| Water and nutrient are two important factors restricting the improvement of the crop yield in dryland farming,and the rational close planting is the basis of high yield cultivation.The rainwater-harvesting planting model is high efficient water use cultivation technology,it can effectively improve the rainfall utilization efficiency and improve the water status of dryland crops,and is applied to the dryland farming in northwest of China.In order to improve and expand the application of rainwater-harvesting planting technology in arid regions,and to further excavate its water production potential in the dry farmland,the research of optimization fertilizer application rate and planting density was carried out to search the suitable planting scheme under rainwater-harvesting planting,where the foxtail millet,a kind of traditional cultivation crop in semi arid area,was taken as the object in the present reseach.The field experiment included two planting modes of rainwater-harvesting planting(R)and traditional plat planting(T),four fertilizer application rate(F0,F1,F2,F3),three different planting density(D1,D2,D3),was carried out to study the impact of fertilization and planting density on plant growth,soil moisture and nutrient status,yield formation,water and fertilizer use efficiency under different planting patterns.The main reseach result was as follows:1.The effect of planting pattern,fertilization and planting density on soil water condition in the farmland(1)Compared to tradition flat planting,as the ridge film-mulching and accumulating the rainwater effectively,the rainwater-harvesting planting could reduce the invalid soil water loss.Thus,the soil moisture at 0-200 cm soil layer were all improved at different growth stages both in the rainy year and the normal year.In the normal year,soil water content at 0-60 cm soil layer was increased by 6.8-7.0% and 6.5-30.7% under rainwater-harvesting planting compared with traditional flat planting,respectively at the seedling and booting stage of foxtail millet.The soil water in deeper soil layers was consumed with the development of the growth of foxtail millet,and rainwater-harvesting planting improved the deep soil moisture at filling and harvest stages.In comparison with T,the filed evapotranspiration under rainwater-harvesting planting was reduced by 5.4%(mm),11.1%(41.4 mm)and 8.5%(35.1 mm)in 2013-2015,respectively.(2)Increase of fertilizer and planting density both could increase the consumption of soil water and lower the soil moisture in the deep soil layer.The annual performance was affected by rainfall characteristics and farmland basic fertility.In 2013,due to the more rainfall in the jointing period,the effect of fertilization and density on soil moisture was showed mainly in the filling and harvest stages of foxtail millet.With the increase of fertilizer applicate rate and planting density,the crop water consumption increased significantly,resulting in the reduction of soil water content;In 2014,the difference of soil moisture among different fertilizer application rates was mainly showed in the filling and harvest stages,and the soil water content decreased significantly with the increase of planting density under same fertilizer level.In 2015,the effect of planting density on crop water consumption was mainly found during vegetative growth period,but fertilization had effects throughout the whole growth stage of foxtail millet.The soil moisture at booting and filling decreased with the increase of the planting density and fertilization in 2015,but at harvesting,there was no obvious difference among differernt planting density under traditional flat planting,for rainwater-harvesting planting,there was no obvious difference on soil moisture between D2 and D3,which were both lower than D1.2.The effect of planting pattern,fertilization amount and density on the growth of foxtail millet.(1)Fertilization could promote the growth of millet,and significantly increased the plant height,stem diameter,leaf area and leaf area index(LAI)of the foxtail millet,and further improve the dry matter accumulation of individual and population according to three experimental years.After fertilizer application rate exceeded F2(N 186 kg·ha-1 + P2O5 96 kg·ha-1),there was little futher improvement on foxtail millet growth.The planting density generally had a negative effect on individual growth of foxtail millet.However,the population growth parameters,such as LAI and population dry matter accumulation,trended to increase with the increase of the density.In 2015,due to poor water and soil fertility conditions,the planting density had no obvious effect on population dry matter accumulation.Compared to traditional flat planting under the same planting density,rainwater-harvesting planting could also promote the individual growth,such as plant height,stem diameter and leaf area.However,because of the lower population number in per unit area,the LAI,dry matter accumulation and other population parameters were significantly lower than traditional flat planting.(2)In the normal year,both the translocation amount and transfer rate of the vegetative organs dry matter increased with the increase of the fertilizer application rate,and reached the maximum under F1 or F2 fertilizer level.Too much fertilization was not conducive to the translocation of dry matter from the nutritional organs to the grain.High planting density could increase the total traslocation amount of dry matter,but the transfer rate and conversion rate had different trend under different fertilizer application rate.Compared to traditional flat planting,rainwater-harvesting planting could significantly increased the dry matter transfer rate of each nutrient organ and promoted the translocation of dry matter from vegetative organs to grain,and improved the conversion rates by 14.7% and 61% in 2014 and 2015,respectively.3.The effect of planting pattern,fertilization and density on the yield,yield formation and water use efficiency.