Response Of Integrated Soil Fertility And Carbon Sequestration To Continuous Entire Maize Stalk Returning Into Field In Loess Plateau

The experiment was conducted in maize breeding experimental site in Pingliang onLoess Plateau, under the condition of3,6and9years of continuous entire maize stalkreturinging into field, soil carbon sequestration, physical and chemical property, soilbioactivity, as well as maize growth and development characteristics were studied. Based onscientific evaluation of integrated soil fertility variation, the relationships among differentfactors were discussed to provide reference to soil fertility and carbon sequestrationimprovement. The main results are as follows:1. Under the condition of continuous all maize stalk returingin into field, plenty oforganic carbon input improved soil phical property. The proportion of>0.25mm Waterstable aggregate in0-40cm soil increased significantly. Treatment R0.25of H9increased34.6%compared with the control. Meanwhile, soil bulk density and porosity got improvedand solid-liquid-gas structure tended to reasonable. All these improvement promoted waterconservation and temperature modulation of soil. Moisture content at0-200cm showedH9>H6> H3>H0,11.2%,17.6%and23.8%increase in0-40cm soil saturate waterconductity were observed.2. Soil nutrients had active responses to continuous entire maize stalk returinging intofield. Total N, P alkaline hydrolytic N, available P and K at0-20cm soil increased.47%,17%and23%increment of TN, TP and available K were observed under H9treatment. Theeffectiveness of increasing fertility by stalk returining declined with the increasing soildepth.3. Continuous stalk returning resulted in remarkable increase of bacteria, fungi andactinomyce at0-30cm soil. Compared with the control, baceria increased87.4%,actinomyce increased63%and26%in fungi. Under the treatment of H9, Shannon-Winerindex and Pielous uniformity index reached0.64and0.42, increased19.3%and17.4%,respectively. Continuous stalk returning improved the activity of soil urease, Alkalinephosphatase, sucrose enzyme and Catalase effectively, showing H9>H6>H3>H0. Vegativegrowth changes into reproductive growth at silking stage, when the most prosperous growthoccurs, and also the highest activity level of soil enzyme.4. Milking stage is the crucial period for maize growth and grain formation, stalkreturning treatment had significant influence on maize photosynthesis at this stage. With the increasing time of treatment, net photosynthetic rate, transpiration rate and stomatalconductance improved, as well as Leaf area index and chlorophyll content. SOD, POD andCAT also increased. H9had393.52U·g-1FW of SOD, increased29.8%,32.73%and29.83%increment were also observed in POD and CAT, respectively. There is nosignificant difference among treatments.5. Significant difference was observed among different treatments in terms of maizegrain yield and total biomass, showing H9>H6>H3>H0. H9achieved17624.5kg.hm-2totalbiomass, increased12.3%,24.6%and35.4%compared with H6, H3and H0, respectively.Other factors such as crude ash, crude protein and fat were stable and there is no significantdifference. But6-19%difference was observed on ahlorophyll content, grain protein andsoluble sugar content. Root weight, density, total root legth and root activity at0-40cm soilwere increased under the treatment and reached the highest at silking satge. Then declined atmaturity, but the declination was delayed compared with the control.6. Stalk returning treatment significantly increased soil carbon sequestration andpotential. Organic carbon and carbon density at0-20cm soil showed H9>H6>H3>H0,compared with the control, SOC and DSOC of H9increased156%and188%, respectively.MBC, MBN and MBP of maize at each growth satge also increased under treatment.Average MBC of H9increased119.2%, indicating a significant effect of carbonaccumulation of soil microorganism.7. According to published comprehensive evaluation system of soil quality combined withthe experiment,12factors closely related to soil integrated fertility were selected forcomprehensive evaluation and weight estimates, including soil structure, nutrient supply,soil microorganism and maize growth and development. The evaluation model is: P=0.21X₁+0.11X₂+0.087X₃+0.064X4+0.029X₅+0.18X₆+0.066X₇+0.063X₈+0.042X₉+0.067X₁₀+0.061X₁₁+0.021X₁₂,where R0.25,organic carbon and grain yield had weight of0.21,0.11and0.18. The evaluation result showed H₉>H₆>H₃>H₀, coincidence with the reality.To sum up, for sterile farmland in Longdong Loess plateau, continuous maize stalkreturning into field could increase soil organic carbon, carbon density and soil aggregates,improve soil solid-liqued-gas structure, soil organic matter, TN, TP and microorganismfauna structure, as well as C, N P content of microorganism and keep a high and stable level.This would establish a soild base for plant growth and development, keep high and stableyield under succession cropping, and help to increase soil integrated fertility and productivity in Loess Plateau.