Effect of the rate and application time of vermicompost on the yield and yield components of rice (Oryza sativa L. cv. Tarom Hashemi')

Biofertilizers, which are considered to be one of the principal components of sustainable agriculture in farming ecosystems, can significantly aid in the elimination or reduction of chemical inputs from farmlands (Sharma, 2002). Vermicompost can be used as a soil additive on farmland to decrease chemical fertilizers consumption due to being able to provide plants with nutrients, increase soil cation exchange capacity, and improve soil water holding capacity (Tejada and Gonzaler, 2009). Since there is limited information available on the effect of vermicomposts on rice yield, this research was performed to investigate the effects of rate and split application time of vermicompost on yield and some agronomic traits of Tarom Hashemi rice cultivar.
The experiment was carried out as split plot in a randomized complete block design with three replications in Amol in 2014-2015. The treatments included rates of vermicompost application in four levels (0, 5, 10 and 15 ton.ha-1) as main plot and vermicompost split application time in five levels (T1: 100% basal fertilizer, T2: 50% basal 50% tillering, T3: 50% basal 50%, T4: 50% tillering 50% heading and T5: 33.33% basal 33.33% tillering.33% heading) as sub plot. Pure nitrogen from urea source at the rate of 36 kg.ha-1 was uniformly split-applied throughout the experimental plots: 50% before prior to transplanting, 25% at the tillering and 25% at the heading. At the end of the season, some agronomic traits and grain yield were determined. Data analysis was done by using MSTAT-C software and means were compared using the LSD test at the probability level of 5%.
The results showed that the effect of different rates of vermicompost was significant on all the agronomic traits and grain yield. The effect of split application of vermicompost was significant on the measured traits except for the panicle length, 1000-grain weight and harvest index. Also, the interaction effect of the treatments was not found to be significant on the agronomic traits and grain yield. The greatest average grain yields (3790 and 3868 kg.ha-1) were obtained from vermicompost application rates of 10 and 15 ton.ha-1, respectively. Under the influence of vermicompost split application, the highest rice grain yield (3863 kg. ha-1) was achieved when vermicompost was split as 33.33% basal.33% tillering.33% heading and the lowest grain yield, decrease of 16% relative to T5 treatment, was associated with no split application of vermicompost (T1). It seems that if vermicomposting is applied in three splits, it can boost plant growth and consequently increase grain yield. This has been attributed to the role of vermicompost in improving soil structure and enhancing soil physical and biological properties, which, in turn, result in increased nutrient availability in the soil during different vegetative and reproductive stages of plant growth (Afsharmanesh et al., 2016). No application of vermicompost resulted in the lowest biological yield (5743 kg. ha-1). Increasing vermicompost rate to 10 and 15 ton.ha-1 raised rice biological yield by 26 and 27%, respectively. When vermicompost was split-applied, T5 treatment produced the highest biological yield (7630 kg. ha-1), which did not show any statistical difference with T4 treatment. T1 treatment gave the least biological yield, which was almost 14.3% lower than that of T5 treatment.
According to the results of our study, the application of 15 and 10 ton.ha-1 of vermicompost and application of vermicompst in three splits over the plant growth stages led to the increase of yield and yield components in rice. This indicates that using vermicompost as a complementary fertilizer along with chemical fertilizers, although might increase production cost for growers, it can to some extent reduce nitrogen fertilizers consumption, which will be an effective step in attaining sustainability in agriculture and preserving environment.