Effect of nitrogen fertilizer rates and mepiquat chloride application on lodging resistance indices and grain yield of rice (Oryza sativa L.cv. Hashemi)

Rice is a valuable and strategic cereal that plays an important role in providing food security for more than 50% of the world's population. New rice production systems require stable management operations. The role of nitrogen as a key determining factor is necessary to achieve optimal yield. As a synthtic growth regulator, mepiquat chloride is one of the important management tools in reducing stress damage and overcoming many agricultural problems, such as lodging. Mepiquat chloride reduces the distance between nodes in the main stem and tillers. The objective of this experiment was to investigate the effect of nitrogen fertilizer and mepiquat chloride on yield, yield components and lodging resistance indicators in rice.

To investigate the effect of nitrogen fertilizer rates and the foliar application of the growth retardant mepiquat chloride on lodging resistance and grain yield of rice cv. Hashemi, a factorial experiment based on a randomized complete block design with three replications was carried out during the spring of 2020 in the experimental field of Agriculture and Natural Resources Research Center in the village of Keshel Varzal in Rasht County, Guilan province, Iran. The experimental treatments included mepiquat chloride at four levels (no foliar application, and foliar application at the maximum tillering stage, stem elongation stage, and maximum tillering + stem elongation stages) and  nitrogen (N) fertilizer at three levels (13 kg.ha-1, 32.5 kg.ha-1, and 52 kg.ha-1). The studied traits also included the morphological characteristics (bending moment of internodes) related to the third and fourth internodes lodging, breaking resistance at the middle point of third and fourth internodes and lodging index, grain yield, number of panicles per plant, total number of grains per panicle, number of filled and unfilled grains per panicle and 1000-grain weight.
Research

The results showed that the highest grain yield (3999 kg.ha-1) was obtained from the foliar application of mepiquat chloride at the maximum tillering stage along with the application of 52 kg.ha-1 N and the lowest (2169.6 kg.ha-1) from no foliar application along with the application of 13 kg.ha-1 N. The maximum number of panicles per plant, number of total grains and filled grains per panicle were recorded in the mepiquat chloride foliar treatment at the maximum tillering stage and the application of 52 kg.ha-1 N. The lowest number of panicles per plant (and the number of filled grains per panicle) was obtained in the treatment of mepiquat chloride foliar application in the treatment of stem elongation and application of 13 kg.ha-1 N. The highest bending momentum of the third and fourth internodes (1563 and 1663.9 g.cm-1, respectively) was related to the foliar application of mepiquat chloride at the maximum tillering stage. Among the N fertilizer levels, the highest bending momentum of the third and fourth internodes (1521.1 and 1581.6 g.cm-1, respectively) were obtained from the application of 32.5 kg.ha-1 nitrogen.

Application of growth regulators and optimal use of nitrogen fertilizer are ways to prevent decline in rice grain yield. Foliar application of plant growth regulators and nitrogen chemical fertilizer on the plant characteristics of rice can help to improve resistance to plant lodging. According to the results of this experiment, it seems that foliar application of mepiquat chloride at the stage of maximum tillering and consumption of 52 kg.ha-1 nitrogen is the most suitable treatment for Hashemi rice cultivar in terms of increasing grain yield and resistance to plant lodging in climatic conditions of Rasht.