RAINFALL INFILTRATION AND RUNOFF FROM AN ALFISOL IN SEMIARID TROPICALINDIA - II - TILLED SYSTEMS

Formation of low permeable crusts on Alfisols of semi-arid tropical In dia significantly affects runoff and erosion processes during rainstor ms. The management options commonly used to reduce runoff are tillage and/or application of organic amendments. Daily runoff data from a fie ld experiment conducted at International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, India, were analyzed to quantify the benefits of two different types of tillages (shallow tillage to a dep th of 10 cm and deep tillage to a depth of 20 cm) and application of a mendments (farmyard manure at 15 Mg ha(-1)yr(-1) and rice straw (Oryza sativa) at 5 Mg ha(-1)yr(-1)) using a no-till, unamended system as a control. The no-till system is discussed in detail in Part I. Runoff f rom tilled plots declined sharply after tillage operation and reverted back to that from an untilled plot after a few storms totalling about 150 mm of rainfall. Consequently, the effective period of tillage var ied from 5 days in 1989, when a single storm of 115 mm rain occurred 5 days after tillage, to about 60 days during 1993 and 1994. Quantitati ve rainfall-runoff relationships were developed by dividing 633 rainfa ll-runoff events over 6 years into three groups, depending on time of occurrence: fallow period, from time of tillage operation to receipt o f 150 mm of rain, and the remaining events during the cropping period after 150 mm of rain to crop harvest. More than 73% of the variation i n runoff from bare and farmyard manure plots could be explained by eit her rainfall amount or by the product of rainfall amount and 30 min in tensity. In addition, soil cover was important during the fallow perio d. Using the 5 min rainfall intensities, we found that runoff of tille d systems may be reduced from 35% to 10% of rainfall by adding straw. The implication is that organic amendments (such as straw or farmyard manure, if available) offer a sustainable way for Alfisols to maintain a high infiltration rate and, thereby, both reduce runoff and increas e the amount of water available for crop production. (C) 1998 Elsevier Science B.V. All rights reserved.