Ridge tillage and contour natural grass barrier strips reduce tillage erosion

Large amounts of soil are eroded annually from tilled, hilly upland soils i n the humid tropics. Awareness has been increasing that much of this erosio n may be due to tillage operations rather than water-induced soil movement. This field study estimated soil translocation and tillage erosion for four tillage systems on Oxisols with slope gradients of 16-22% at Claveria, Mis amis Oriental, Philippines. Soil movement was estimated using 'soil movemen t tracers' (SMT) which consisted of painted 12-mm hexagonal steel nuts. The SMT were buried in three replicate plots of the following tillage treatmen ts: (1) contour moldboard plowing in the open field (MP-open); (2) contour ridge tillage in the open field (RT-open); (3) contour moldboard plowing pl us contour natural grass barrier strips (MP-strip); and (4) contour natural grass barrier strips plus ridge tillage (RT-strip). Two hundred SMT were p laced at the 5-cm depth at 5-cm spacings on 10 rows and 20 columns in two m icroplots within each plot. The microplots were oriented with the boundarie s running downslope and along the contour of each 8-m-wide x 38-m-long (dow nslope) tillage plot. After tilling the land for four successive corn (Zea mays L.) crops (20 tillage operations), the SMT were manually excavated and their positions recorded. Recovery of SMT ranged from 82% to 85%. Displace ment of SMT was directly related to slope length, percent slope, and tillag e method. Mean displacement distance of SMT during the four corn growing se asons was 3.3 m for MP-open, 1.8 m for RT-open, 1.5 m for the RT-strip, and 2.2 m for MP-strip. Based on tillage operations associated with two corn c rops per year, mean annual soil flux was estimated to be 241, 131, 158 and 112 kg m(-1) for MP-open, RT-open MP-strip, and RT-strip, respectively. Com pared to the mean annual soil loss for MP-open of 63 Mg ha(-1), soil loss w as reduced by 30%, 45%, and 53% for the MP-strip, RT-open, and RT-strip sys tems, respectively. Both ridge tillage and natural grass barrier strips red uced soil displacement, soil translocation flux, and tillage erosion rates. (C) 1999 Elsevier Science B.V. All rights reserved.