Soil loss study under different soil and water conservation measures for maize and redbean cultivation on steep land   Vasuthep Kanchanadul, Kittiporn Srisawas and Sawasdee Boonchee   ABSTRACT         Soil  loss study unde r different soil and water conservation measures for maize  and  redbean on steep land were  conducted on farmer  field at  Ban Sahakorn Mor 7, Tumbol Muangngai, Chiangdao district, Chiangmai  province during the year 1992 - 1994.  The experiment  was randomized complete block design with 5 treatments 4 replications. The following treatments  were maize relay with redbean on the contour, maize  relay  with redbean between trash  line, vetiver grass hedgerow,  leucaena mix with pigeonpea hedgerow and hillside ditches respe ctively.       The result of study  revealed that the treatments of maize relay with redbean between vetiver grass hedgerow, the  hillside  ditches  and  trash  line were  remarkably  reduced  the rate of soil loss to the minimum among the others treatment, it ranged from 631.3 and  551.7 kg/rai/yr, in three years average respectively. While the treatment of maize relay with redbean alone created the highest soil loss with 3 years average 1,001.3 kg/rai/yr. Similar trends and response were obtained with surface runoff. Runoff was highest under the relay cropping treatment alone and was reduced significantly on the treatment of relay cropping in associated with vetiver grass hedgerow and hillside ditches.      The result of the experiment also found that crop yields under relay cropping practice alone were declined over the years, whereas the opposite were happened in the treatments of relay cropping between trash line, vetiver grass hedgerow and alley cropping (leucaena mixed with pigeon pea double hedgerows) which were increasing both in crop yields and economical return, eventhough only 88.89% of the  land  area  was  cultivated.  This was probably due to better  crop  growth  resulting from the effective soil and water conservation and soil fertility  improvement  (returning of plant residue from vetiver grass, leucaena/pigeon pea and the trash line to the soil).       The chemical properties of the soil were affected by the different treatments and time, the pH and K were obviously decreased the top soil level for the reduction of soil pH, and the potassium in the plant were in the ion form, when plants were decomposed and leaching, potassium ion will be easily lost. The phosphorus was all increased.      The result from this study can serve as a good  guideline for soil conservation and  agricultural practices on the steep land, Li series and the similar soil types on the upper Northern area, that the treatments of relay cropping between leucaena mixed with pigeonpea hedgerow, vetiver grass and trash line can control soil erosion very efficiently as well as improve soil fertility, sustainable crop yields and economical return.         Keywords: Soil conservation.