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 rate s of 0.2 and 0.5% on a dry soil weight basis with two different incuba tion 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%+inorg anic N fertilizer. T6 and T7 contained 58 mg N pot(-1) of ammonium chl oride (approximately 10 kg N ha(-1)) in addition to straw and cellulos e, respectively. Promotive and inhibitory effects of straw and cellulo se application were observed and both were closely related to the incu bation period. Straw application at 0.5% increased plant dry matter yi eld and N uptake compared to T1 and the promotive effect was more appr eciable in the 3-month-incubation period than in the 2-month one (here after referred to as 3i and 2i, respectively). Cellulose application a t 0.5% inhibited rice plant growth and the inhibitory effect was more severe in 2i than in 3i. The concentration of volatile fatty acids (VF A) in paddy soil was very low or VFA were not detectable after 2 month s of incubation in all the treatments. In the field experiment, rice s traw and cellulose were applied at the rates of 4 and 10 t ha(-1), whi ch corresponded to 0.2 and 0.5% on a dry soil basis, respectively, und er subtropical climate conditions. There were five treatments which we re equivalent to T1 to T5 described above. Straw was applied 3 times c ontinuously 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 tot al dry matter yields compared with the control. In the second cultivat ion, straw application at 10 t ha(-1) increased grain and total dry ma tter yields, whereas cellulose application retarded plant growth sever ely. Straw application at 10 t ha(-1) tended to enhance the grain/stra w ratio compared with the control in the second and third cultivations .