Promotive and inhibitory effects of rice straw and cellulose application on rice plant growth in pot and field experiments

In a pot experiment, rice straw and cellulose were applied at the rates of 0.2 and 0.5% on a dry soil weight basis with two different incubation periods (2 months and 3 months) from their incorporation to rice transplanting. Seven treatments were designed as follows, T1, control; T2, straw 0.2%; T3, straw 0.5%; T4, cellulose 0.2%; T5, cellulose 0.5%; T6, straw 0.2%+inorganic N fertilizer; and T7, cellulose 0.2%+inorganic N fertilizer. T6 and T7 contained 58 mg N pot(-1) of ammonium chloride (approximately 10 kg N ha(-1)) in addition to straw and cellulose, respectively. Promotive and inhibitory effects of straw and cellulose application were observed and both were closely related to the incubation period. Straw application at 0.5% increased plant dry matter yield and N uptake compared to T1 and the promotive effect was more appreciable in the 3-month-incubation period than in the 2-month one (hereafter referred to as 3i and 2i, respectively). Cellulose application at 0.5% inhibited rice plant growth and the inhibitory effect was more severe in 2i than in 3i. The concentration of volatile fatty acids (VFA) in paddy soil was very low or VFA were not detectable after 2 months of incubation in all the treatments. In the field experiment, rice straw and cellulose were applied at the rates of 4 and 10 t ha(-1), which corresponded to 0.2 and 0.5% on a dry soil basis, respectively, under subtropical climate conditions. There were five treatments which were equivalent to T1 to T5 described above. Straw was applied 3 times continuously before the three rice cultivations, whereas cellulose was applied 2 times before the first and second cultivations. In the first cultivation, straw application at 10 t ha(-1) increased straw and total dry matter yields compared with the control. In the second cultivation, straw application at 10 t ha(-1) increased grain and total dry matter yields, whereas cellulose application retarded plant growth severely. Straw application at 10 t ha(-1) tended to enhance the grain/straw ratio compared with the control in the second and third cultivations.