The Changes Of Weed, Temperature And Water Content In Soil Under Condition Of Conservation Tillage In Northwest Of Hebei Province

Ba-shang, the northwest part of Hebei Province locates in jigsaw-pattern zone containing agriculture and pasture. Where the plants are destroyed by over-pasturing and plowing. Serious problem of soil erosion and drought are limiting factors of crop production. Adoption of conservation tillage will alleviate above problem. Field experiments were conducted in Guyuan County. It was the first time to study conservation tillage under such environment. Several main crops in the region, corn, wheat, naked oat and flax, were planted. The research included comparison of soil water content and soil temperature under two tillage systems, weeds occur and weeds control in conservation tillage system, previous crops and crop yields. The results of the study were showed in the followings.1 36 weed species were found in weed investigation, included 17 annual weeds, 2 biannual weeds and 17 perennial weeds. Weed emergence centered around two stages. The first stage, from Apr 28 to May 14, is relatively lower temperature stage with air temperature maintained 10℃ or so. In this stage, perennial weeds and biannual weeds account for the majority of emerging weeds. The second stage, from May 15 to Jun 10, is relatively higher temperature stage with air temperature maintained 12℃ to 14℃. In this stage, perennial weeds and annual weeds composed the majority. From the two stages of weed emergence, the optimum timing of herbicide application can be draw.2 When residue cover maintained at 1.62t/hm2, soil temperature of conservation tillage was lower than conventional tillage all the time. The difference of soil temperature under two tillage systems can be divided into two stages. During the first stage, from Apr 20 to Jun 4, i.e. 35 days after planting of corn, soil temperature decreased 2.1℃. During the second stage ,from Jun 6 to July 9, soil temperature decreased 0.7℃. From Apr20 to July20, soil water content of conservation tillage was higher than conventional tillage in all the time with 0.85% increased in 0-10cm depth of soil, 0.93% in 10-20cm, 2.94% in 20-30cm and 4.09% in 30-60cm. There was no significant difference between two tillage systems in com development and growth. Low temperature of conservation tillage in early stage would not make serious problem in com production.3 Crop yield in two tillage systems and four different previous crops was analyzed. Crop yield of wheat, naked oat and flax in conservation tillage increased compared with that of conventional tillage. No-till corn was a favorable previous crop to wheat and naked oat No-till wheat was a favorable previous crop to naked oat and flax. Therefore, optimum rotation sequence for two crops was corn-wheat, corn-naked oat, wheat-flax and naked oat-flax, and for three crops was com- wheat-flax and corn-naked oat-flax.