Effect of burning wheat straw and stubble on water repellency and some soil properties in the fields of Dezful city

Background and objectives: Burning plant residues is one of the most common methods of agricultural land management, but the concern about its negative environmental consequences is spreading. The purpose of this research is to investigate the effect of burning wheat straw and stubble on soil water repellency and its temporal changes in soil properties.
Materials and methods: For this purpose, the remains and stubble left from the wheat fields were collected and placed on the surface of the field with a thickness of 0, 2, and 10 cm, and fire was carried out. Then, three times (24 hours, 10 and 30 days) after the fire, together with the Blank (before the fire), samples were taken from the 0-5 cm layer of the surface soil and some soil characteristics including soil pH, Electrical conductivity (EC), Organic matter (OM), abundance percentage of soil particles, permeability, soil water repellency were measured using molarity of ethanol droplet (MED) and water drop penetration time (WDPT). A total of 36 plots (4*3*3) were factorial designs implemented in a randomized complete block. In the WDPT method, by placing three drops of water with a medical dropper on the smooth surface of the soil, the duration of penetration and absorption of the drops by the soil was measured. To measure the amount of water infiltration into the soil, it was measured with three repetitions of the double cylinder test.
Results: Variance analysis of the effect of fire time on some soil characteristics of the studied area showed that fire affects the soil characteristics with a probability of 99% for electrical conductivity, soil pH, organic matter, sand, silt, clay, Mean Weight Diameter, phosphorus and Sodium. The results showed that after the fire, the amount of water infiltration into the soil decreased from 21.2 to 7.54 mm/h and electrical conductivity, soil reaction, phosphorus, potassium and absorbable, exchangeable sodium and silt were 29.50, respectively. 2.53, 169.84, 5.68, 9.79 and 10.48% increased and organic matter, sand, clay and MWD decreased by 16.09, 13.67, 7.11 and 45.8% respectively. The results showed that in terms of hydrophobicity, the soil of the region is in the Wettable class, after 24 hours after the fire, the WDPT reached 67.55 seconds and it turned into a soil with Slightly Water Repellency, so that with increasing depth, the number of residues and WDPT increased and reached its maximum of 67.79 seconds.
Conclusion: The burning of wheat residues in the fields of Dezful City increased soil nutrients including phosphorus, potassium, sodium and the relative percentage of silt compared to before the fire. After the fire and the increase in soil temperature, the hydrophobicity class of the soil changed from hydrophilic to low hydrophobicity. The results showed that the water repellency caused by fire depends on the duration of time after the fire so that it returns to a lower level with the passage of time and then its changes stop. Also, burning the residues decreased the permeability of the soil so that the permeability class changed from Very rapid to medium. Fire and burning of plant remain increase soil salinity and pH, which can be effective in reducing crop efficiency.