application of recommended P (P26) in un-amended plots resulted in a negative P balance of 9·3 kg P/ha/year. On the other hand, the application of BA alone and RHA along with P13resulted in neutral/slightly positive P balance. A strong linear relationship (R2= 0·98) was observed between P balance and Olsen-P build up in the soil. It may be concluded that application of BA and RHA has the potential to increase system productivity and reduce the cost of inputs in terms of reduced application of fertilizer P to wheat and rice.