(1)The fertilization could significantly increase the grain yield and water use efficiency(WUE)of foxtail millet.As the fertilization amount exceeded F2(N 186 kg·ha-1 + P2O5 96 kg·ha-1),harvest index(HI)decreased,besides that,the fertilizer agronomic efficiency and partial productivity decreased significantly,and the futher increase of foxtail millet yield and WUE were not significant in the normal year under both two planting patterns,but there was a significant futher increase traditional flat planting in the rainy year.Fertilization could significantly improve the thousand seeds weight than no fertilizer,however,the further increase the foxtail millet yield by fertilization was mainly via increasing the number of grains per ear.(2)under nutrient-rich condition,the increase of planting density could significantly improve the foxtail millet yield,WUE,and the fertilizer use efficiency in the rainy year;In the normal year,high planting density would lead to the excessive consumption of vegetative growth on soil moisture,which was not conducive to the final formation of the grain yield,whcih resulting in a significant decrease in HI and WUE.Under the same planting density,the number of the seedling in per unit area under rainwater-harvesting planting was 25% lower than traditional flat planting,thus,when fertilizer application rate was sufficient,it shoud be necessary for rainwater-harvesting planting to increase planting density moderately to improve high yield and WUE;In the rainy year,it was recommended that the highest density(D3: the row spacing of 30 cm,plant distance of 5.5 cm)should be adopted;In the normal year,the planting density should be reduced to middle planting density(D2: row spacing of 30 cm,plant distance of 7.5 cm);For the flat planting,when the planting density was higher than D2,the further increase of yield and WUE was not remarkable,even resulting in the decrease in the farmland with poor soil fertility(2015).(3)In the rainy year,rainwater-harvesting planting trended to decrease of yield and WUE compared with traditional flat planting,and the reduction of yield and WUE increased as increase of fertilizer application rate and planting density,there were remarkable reduction of yield and WUE,decreased by 14.3% and 11.4% respectively compared with traditional flat planting.In the normal year and the suitable planting density,there was significant higher yield under rainwater-harvesting planting,under moderate fertilizer application rate and planting density with 333300 seedlings per hectare,the yield increased by 8% and 6.1% compared with traditional flat planting in 2014 and 2015,respectively.4.The effect of different fertilizers on the nutrient uptake,translocation and nutrient utilization efficiency under different planting pattern.(1)Fertilization can increase the nitrogen and phosphorus accumulation in different organs of foxtail millet.However,the contribution rate of nitrogen and phosphorus on grain increased first and decreased later,and achieved the maximum under F1 or F2 fertilizer level;As increase of fertilizer application rate,the transfer rate of the pre-anthesis nitrogen and phosphorus,the absorption efficiency of nitrogen and phosphorus(NupE/PupE),harvest index(NHI/PHI)and use efficiency(NUE/PUE)all decreased.(2)Under 333300 seedlings per hectare,in the normal year,compared to traditional flat planting,rainwater-harvesting planting could improve the transfer rate of the pre-anthesis nitrogen and nitrogen and phosphorus accumulation at the flowering stage of foxtail millet plant organs;At harvest,rainwater-harvesting planting lowered the nitrogen and phosphorus accumulation amount in nutritional organs,and significantly improved the nitrogen and phosphorus accumulation amount in grain,as well as improved the contribution rate of nitrogen and phosphorus from nutritional organs to grain.However,there was no significant increase of the total nitrogen and phosphorus accumulation under rainwater-harvesting planting;In comparison with traditional flat planting,rainwater-harvesting planting improved the uptake efficiency,harvest index and utilization efficiency of nitrogen and phosphorus.There was no significant difference in the accumulation and utilization efficiency of nitrogen and phosphorus among two planting patterns in the rainy year.5.The effect of different fertilizer application rate on the available nutrient residues under different planting pattern.(1)The fertilization could increase the amount of nitrate nitrogen in the soil at heading stage,to provide adequate nutrient environment for growth.The nitrate nitrogen leaching depth increased with increasing rainfall in the growth period with the maximum accumulation peak in the soillayer below 60 cm of the nitrate nitrogen leaching in harvest period as well as in 120 cm soillayer in the rainy year.When the fertilization amount exceeded F2(N 186 kg·ha-1 + P2O5 96 kg·ha-1),the residual concentration of nitrate nitrogen increased;In the rainwater harvesting planting compared with the flat planting,under the high fertilization and R,the residual concentration of soil nitrate nitrogen increased obviously and the leaching depth increased by about 20 cm.The excessive fertilization would relatively increase in-depth leaching risk of soil nitrate nitrogen under rainwater-harvesting planting.(2)At harvest,the available phosphorus in soil was mainly concentrated in 0-20 cm soil layer,and the concentration was increase with the increase of fertilizer application rate.Under F2 fertilizer level,the content of effective phosphorus could reach more than 5 mg kg-1,which could maintain the balance of phosphorus in soil.In comprehensive analysis,yield and WUE of foxtail millet under rain-harvest planting model could be effectively enhanced by optimizing fertilizer application and planting density,and it could be concluded that the reasonable fertilizer application level was F2(N 186 kg·ha-1 + P2O5 96 kg·ha-1)in semi-arid areas with annual rainfall below 400 mm,in order to increase yield potential,water and fertilizer use efficiency of foxtail millet under rain-harvest planting model,a higher density in the planting furrow would be appreciated,the reasonable planting density for cv.Datong29 was 333300 seedlings per hectare,row space 30 cm,space between seedlings 7.5 cm. |
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