Study of root traits of forage maize (Zea mays L.) in different tillage systems, drought stress, and nitrogen fertilizer

The first factor limiting plant yield in many crop ecosystems is drought stress, and plant productivity under these conditions depends on the distribution of dry matter between plant organs and the spatial distribution of roots in the soil. Knowledge of root length conditions and its distribution in soil profile, which is an indicator of the ability of plants to absorb water from deeper layers and better root permeability in the soil, as well as understanding the shape of the root system, is important (Wasson et al., 2012). In general, the size, morphology, and architecture of the root system determine the plant's ability to absorb water and nutrients, as well as the relative size and growth rate of the shoot (Vamerali et al., 2003). Root growth is determined by the genetic characteristics of the plant as well as the physical and chemical characteristics of the soil. Even in wet areas in response to drought stress, root growth is limited to the topsoil, and when the soil dries, its infiltration resistance increases rapidly, resulting in a combination of drought stresses. Soil and its infiltration resistance (He et al., 2017). Reduction of root dry weight in rice (Nasiri et al., 2015), fresh weight of root in rapeseed (Razaviezadeh and Amoubeigi, 2013) indicate the negative effect of drought stress on root characteristics in Different plants. Tillage is the only crop method by which humans can directly affect soil properties. Moisture storage and aeration to the roots, depending on the desired or unfavorable application of tillage, affects the growth and development of plant roots and ultimately its yield (Bronick and Lal, 2005).

This experiment was conducted in split -split plots based on randomized complete block design with three replications. Tillage systems as the main -plot in two factors was including no tillage and conventional tillage, Water stress as the subplot in three levels by 30, 60 and 90 Percent of moisture requirement and nitrogen urea as the sub-sub plot at three levels by 0, 50 and 100 percent of the recommended rate.

The combined variance analyses indicated that the maximum root length (4147 cm per plant), root volume (158.13 cm3 per plant), root area (3055.7 cm2 per plant), root length density (0.44 cm2. cm-3), root dry weight (24.32 gr pl-1) and plant fresh weight (6732.6 gr. m-2) was obtained from the interaction of conventional tillage in mild drought stress (90% of the plant's water requirement) in 100% of the plant's nitrogen fertilizer requirement. Also, the interaction effect of severe drought stress (30% of plant water requirement) in 100% of plant nitrogen fertilizer requirement led to a sharp decrease in studied traits in both studied tillage systems. Although the conventional tillage system in this study ultimately increased the root growth characteristics and fresh weight of the forage maize plant, but because no significant difference in wet forage yield was observed in both studied tillage systems, the system no tillage is recommended because it can improve the physical and chemical properties of the soil in the long turn.