The Effect Of Mulch On Soil Properties And Plum Tree Growth And Development In Mountainous Orchard

Plum (P.salicina Lindl.)is a kind of plant belongs to Prunus L.of Rosaceae, which is a perfect season fruit and raw material for processing natural healthy food. Chongqing is the tranditional growing area, but the solid climate condition is not so good,which debases plum fruit quality. Mulch is a effective and simple method to solve this problem. Up to now, there have no publicated reports on the effect of mulch on soil properties and plum tree growth and development.By the combined method of field investigation and laboratory analysis, Prunus salicina Lindl.cv.Qingcui was taken as trial material to study the effect of mulch on soil properties and tree growth and development in mountainous plum orchard.The results showed that in hot and dry season,the straw mulch and plastic film coverage had increased water contents of various soil layers in orchard by different degrees and efficiently prevented water from vaporization, as well as made the most rainfall water infiltrate into soil to increase the water content.Especially, the straw mulch had the best effect with the water content increase by 30.9%-39.6% in top soil layer and 26.7%-38.2% in 20cm deep soil layer.The plastic film coverage had less effect with the water content increase by 20.9%-31.73% in top soil layer and 16.3%-28.1% in 20cm deep soil layer.This indicates that mulch can help improve soil water distribution and increase soil water content rate as well as available water content, which in turn increase the plant absorbability to water.This mulch effect has an important significance in preventing from short period drought.The straw mulch could obviously reduce extreme temperature on top soil in all seasons by 6.1℃-12.2℃, especially by 12.2℃in summer and by 10.5℃in autumn, as well as by 6.1℃in winter and by 6.9℃in spring.As the soil layer deepened, the effect of temperature reduction weakened.The plastic film coverage increased the extreme temperature in top soil with an obvious increase by 4.8℃in winter and by 6.9℃in spring, as soil layer deepened, the effect of temperature increase weakened.Mulch can increase soil humus content, promote the formation of soil aggregate structure, relatively reduce the bulk density of soil and increase the total soil porosity,.By straw mulch, the bulk density of soil was 1.02 g/cm~3, total soil porosity was 59.8%, consistency was 1.17 kg/cm~3, and by plastic coverage, the bulk density of soil was 1.15 g/cm~3, total soil porosity was 48.5%, consistency was 1.46kg/cm~3. All the figures are significantly different from the ones by control. Mulch treatments also improved the soil structure and increase the level of N, P,K and organic material in soil. Under straw mulch, the level of N, P,K and organic material were 66.41mg/kg,40.27mg/kg,131.26mg/kg and 3.08% separately, while under plastic film coverage, those were 66.41mg/kg,40.27mg/kg,131.26mg/kg and 3.08% separately. Mulch enhanced the root system which reached to 152pcs /m~2, especially the fibre root system which reached to 107pcs/m2, in top soil and strengthened root vigor.By observation on the numbers of cellulose-decomposing bacteria and silicate bacteria in soils treated by different mulch methods,it was found that there were significant different between the numbers of these two bacteria types. And their numbers had showed the seasonal change trend which decreased in gradation of summer,autumn,spring and winter.The seasonal pattern of soil enzyme activities was nearly the same as the one of soil microrganisms.Under different mulch treatments,soil enzyme activities were stronger in summer and autumn and weaker in spring and winter.Straw mulch also increased single leaf area by 20.34%, thickness by 21.79% as well as chlorophyll content by 32.35%, while plastic film increased single leaf area by 4.98%, thickness by 8.37% as well as chlorophyll content by 11.27%, which enhanced photosynthesis and tree growth. Meanwhile, straw mulch and plastic film greatly increased the contents of N by 14.6% and 5.8%, P by 33.3% and 11.1%, K by 23.2% and 7.9% as well as other mineral elements in leaves with a improvement of tree nutrition.The mulch treatments had positive influence on the growth of plum fruits.The straw mulch could obviously enhance fruit enlargement, with an increase of fruit diameter by 7.5% in comparison with control in the mature stage. Straw mulch made the highest yield per tree which was 72.7kg, average fruit weight which was 20.5g and fruit set rate which was28%,with a improvement of fruit quality. Straw mulch and plastic film coverage significantly promoted total soluble solids by 16.33% and 11.22%, total sugar by 17.67% and 13.52% and monosackcharide by 16.74% and 27.24% in fruits.