采用原位室内培养的方法,研究绿肥籽粒苋腐解过程中氮、钾释放规律,并分析不同粉碎程度对籽粒苋腐解过程中氮、钾释放的影响.结果表明,籽粒苋还田腐解前15d,是氮、钾的快速释放期;经过34 d腐解,籽粒苋茎秆氮、钾的养分累积释放率分别达到72.8％和94.2％,其中籽粒苋释放的氮素对土壤无机氮的最大表观贡献率为12.0％,钾素对土壤有效钾的最大表观贡献率为69.8％.不同粉碎程度处理的籽粒苋茎秆还田后,土壤中氮、钾含量变化有差异,土壤铵态氮含量和速效钾含量为T3(添加粒径为5 cm±0.5 cm的籽粒苋茎秆)＞T2(添加粒径为3 cm±0.5 cm的籽粒苋茎秆)＞T1(添加粒径＜2mm的籽粒苋茎秆),土壤无机氮含量为T1＞ T2 ＞T3,土壤缓效钾含量处理间无显著差异.由此表明,籽粒苋腐解释放的氮素对土壤无机氮的表观贡献率远小于钾素对土壤有效钾的表观贡献率,籽粒苋粉碎程度越细越有利于土壤无机氮含量的提升,而粉碎程度越粗越利于土壤速效钾含量的提升.

Two field experiments were conducted to explore the influence of grain amaranth (Amaranthus hypochondriacus) and tobacco intercropping on tobacco growth and potassium uptake during 2014 and 2015.The experiment during 2014 included three treatments,(a) planting tobacco only;(b) tobacco and amaranth intercropping,amaranth was cut and burried into soil after 45 day growth;(c) tobacco and amaranth intercropping,but did not cut and burry.There were 4 treatments during 2015,(d) planting tobacco only;The other 3 treatments were all tobacco and amaranth intercropping,(e) one row of tobacco with 2 rows of amaranth;(f) one row of tobacco with 4 rows of amaranth;(g) one row of tobacco with 6 rows of amaranth.We analyzed tobacco dry matter accumulation,tobacco potassium concentration,potassium uptake,soil available potassium and soil slow-release potassium in the three intercropping systems.The results showed that,compared with treatment (a),amaranth intercropping without returning to the field (treatment c) increased dry matter accumulation in tobacco roots.Potassium concentration showed no significant changes,while potassium content increased by 70％.Dry matter accumulation reduced by 11％ and 14％ respectively in stem and leaves,while potassium contents were 0.11％ and 0.12％ lower and potassium concentration 16％ and 12％ lower.For the treatments with amaranth returning to the field,the highest potassium concentration in leaves was recorded.The different intercropping systems showed different amounts of dry matter accumulation,potassium content and potassium concentration.Dry matter accumulation and potassium contents in root,stem,upper leaves and middle leaves increased in the 2 rows (e) and 4 rows (f) treatments and decreased in the 6 rows (g) treatment.Dry matter accumulation in the upper and middle leaves was lower in treatment (e) than (f),but the former's potassium concentration and potassium content were higher.The concentration of soil available potassium in the tobacco rows increased in the intercropping systems,but the concentration of soil slow-release potassium did not change.The intercropping systems without grain amaranth returning showed lower soil available potassium concentrations than those with amaranth returning.Among the treatments in the amaranth returning system,the growth in soil available potassium was largest in treatment (g),which increased by 91％ and 35 ％ when returned after 20 and 60 d respectively.Soil available potassium increased by 54％ and 23％ in (f) over these periods.The analysis of apparent potassium flow showed different results for the various amaranth returning systems.About 42％-52％ of potassium was uptaken by the tobacco in treatments (e) and (f),while only some 17％ was absorbed in treatment (g).This study suggests that the most favorable planting pattern is the amaranth-tobacco intercropping system with 2 rows of amaranths and returning amaranth to the field after 45-55 d growth.

In order to study the returning effect of Amaranthus hypochondriacus on soil fertility,an incubation experiment was carried out to simulate the returning of A.hypochondriacus as green manure to the field.The dynamic change in concentrations of DOC (soil dissolved organic carbon),Nmin (mineral nitrogen),available potassium and slowly released potassium was measured in the soil with plants harvested on 45,55 and 65 d af-ter growth.During the first 14 d of incubation,the concentrations of soil DOC,Nmin,available potassium and slowly released potassium increased significantly compared to the control.Apparent nitrogen release rate in A.hypochondriacus was more than 19.5%,and for potassium,it was above 63.4%.During 14-56 d of incu-bation,soil Nmin,available potassium,slowly released potassium concentrations showed the order as sample harvested on 45 d after growth>55 d>65 d>Control,but there were no differences in soil NH4 +-N and DOC concentration between the treatments and control (for NH4 +-N,sample harvested on 45 d as an exception). After 56 d of incubation,Nmin concentration in the soil was 3.4 times of that under Control,available potassi-um concentration was at least 3.1 times and slowly released potassium concentration was at least 1.1 times un-der all treatments with A.hypochondriacus .In addition,the treatments using A.hypochondriacus harvested on 45 d resulted in lower apparent release rates of nitrogen and potassium than the other two treatments using A.hypochondriacus during the incubation.Conclusively,returning A.hypochondriacus to soils obviously im-proved soil available nutrients,and the plants harvested on 45 d showed better effect on soil fertility.