Nitrogen Regulation Of Sandy Soil By Straw Modified Materials

Sandy soil with large particles and rare organic matter have many problems, such as soil particle dispersion, low soil nutrient content, weak retention of moisture and nutrient, and so on. These problems lead to lower soil productivity and water environment pollution caused by nutrients loss with water. So it is critical important to ameliorate sandy soil to improve its moisture and nutrient retention. We proceeded cultivation experiment, adsorption-desorption experiment and simulated soil column leaching experiment for investigating how different ratio, dosage and culture time of composite straw amelioration materials (including straw, bentonite and PAM) impact on mineral nitrogen content and characteristics of nitrogen's adsorption-desorption and eluviation. The main conclusions of research are:1.The contents of NH₄⁺-N and NO₃^--N in soils were affected obviously by dosage and culture time of composite straw amelioration materials but not PAM. Compared with CK, NH₄⁺-N content in the soil fertilized with 2g/kg,5g/kg and 10g/kg composite straw amelioration materials increased by an average of 7.98%,53.87% and 80.80% respectively, and the increase of NO₃^--N content were 30.19%,79.23% and 115.46%. NH₄⁺-N and NO₃^--N contents in soils showed an increasing trend with accretion of applied composite straw amelioration materials. NH₄⁺-N and NO₃^--N content increased in early cultivation (0-60d), reached maximum at 60d and then decreased by later time.2.The isothermal adsorption experiment indicated that NH₄⁺ adsorption of soil existed rapid and slow stages, the turning point varied with dosage of composite straw amelioration materials and ratio of PAM. Langmuir equation could well reflect NH₄⁺ adsorption reaction of soil, and correlation coefficients were highly significant. The results showed that:When culture time at 10d,30d, and 60d, NH₄⁺ saturation adsorption(Xm)of soil upgraded with increasing amount of composite straw amelioration materials; when culture time was 90d, Xm reached maximum while amount of composite straw amelioration materials at 5g/kg. When amount of composite straw amelioration materials invariable, the impact order of different PAM ratios on NH₄⁺ Xm in every period was PAM0.99%>PAM0>PAM1.96%>PAM2.91%. That meant low PAM ratio (0.99%) increased NH₄⁺ adsorption and upgrading PAM ratio could inhibit NH₄⁺ adsorption capacity. The effect of cultivation time on NH₄⁺ Xm varied with amount of composite straw amelioration materials:when the amount at 2 g/kg and 5g/kg, Xm declined during culture time; when the amount was 10g/kg, Xm reached maximum at 60d. Among all the treatments, Xm NH₄⁺ of that treated with T_10,1 was highest, increased from 243.90mg/kg (CK) to 1111.11 mg/kg.Composite straw amelioration materials posed opposite effect on NH₄⁺ adsorption capacity (K) and saturation adsorption (Xm) of soil. It indicated the application of composite straw amelioration materials and low ratio of PAM could improve NH₄⁺ adsorption capacity of soil but lower NH₄⁺ adsorption strength. It was worth to notice that NH₄⁺ adsorption strength of soil treated with 5g/kg increased significantly compared with CK and other treatments at 30d, reached significant level (p <0.05).3. The NH₄⁺-N desorption capacity of sandy soil increased after application of composite straw amelioration materials. The effect of PAM ratio on NH₄⁺-N desorption was not obvious and regular; but the NH₄⁺ desorption rate increased with accretion of composite straw amelioration materials. The result indicated that applying composite straw amelioration materials only elevated nitrogen adsorption amount in soil but not nitrogen-holding capability.4.The soil column leaching experiment showed that the concentration and cumulative leaching loss of NH₄⁺-N and NO₃^--N in eluviations of ameliorated sandy soil declined significantly comparing with CK and both declined with upgrade of composite straw amelioration materials. The application of composite straw amelioration materials restrained removal and leaching loss of NH₄⁺-N and NO₃^--N. While dosage of composite straw amelioration materials was invariable, the concentration and cumulative leaching loss of NH₄⁺-N and NO₃^--N reached minimum when PAM ratio at 0.99%. The results showed that when the amount at 10 g/kg, PAM ratio (0.99%)treatment was the best one with ultimate leachate loss of NH₄⁺-N and NO₃^--N in eluviations at 28.26%, 41.50% respectively.