| High crop yield and soil fertility are all important parts of sustainable agricultural development, while maintaining or improving soil fertility assures higher yield and better quality of crop. Soil fertility is the basic property of soil, and also reflects soil physical, chemical and biological properties. The sudangrass(Sorghum sudanense) and ryegrass(Lolium multiflorum L.) rotation was a new type and more intensive cropping system in the south of China, which developed very fast in recent years, and growth areas increased gradually. In this roration, harvest frequency and intensity for two forage are high. As a more intensive cropping system, it was important to take proper nutrients measures to increase crop yield, maintain soil fertility, nutrients balance, including the change of soil productivity, sudangrass(Sorghum sudanense cv. Yanchi) in summer and ryegrass(Lolium multiflorum cv. Abundant) in winter was conducted based on located field experiment and pot experiment. The experimental design was consisted of 5 treatments in a randomized block design with four replicates, including control (CK), fertilizer phosphorus and potassium (PK), fertilizer nitrogen and potassium (NK), fertilizer nitrogen and phosphorus (NP) and fertilizer nitrogen, phosphorus and potassium combination (NPK), including three levels of N (N0, N1, N2), P (P0, P1, P2), K (K0, K1, K2). The objectives of this study were that effects of NPK fertilizers on forage growth, yield and quality, soil fertility. The major results as follows:1) Forage growth and physiological indexThe Combination of NPK fertilizer could increase forage growth and improve physiological index. The height, leaves, leaf length and width of forage in NPK treatment were higher than that in other treatments both field and pot experiment. Fertilizer N obtained the highest response, following by fertilizer P and K.In the field experiment in Wuhan, chlorophyll, net photosynthetic rates, POD of ryegrass in NPK treatment were higher than that of CK and PK treatments, and transpiration rate, MDA of ryegrass in NPK treatment were lower than that in CK and PK treatments, while OM, NP and NK treatments were similar to NPK treatments.2) Yield and qualityNPK combination also increased yield and quality of forage. In the field experiment in Honghu, total yield of NPK treatment were 110.7 t/hm2-162.7 t/hm2, and average yield were 131.9 t/hm2, and were 234.6%,26.2%,21.1% higher than that of PK, NK and NP treatments. In the field experiment in Wuhan, total yield of NPK treatment were 100.7 t/hm2-122.4 t/hm2, and average yield were 110.6 t/hm2, and were 429.3%、47.30%、24.4% higher than that of PK, NK and NP treatments. In the pot experiment, total yield in NPK treatment were 1387.2 g/pot-2091.3 g/pot with the average yield of 1673.4 g/pot, and were 234.6%,26.2%,21.1% higher than that in PK, NK and NP treatments, respectively. In the rotation, the increasing effect of fertilizer N was the higher than that of fertilizer P and K, and the increasing effect of fertilizer N was the lowest.In the field experiment in Honghu, crude protein in NP, NK and NPK treatments was higher than that in CK and PK treatments, but nitrogen free extract was lower. Crude fiber and ether extract in all treatments with fertilizers in soil was higher than that in CK treatment, while there was not different for crude ash between treatments.3) Nutrients uptake and balanceNPK combination also promoted nutrients uptake of forage grasses, and improved nutrients balance in the rotation. Total N uptake for NPK treatment in the field and pot experiment was 2128 kg/hm2,31.95 g/pot for five years, and total P uptake was 184 kg/hm2, 3.85 g/pot, and total K uptake was 2796 kg/hm2,34.04 g/pot, and were higher than that of other treatments. In the rotation, fertilizer N played the highest role in improving N, P and K uptake, compared to fertilizer P and K.Fertilizer N and P could maintain N and P balance in the rotation in the field and pot experiment, but K balance was deficient. NPK combination also decreased N and P surplus in soil, maintain nutrients balance, and degraded the K depletion in soil.4) Weed investigationMore weeds occurred in the sudangrass season in the rotation. Chinese Sprangletop (Leptochloa chinensis (L.) Nees), American Sloughgrass (Beckmannia szigachne (Steud.) Fern.) were preponderance weeds. NPK increased weed growth and yield, total yield in NPK treatment were 273.6%,32.8%,5.4% higher than PK, NK and NP treatments, respectively. There were nutrient competitions between forage and weed after fertilization in the rotation.5) Fertilizer and water use efficiencyNPK combination improved fertilizer use efficiency and water productivity. Average N, P and K fertilizer use efficiency were 48.1%,20.9% and 47.4% for five years in the field experiment, and were 60.9%,35.7% and 70.5% for five years in the pot experiment, respectively.Water productivity of forage in NPK treatment was 15.6 kg/m3-18.8 kg/m3 with the average of 16.4 kg/m3, and were 457.2%,259.7%,17.8% higher than that of PK, NK and NP treatments.6) Soil fertilityThe result in both field and pot experiment indicated, with increasing time in the ration, soil organic matter, total N and P, extractable P in NPK treatment increased, but pH, total K, slow release K, available K changed less. NPK combination could increase active organic matter, and improve soil fertility. Fertilizer N could increase the content of total N, and NH4+-N. Fertilizer P also increased the content of Al-P, Fe-P, O-P in soil, but influenced less the content of Ca-P. Fertilizer K also increased the content of slow release K, available K, but affected less total K.Fertilizer N degraded AWCD, Simpson index, McIntosh index, but there were no differences between Shannon indexes in all treatments. Throughout principal component analysis (PCA), there were differences between C sources utilization by microbial communities. MBC, MBN, activities of sucrase and urease in soil following the application of fertilizer N were higher than that of other treatments. In the field experiment, alkaline phosphatase activities in soil following the application of fertilizer N were lower than that in other treatments, while alkaline phosphatase activities in the pot experiment were converse.In the field experiment, NPK combination decreased bulk density and increased porosity in soil. |
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