Effect of different types of crop residue mulch on the emergence and early growth of safflower and wheat under different moisture levels

Introduction Drought and water shortage are the most important limiting factors in agricultural production, and environmental stresses are considered as the most serious threats for seed germination and crop growth. Researchers have mentioned crop residue management as one of the methods to improve soil physical properties, reduce evaporation intensity and protect the environment against global warming. Crop residue also contains a lot of organic matter which has a high water holding capacity, thus the addition of plant residue to soil could result in an effective increase in soil water holding capacity. With regard to importance of soil and water conservation, proper crop residue management plays important role in crop production in arid and semi-arid regions. According to a special role of crop residue in maintaining soil moisture and increasingly spreading of drought stress in the country, this research examines the impact of crops residues and on the emergence and early growth of safflower and wheat crops under different moisture levels. Materials and Methods To study the effect of different levels of moisture and the type of crop residues on germination and early growth of safflower and wheat crops, separate experiments for each plant were conducted in the greenhouse of Faculty of Agriculture, University of Birjand. For this purpose, a factorial experiment for each crop was conducted in a CRD with three replications that contained three levels of moisture (25, 50 and 80% of water holding capacity of the pot) and 5 types of crop residues (chickling pea, rocket salad, triticale, barley and control (no residue on the surface of the pot)). During the trial, number of emerged seedlings was recorded and cumulative rate of seedling emergence was calculated. At the end of the study, the seedlings height was measured and plant from surface of the soil were harvested. After measuring the leaf area of plants, their dry weight were measured. Result and Discussion Results showed that the final percentage of seedling emergence and height of wheat at moisture levels of 50 and 80% of field capacity were not significantly different while these traits significantly decreased in moisture level of 25% field capacity. Wheat plant height was significantly increased just with residues of chickling pea compared to control. Results of interaction effect showed that in general, in moisture levels of 50 and 80% of field capacity, the cumulative rate of seedling emergence of wheat in different treatments of crops residues had no significant difference with the control. However, at 25% of field capacity, cumulative rate of seedling emergence of wheat was greater than the control at all levels of cover crops residues. This result suggests that under low moisture levels, the presence of residue of cover crops on the soil surface can improve emergence rate, probably due to more moisture maintenance in the soil surface by residue of cover crops. Results for safflower showed that cumulative rate and final percentage of emergence of safflower in all types of crops residues decreased compared to the control. It seems that plant residues have inhibitory effect on safflower emergence. Previous reports have also confirmed that when the crop residue are on the soil surface, emergence of some plants, especially broad-leaved species like safflower, delay, because of the physical barrier that prevents the growth of seedling plumule to the soil surface, while narrow-leaved plants easily pass through plant residues and plant residues do not prevent their emergence. Moreover, in the treatment of 80% of field capacity, the dry weight of safflower in crop residue treatments of chickling pea, rocket sativa, and triticale increased compared to the control and the greatest dry weight of safflower was observed with the chickling pea residues. In the treatment of 50% of field capacity, dry weight of safflower in all treatments of crops residues were greater than the control and in the treatment of 25% of field capacity, dry weight of safflower were greater in chickling pea and rocket sativa residues compared to the control. Crop residues increase soil moisture content through enhancing the soil organic carbon, as well as reducing run off and evaporation in surface soil. More water content and reduced evaporation caused by the residue mulch are the main reasons for the increase of germination, emergence and seedling growth. (Malhi et al., 2006). Conclusion The results showed that the crop residue had a positive impact on the growth of the safflower and wheat under drought stress. Crop residue of chickling pea, especially under stress conditions had a positive impact on growth characteristics of safflower and wheat. Therefore, the use of crop residue can be a useful way to increase the usable moisture in arid and semi-arid regions.