Effect of cultivar, rates, and time of nitrogen fertilizer Application on yield and yield components of lowland irrigated rice (Oryza sativa l)

Dissertation

Nitrogen (N) is one of the major elements required by rice (Qryza saliva L) plants for growth and development. Nitrogen deficiency in rice is caused by losses of the element from the soil- plant system, mainly through denitrification, ammonia volatilization, leaching and runoff. Thus, careful management of N both in terms of rates and timing of application is essential in order to improve its utilization by the plants. An experiment was therefore conducted at Mkindo irrigation project in Mvomero district, Tanzania to evaluate the response of three rice varieties to different rates and times of N application. A split-split plot design with three replications was adopted. The main plots contained three rice varieties (TXD85, TXD306 and Supa). The sub- plots contained four rates ofN (0,40,80,and 120 kg N ha'1) while the sub-sub plot represented four times of N application (Tl=single dose in dry' soil before transplanting, T2=two equal splits: half dose each in dry soil before transplanting and at initial tillering, T3=three equal splits: one- third dose each in dry soil before transplanting, initial tillering and panicle initiation, T4=two equal splits: half dose each at initial tillering and panicle initiation). Dry' mass accumulation varied significantly (P<0.05) among treatments. Highest dry' mass accumulation was recorded in TXD 306 and the lowest in Supa. More dry' mass was attained with 120 kg N ha-1 applied as T4 and the lowest without N. Application of N as T4 gave the highest dry' mass, while the low'est with N as Tl. Grain yield increased significantly (P<0.05) with increasing N rates in cultivars TXD 85 and TXD 306 up to 120 kg ha' The yield increase in Supa w'as only up to 80 kg N ha'1 after which it declined. Time of N application significantly (P<0.05) affected grain yield in rice with highest Ill results suggest that grain yield increased proportionately with increased N availability in the soil. Grain yield variation among treatments was found to be associated with variations in the number of panicles/m2, panicle weight and number of grains/panicle. Among growth parameters, grain yield w'as significantly (P<0.01) influenced by grain dry mass, stem dry' mass, and total dry mass. Leaf dry' mass had no direct contribution to the observed variation in grain yield. Nitrogen use efficiency (NUE) varied among treatments. TXD 306 recorded highest NUE and low'est in Supa. Highest NUE w'as realized with low N rates (40 w'as therefore concluded that, economic optimum N rate for TXD 85 and TXD306 was 120 and 80 kg N ha’1, respectively, applied as T4 while for Supa was 40 kg N ha'1 applied as T4.