Effects Of Organic Amendments On Soil Fertility And Plant Growth

The improvement and management of soil fertility is not only the key to improve soilquality but also the core means of ensuring sustainable use of soil resources. It is alsosignificant to improve farm land productivity and ensure food security on regional or nationalscale. Both the domestic and foreign research showed that the most effective and meaningfulway for improving soil fertility is organic amendments among many soil fertilizationmeasures. Adding organic materials and planting cover (catch) crops have caused widespreadconcern. However, how to evaluate the effects of organic amendments through identifyingspecific measures and filtering key indexes of soil fertility according to local conditions thusestablishing highly-efficient fertilization mode still needs further research on regionalagriculture production. Because of this, two soils (typical dryland soil (Weibei arid loessplateau of China, Shaanxi) and humid region of northeast U.S.(State of Maryland)) ofdifferent climate types, soil properties and tillage managements, were selected to conductresearch on filtering and evaluating modes of adding organic materials and on effects ofplanting cover crops and so on. Through organic materials and optimized cropping system,theoretical basis concerning soil productivity improvement, efficient use of nutrient resourcesand eco-environment protection in dryland and humid regions can be provided. The resultsare as follows:(1) Compared to T1treatment, soil bulk desity under other organic fertilization treatmentsdeclined slightly, and it obtained the highest decrease (by6.56%) in T6treament. Organicamendments (low-, medium-, and high-level maize stalks, stalk composts, and cattle manure)combined with inorganic fertilization decreased the air-dried aggregate (>10mm and <0.25mm) content and increased53mm and1-0.5mm aggregate content. Meanwhile, organicamendments also increased>5mm,5–2mm and2–0.25mm water-stable aggregate content.The proportion of water-stable aggregates>5mm was the highest in T5treatment,6.5%,significantly higher than that in T1treatment, while those of52-mm increased remarkablywith organic amendments, with78.0%significant increase in T4treatment compared to T1treatment. Compared to T1treatment, T5treatment resulted in a greatest increase in meanweight diameter (MWD) and geometric mean diameter (GMD) of wet-aggregates by33.3%and24.7%respectively. (2) In the020cm soil layer, the POXC content was significantly higher in theorganically amended treatments than in T1treatment (P<0.05). Among the organicamendments, T6treatment showed a greatest increase by108.6%. Compared to NPKfertilization, the organically amended treatments increased the SOC content in most aggregatesize classes. The SOC content in0.50.25mm aggregates increased by12.8%significantly inT6treatment. Meanwhile, the POXC content in most aggregate size classes was alsosignificantly higher in the organically amended treatments. Among them, T5treatment showeda greatest increase by98.5%in1-0.5mm aggregates. There were significant positive relationsbetween the proportions of>0.25mm water-stable aggregates and POXC content (R2=0.625,P<0.05). In addition, the carbon management index of surface soil was higher in organicallyamended treatments than that of NPK fertilization and Control. T6treatment received ahighest value with231.83.(3) Compared with T1treatment, the organic treatments (T2-T6) improved some nutrientsituation of soil (total nitrogen, available phosphorus, available potassium and CEC) and soilmicrobiological properties [soil microbial biomass C (MBC&N (MBN), urease activity,alkaline phosphatase activity], especially in T5treatment. As follows, MBC, MBN, ureaseactivity and alkaline phosphatase activity increased by42.0%,54.6%,19.7%and7.4%respectively. Meanwhile MBC, MBN and urease activity are positively and significantlycorrelated with available phosphorus and available potassium (P＜0.01), the same to soil totalnitrogen, CEC, and crop yield as well (P＜0.05).(4) A total of twelve important quantitative indices were selected, and factor analysis andminimum Euclidean distance method were employed to evaluate the overall soil fertility. Cropyield was used to verify the evaluation results. Applying organic materials promoted soilfertility and crop yield significantly. Compared with applying chemical fertilizer alone, itscombination with straw compost and with organic manure increased the wheat yield by13.31%and16.17%, respectively. The soil quality under the combined application ofchemical fertilizer with straw compost was the highest, with an integrated score up to58.94,followed by the combined application of chemical fertilizer with organic manure.(5) Forage radish produced quantities of shoots and roots biomass (2763and2326kg ha-1respectively) in the fall, which was obviously higher in amount than that of no-cover crop.The carbon intake for radish shoots and roots were1011and883kg ha-1seperately. The TOCin soil dropped with the deepening of soil, but was not significantly affected by the covertreatment. However, under any nitrogen rates, forage radish’s significant impacts on POXCwere observed in both surface soils and deep soils. Additionally, a strong positive relationshipbetween POXC and SOC has also been displayed in this study (P<0.01). At0-30cm soil layer, compared with the no-cover treatment, POXC in cover treatment soils has increased23%,20%and26%respectively under N56, N112and N168kg ha-1(August).(6) Forage radish takes up N from both the top and deep soil layers, storing the N intissues near the soil surface for use by the next crop. Nitrogen captured in the radish shoots atthe experimental sites was nearly4times greater than in weeds under both N levels. Duringthe later period of fodder carrots growth (December), the NO3-N in the top soil hassignificantly decreased, about18.31%and9.56%under the N fertilization rate of100and0kg N ha-1, respectively. However, after the decomposition of the residues (May), the NO3-Nin the top soil has increased about165.16%and119.56%, and no significant accumulation inthe deep soil. Forage radish had no significant effect on total N and NH4-N in soil.(7) Planting forage radish promoted the growth of following silage corn, and improvedthe production of dry matters of stalks and corn kernels. The nitrogen intake for corn wasobviously increased under N0, N56, N112, and N168kg ha-1,23.88%,6.61%,18.20%and1.75%respectively. When applying no nitrogen, the N intake of corn under cover treatmentwere dramatically higher than those of no-cover treatment, thus lowering the recovery andagronomic efficiency of applied N significantly under the same N fertilization rate.Meanwhile, the recovery and agronomic efficiency of applied N decreased steadily withfertilizer rates increased.Based on the above research, two important conclusions have been drawn in this paper.First, the combined application of organic materials (straw) and chemical fertilizer to soil inarid areas in China, where straw resources are very rich, can regulate the soil bulk density andthe distribution and stability of soil aggregates, and effectively increase the soil aggregateassociated carbon content to significantly improve the soil structure and fertility in the aridareas; meanwhile, a comprehensive evaluation of the factor analysis is employed to accuratelyreflect the soil fertility level and predict the soil productivity. Second, in the soil of U.S.Anortheastern humid areas where the farmland is kept fallow, planting cover crops caneffectively improve the potential of carbon storage capacity, the carbon sink activity potentialand the nitrogen use efficiency to reduce the potential environmental pollution caused byfertilizer. Therefore, the effective way of improving the soil fertility and the fertilizer useefficiency is to plant cover crops and reduce follow-up crop nitrogen fertilizer application inhumid areas.