Long-term effects of inorganic and organic fertilizer sources on yield and nutrient accumulation of lowland rice

Abstract

Deceleration in rice ( Oryza sativa L.) yield over time under fixed management conditions is a concern for countries like Bangladesh, where rice is the primary source of calories for the human population. Field experiments were conducted from 1990 to 1999 on a Chhiata clay loam soil (Hyperthermic Vertic Endoaquept) in Bangladesh, to determine the effect of different doses of chemical fertilizers alone or in combination with cow dung (CD) and rice husk ash (ash) on yield of lowland rice. Two rice crops—dry season rice (December–May) and wet season rice (July–November) were grown in each year. Six treatments—absolute control (T 1), one-third of recommended fertilizer doses (T 2), two-thirds of recommended fertilizer doses (T 3), full doses of recommended fertilizers (T 4), T 2+5 t CD and 2.5 t ash ha −1 (T 5) and T 3+5 t CD and 2.5 t ash ha −1 (T 6) were compared. The CD and ash were applied on dry season rice only. The 10-year mean grain yield of rice with T 1 was 5.33 t ha −1 per year, while the yield with T 2 was 6.86 t ha −1 per year. Increased fertilizer doses with T 3 increased the grain yield to 8.07 t ha −1 per year, while the application of recommended chemical fertilizer doses (T 4) gave 8.87 t ha −1 per year. The application of CD and ash (T 5 and T 6) increased rice yield by about 1 t ha −1 per year over that obtained with chemical fertilizer alone (T 2 and T 3, respectively). Over 10 years, the grain yield trend with the control plots was negative, but not significantly, both in the dry and wet seasons. Under T 3 through T 6, the yield trend was significantly positive in the dry season, but no significant trend was observed in the wet season. The treatments, which showed positive yield trend, also showed positive total P uptake trend. Positive yield trends were attributed to the increasing P supplying power of the soil.