Basic Soil Productivity Of Spring Maize In Black Soil Under Long-term Fertilizations

Increasing basic farmland soil productivity has significance in reducing fertilizer application and maintaining high yield of crops. In this study, we defined that the basic soil productivity(BSP) is the production capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local environment and field management. Based on 22-yr(1990-2011) long-term experimental data on black soil(Typic hapludoll) in Gongzhuling, Jilin Province, and national monitoring station data on black soil in Northeast China,, the decision support system for an agro-technology transfer(DSSAT)-CERES-Maize model and Basic Soil Productivity Index(BSPI) model were applied to simulate the BSP of spring maize(Zea mays L.) to examine the effects of long-term fertilization on changes of BSP and explore the mechanisms of BSP increasing and main control factors. At the same time, the field and potting experiments were conducted to text and verified the simulated results. Five treatments were examined:(1) no-fertilization control(control);(2) chemical nitrogen, phosphorus, and potassium(NPK);(3) NPK plus farmyard manure(NPKM);(4) 1.5 time of NPKM(1.5NPKM) and(5) NPK plus straw(NPKS). The main results showed that:(1) Applying the calibrated DSSAT model well simulated yields by BSP of spring maize.The yields by BSP of spring maize under NPKM, 1.5NPKM, and NPKS showed a significant increasing trend, but not significant under both NPK with a 26.9% increase and the control with a 8.9% decrease over 20-years fertilization. The contribution percentage of BSP showed a significant rising trend(P<0.05) under 1.5NPKM. The average contribution percentage of BSP among fertilizations ranged from 74.4 to 84.7%, and ranked as 1.5NPKM>NPKM>NPK≈NPKS, indicating that organic manure combined with chemical fertilizers(1.5NPKM and NPKM) could more effectively increase BSP compared with the inorganic fertilizer application alone(NPK) in the black soil.(2) The simulated contribution percentage of BSP was close to measured value of field experiment. The normalized root mean square error(RMSE) and the index of agreement(d) were 5.39% and 0.74, respectively. Although the simulated values were higher than the measured values in potting experiment, the trend was the same that 1.5NPKM>NPKM>NPK>NPKS. The simulated values under the NPKM and 1.5NPKM were better than others and the errors rage was 8.3%.(3) Under the traditional fertilization, BSPI significantly increased during 1988 to 2006(P<0.01) and had a positive correlation with latitude. The BSPI increased with the latitude increasing. The trend was similar with the soil organic matter(SOM), total N and available N content.(4) SOM was the key factor in various nutrient factors that affecting BSP in black soil, and total N, total P and available P also play important role in BSP increasing.(5) The SOC content under NPKM and 1.5NPKM treatments significantly increased. However, there was a significant decreasing trend for SOC under no fertilizer control over 20 years. The SOC content decreased from 12.49 g kg-1 in 1990 to11.67 g kg-1 in 2008 with a decrease of 6.6%. The SOC stock in topsoil(0-20cm) increased 12.8%,41.5%、34.2% and 12.8% under the NPK, NPKM,1.5NPKM and NPKS, respectively, compared to the initial value, but decreased 6.2% under the control. There were high carbon sequestration rates under the treatments of NPKM and 1.5NPKM with values of 0.895 and 0.823 t C ha-1 yr-1, respectively. Although SOC stock also increased under NPK treatment, the carbon sequestration rate was only 0.218 t C ha-1 yr-1. Only the control treatment resulted in a significant decrease of SOC stock.(6) There was significant positive correlation between SOC content and yields by BSP of spring maize(P < 0.01), and yields by BSP of spring maize increased 220 kg ha-1 when SOC content increased 1 g kg-1. The SOC mineralization rate(yr-1) 0.14 in black soil. In order to maintain the balance of SOC, it must input 1.17 t C ha-1 yr-1.(7) The total nitrogen content under NPKM and 1.5NPKM treatments significantly increased. However, there was a significant decreasing trend for total nitrogen under NPK(20.7% decrease) and no fertilizer control(30.3% decrease) over 20 years. The available nitrogen contents were decreased 7.4%-15.0% under CK, NPK and NPKS treatments. It increased 11.4%-12.5% under chemical plus manure treatment. The average available nitrogen contents among fertilizations ranked as 1.5NPKM(149.06 mg kg-1)>NPKM(135.07 mg kg-1)>NPK(122.26 mg kg-1)>NPKS(114.56 mg kg-1)>CK(109.06 mg kg-1).(8) The C/N ration significantly increased under NPK(33.7% increase) and CK treatment(54.2% increase). The main reason is that the total nitrogen content decreased significantly while SOC content had not obvious changes. Because the SOC and total nitrogen contents both increased, the C/N ration under 1.5NPKM and NPKM increased 9.9% and 28.4%, respectively.(9) We recommend that a balanced chemical plus manure or straw fertilization(NPKM or NPKS) should be the fertilization practices to enhance spring maize yield and improve BSP in the black soil of Northeast China.