| Saline-alkali land is one part of important land resources in China.Among of them,the area of coastal beaches in Jiangsu Province more than 0.658 million ha,is the largest coastal area than other provinces,and it is the most important reserve land resource in Jiangsu Province.Forage sorghum is an important forage crop,which has strong tolerance to saline and alkali soil.It is the best choice to planting it in saline-alkali land.With the development of animal husbandry and adjustment of agricultural planting structure,the planting area of forage crops is decreasing and the high-yield cultivation techniques for forage crop in saline soil is lacking.Therefore,field experiment was conducted at Dafeng Coastal Forest Farm(33°20’N,120°47’E)in Yancheng,Jiangsu Province in 2018.Canadian forage sorghum CFSH-30 was used in this study.The planting density(300,000,500,000 and 700,000 plants/ha)and three nitrogen application rates(0,150,300 kg N/ha)were arranged to study the growth,yield,physiological characteristics and quality of forage sorghum.The main results as follows:1.Effects of Planting Density and Nitrogen Rate on the Growth Traits and Biomass Production of Forage Sorghum Grown in Saline SoilsWith the growth and development of sorghum,the sorghum plant height,fresh weight and dry weight continued to increase;the stem elongation generally showed gradually decreased,and it is the lowest at heading-maturity period;and the relative growth rate generally increased firstly and then decreased,the maximum value showed at the flag leaf stage-booting stage.The stem elongation,fresh weight and dry weight of forage sorghum were increased with planting density increased,and they all reached the maximum under high planting density.Plant height,stem elongation,fresh weight,dry weight,and relative growth rate of forage sorghum were increased with the increasing of nitrogen application rate,and reached the maximum under high nitrogen(N3)conditions.At jointing stage,flag leaf stage,and booting stage,the combination of high density with high nitrogen rate(D3N3)generated the highest fresh and dry biomass yields,which the fresh biomass yields was 81255 kg/ha,96232 kg/ha and 125024 kg/ha,and dry biomass yields was 20313.8 kg/ha and 27494.9 kg/ha,respectively.And under the medium density and high nitrogen(D2N3)combination treatments,the highest fresh biomass and dry biomass yields were produced at heading stage and maturity stage,which the fresh weight biomass yields were reached 144113 kg/ha and 169763 kg/ha,and dry biomass yields were,reached 51468.9 kg/ha and 67905.2 kg/ha,respectively.2.Effects of Planting Density and Nitrogen Rate on Physiological Characteristics of Forage Sorghum Grown in Saline Soils along the BeachNeither MDA content was decreased nor content of sucrose and starch were accumulated not so much under high planting density.While reducing planting density can appropriately reduce MDA content and increase sucrose and starch content.Low planting density was beneficial to the accumulation ofN,P and K contents in the jointing stage,flag leaf stage and booting stage.Medium planting density was beneficial advantage to the accumulation chlorophyll a,chlorophyll b,and chlorophyll(a+b),N,P and K contents at heading and physiological maturity stages.Planting density had no significant effects on the content of proline,soluble sugar and the activity of SOD,CAT,and POD.Medium nitrogen rate was beneficial to the accumulation of proline and soluble sugar.High nitrogen rate significantly reduced MDA content and increased the activity of SOD,CAT,and POD,and the content of chlorophyll a,b,and chlorophyll(a+b),sucrose,starch,N,P,and K.In terms of the interactive effects of planting density and nitrogen rate,at the density of 300000 plants/ha,the application of nitrogen at 300 kg N/ha significantly reduced MDA content and increased the content of N,P,K.At the planting density of 500,000 plants/ha,soluble sugar content was higher at 150 kg N/ha and the activity of SOD,CAT,and POD,and the content of chlorophyll a,b,and(a+b),sucrose,and starch was higher at 300 kg N/ha3.Effects of Planting Density and Nitrogen Rate on Quality Characteristics of Forage Sorghum Grown in Saline SoilsPlanting density and nitrogen fertilizer application were significantly on affect quality of forage sorghum forage quality were significant.The content of crude protein and crude fat generally increased firstly and then decreased with the increase of planting density,and the content of crude fiber was the highest at low density(300,000 plants/ha),).However,the content of crude fiber was the opposite.Within a certain range of nitrogen application,the contents of crude protein and crude fat contents of forage sorghum in heading stage increased with the increase of nitrogen application,and the crude protein and crude fat contents were the highest at the level of high nitrogen application(300kg N/ha)at heading stage.On the contrary,the content of crude fiber content was the lowest at the level of high nitrogen application(300 kg N/ha).However,under the combined action of planting density and nitrogen fertilizer,the contents of crude protein and crude fat under the medium density and high nitrogen(D2N3)treatment was were the highest under the medium density and high nitrogen(D2N3)treatment,which reaching reached 89.87 g/kg and 1.99%,respectively.The lowest content of crude fat content was 21.21%under low density and high nitrogen treatment。This study suggested that the suitable planting density and nitrogen application rate in moderate saline-alkali soils are 500,000 plants/ha with 300 kg N/ha.As used for silage forage,the best harvest time is at the heading stage,which can maintain the higher yield and better quality during this time. |
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