Journal of Crop Production and Processing

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Sadeghi S A, Mobasser H R, Rahimi Petroudi E, Daneshmand A. Evaluation of Planting Depth and Plant Density Effects on Vegetative Traits, Yield, and Grain Quality of Shiroudi Rice (Oryza sativa L.) in the Amol Region, North of Iran. J Crop Prod Process. 2026; 16 (3) :79-98
URL: http://jcpp.iut.ac.ir/article-1-3403-en.html

Introduction: Rice (Oryza sativa L.) is one of the world’s most important food crops, and improving its yield and ensuring sustainable production are essential for global food security. Spatial variability caused by erosion or topographic features can alter soil properties across different cultivation zones. Selecting an appropriate planting depth enhances plant growth, root development, and yield, although the extent of these effects depends on soil type and field conditions. Determining the optimal plant density in rice cultivation is also crucial, as it is influenced by the soil’s physical and chemical characteristics as well as its fertility status. Accordingly, this study aimed to investigate how planting depth affects the optimal plant density of rice at two distinct locations in the Amol region in north of Iran.

Materials and Methods: This experiment was conducted in Amol, located in Mazandaran Province in northern Iran. A randomized complete block design with a split plot arrangement and four replications was used. Planting depth at two levels (1.5 and 4 cm) served as the main factor, while plant density at three levels (15.2, 19.6, and 27.8 hills m-2, corresponding to planting spacings of 22 × 30, 17 × 30, and 12 × 30 cm, respectively) was evaluated as the sub factor. The study was carried out simultaneously in 2022 and 2023 across two rice fields with different geographic coordinates (Location 1: 36°36'16.9"N, 52°28'10.9"E; Location 2: 36°36'25.4"N, 52°27'57.5"E) but under the same climatic conditions. Measured traits included root length, shoot height, number of panicles m-2, total spikelets m-2, filled spikelets m-2, 1000 grain weight, paddy yield, milling recovery, head rice yield, chalkiness, and gelatinization temperature. Combined analysis of variance was performed using SAS 9.2 and MSTAT C, and mean comparisons were conducted using Tukey’s test at the 5% probability level.

Results and Discussion: The results showed that at the tillering stage, root length in Location 2 was 8.7% greater than in Location 1. However, at the panicle initiation stage, shoot height in Location 1 exceeded that of Location 2 by 27.63 cm. At the tillering stage, root length at the 4 cm planting depth was also 7.2% shorter than at the 1.5 cm depth. During panicle initiation, the greatest root length was recorded in Location 1 at the 1.5 cm depth (25.74 cm). At the flowering stage, the highest root lengths (21.87 and 20.73 cm) and shoot heights (111.1 and 114.1 cm) were obtained in the same location at planting depths of 1.5 and 4 cm, respectively. In this stage, the minimum root length occurred at the density of 27.8 hills m-2 (19.12 cm), while the shortest shoot height in 2023 was observed at the density of 19.6 hills m-2 (100.2 cm). The lowest shoot height at the tillering stage was recorded in Location 1 in 2022 at the 4 cm depth and a density of 27.8 hills m-2 (27.84 cm). The highest total number of spikelets and filled spikelets m-2 was recorded in Location 1 at the density of 27.8 hills m-2 (73120 and 65300 spikelets, respectively). The maximum number of tillers m-2 in Location 1 was obtained in 2022 and 2023 at the 1.5 cm planting depth and the density of 27.8 hills m-2, with 541.1 and 549.5 tillers, respectively. In addition, the greatest 1000-grain weight was recorded in the same location and only in 2023 under the same treatments, reaching 28.59 g. The highest paddy yield, 9322 kg ha-1, was achieved in Location 1 in 2022 at the density of 15.2 hills m-2. Additionally, the maximum paddy yield in the latter location was obtained at the 1.5 cm planting 

depth with a density of 15.2 hills m-2 (9559 kg ha-1), and at the 4 cm depth with a density of 27.8 hills m-2 (9291 kg ha-1). The milling degree in Location 1 was 2.82% higher than in Location 2. However, gelatinization temperature (3.678) and grain chalkiness (4.326%) were both higher in Location 2 compared with Location 1 (3.142 and 3.836%, respectively). The milling degree in 2023 was also 1.75% greater than in 2022. In addition, the lowest milling degree was observed at the density of 19.6 hills m-2 (83.64%). The lowest milling recovery, with an average of 61.40%, occurred in Location 2 in 2022 at the density of 19.6 hills m-2.

Conclusions: Based on the results of the present study, root length was greater in Location 2 at the tillering stage; however, during panicle initiation and flowering, both root length and shoot height were superior in Location 1. In Location 1, the highest number of tillers, the greatest 1000-grain weight (under shallow planting), and the highest total and filled spikelets (under both shallow and deep planting) were obtained at a density of 27.8 hills m-2. In the same location, planting at 1.5 cm with 15.2 hills m-2 and 4 cm with 27.8 hills m-2 produced the highest grain yields. In 2022, the lowest milling recovery was recorded in Location 2 at a medium density of 19.6 hills m-2, and grain chalkiness was also higher in this location. Overall, for the Amol region and the clay-loam conditions of Location 1, planting at 1.5 cm with 15.2 hills m-2 and 4 cm with 27.8 hills m-2 is recommended for the Shiroudi cultivar.