Response Of Soil Hydrothermal Condition And Flax Growth To Plastic Film And Nitrogen Fertilizer Types

As one of the most important oil crops in China,oilseed flax is widely used in industry,food industry,health care and cosmetic products in addition to edible oil.Oilseed flax is mainly grown in rainfed and semi-arid agricultural areas,i.e.the Northwest of China,where the soil fertility is poor and rainfall is limited.Thus,the shortage of water and nutrient are main limiting factors of agriculture production in this area.And film mulching combined with rational fertization is one of the effective measures to solve these problems.Field experiment was conducted to study the effects of film mulching and nitrogen fertilizer on the growth of oilseed flax and thermal-moisture characteristics of soil.The treatments included no mulching（P₀）,plastic film mulching（P₁）,degradable film P₂（thickness 0.008mm）,degradable film P₃（thickness 0.010mm）and degradable film P₄（thickness 0.012mm）,fertilization included no fertilization（N₀）,application of inorganic nitrogen alone（N₁）and combined application of organic and inorganic nitrogen（N₂）.The aim of this study was to provide a theoretical basis for high yield cultivation measures of oilseed flax in dry area.The main results are as follows:1.From seedling to budding stages,soil water content of 0⁴0cm soil layer increased by 28.08%⁵2.52%in ordinary plastic films treatment.Soil content in P₂,P₃ and P₄ treatments was 27.24%,27.92%and 21.98%greater than that of P₁treatment respectively at the begaining of anthesis.And there were no significant differences among P₂,P₃ and P₄.Soil temperature was significantly increased by film mulching.From seedling to anthesis stages,there was no significant difference among P₁,P₂,P₃ and P₄.In the later stage,with the degradation of degradable plastic film,the ability of three kinds of degradable film to increase temperature was gradually lower than that of ordinary plastic film.With the increasing of filed closure,the light transmittance decreased and weakend the effects of increasing temperature.2.Plastic film mulching did not affect the content of ammonium nitrogen,but it significantly increased soil nitrate nitrogen content at the initial stage of reproductive growth.Fertilization increased the content of ammonium nitrogen and nitrate nitrogen of soil.In the early growth stage,the effect of application inorganic nitrogen fertilizer alone was greater than that of inorganic and organic nitrogen fertilizer combination treatments,while the opposite trend was appeared in the middle and later stages.Combination organic and inorganic fertilizer increased soil organic matter content.3.Films mulching shortened the growth period of flax.Both of the fertilization and film mulching significantly increased the seedling emergence rate,plant height,stem diameter,leaf area and dry matter accumulation of the flax;the seedling emergence rate reached 75%（P<0.05）under the common plastic film and inorganic nitrogen fertilizer.The promotion effect of common plastic film on elongation and growth of flax plants was higher than that of degraded film.The promotion effect of degraded film on dry matter accumulation was mainly at the seedling stage.The effect of single application of inorganic fertilizer on stem growth was mainly reflected in the vegetative growth stage,while the promotion effect of organic and inorganic application was mainly reflected in the stage of reproductive growth stage.Combined application of organic and inorganic nitrogen fertilizer promoted dry matter accumulation during the whole growth period.4.Film mulching was beneficial to the absorption and accumulation of nitrogen,while the accumulation advantage of ordinary film was mainly in the vigorous growth stage of vegetative growth and reproductive growth,that is,the mid-term of the growth of flax.Plastic film mulching treatments significantly increased the nitrogen use efficiency.Application of nitrogen increased nitrogen accumulation in flax plant,and there was no significant difference between the two fertilization levels at different growth stages.The interaction between plastic mulching and fertilization on nitrogen uptake and accumulation was not significant.5.Mulching significantly increased the number of branches,the number of capsules per plant and 1000-seed weight,and the effect of degradable mulching film on branch number and capsule number per plant was better than that of common plastic film.Fertilization significantly increased the number of branches,the number of capsules per plant and the seed yield.Compared with single application of inorganic fertilizer,combination of organic and inorganic fertilizer siginifantly increased the 1000 grain-weight and the harvest index.The number of capsules per capsulein P₃N₂（22）,and seed grains per capsule of P₀N₂,P₁N₀ and P₁N₁（8.37,8.47,8.40）were the highest under the interaction of plastic mulching and fertilization.6.The increase of grain yield and water use efficiency under film mulching was significant,and the yield of P₄ was up to 789.06kg·hm^-2,but this growth promoting effect was not related to film’s type and its degradation characteristics.The effect of nitrogen application on yield increasing and water use efficiency was significant,in which the grain yield under N₂ treatment was 9.69%（P<0.05）and WUE treated by N₂and N₁ was 13.27%and 10.36%higher than that of N₀ treatment,but there was no significant difference between inorganic fertilizer and inorganic fertilizer.