| For a long time,the wheat-maize has been the main crop rotation in Huang huai Plain.Aimed at problems that the unreasonable crop layout and nitrogen fertilizer reduction in this areas,two field experiments were set up.Experiment 1:three treatments with wheat and legume crop rotation were set as:(1)wheat-maize rotation,(2)wheat-summer peanut rotation,and(3)wheat-soybean rotation.Experiment 2:four treatments with different wheat sowing rates and different levels of nitrogen applied:(1)conventional wheat sowing amount+conventional fertilization(CBCF);(2)30%increase of the conventional sowing rate+conventional nitrogen application(ZBCF);(3)30%increase of conventional sowing amount+20%reduction in conventional nitrogen fertilization(ZBJF);(4)conventional sowing amount+20%reduction in conventional nitrogen fertilization(CBJF).The soil physical,chemical and biological properties in different soil layers and crop yield were measured and analyzed.The results provided theoretical basis for optimum crop rotation patterns,wheat sowing and nitrogen combination selection.The main findings were as follows:Experiment 1 Crop rotation patterns:(1)After a CBCF treatment in 2018.The economic benefit was increased under ZBJF and CBJF in 2017 and rotation cycle,compared with wheat-corn treatment,wheat-peanut and wheat-soybean treatments reduced soil bulk density and increased porosity.The soil bulk density under wheat-peanut and wheat-soybean treatments in 0-10 cm in summer season 2018 decreased 0.06 and 0.04 g/cm3,respectively,compared with that in 2017.While the soil specific gravity under all treatments was changed little,and the soil porosity under wheat-peanut and wheat-soybean treatments was slightly increased.(2)After a rotation cycle,Compared with the summer in 2017,the soil organic matter(SOM)content under wheat-soybean treatment in 0-30 cm was increased;and the total nitrogen(TN)content under wheat-peanut and wheat-soybean treatments in 10-20 cm was increased.The soil alkaline nitrogen(AN),ammonium nitrogen(NH4+-N)and nitrate nitrogen(NO3--N)contents under wheat-peanut and wheat-soybean treatments in 0-30 cm were increased,while the soil available phosphorus(AP)and available potassium(AK)contents was decreased.The AN content under wheat-soybean treatment in 0-10 cm was up to 131.28 mg/kg;and the NO3--N and NH4+-N content under wheat-soybean treatment was significantly increased compared with the other treatments.After a rotation cycle,the soil dissolved organic carbon(DOC)and dissolved organic nitrogen(DON)content under all treatments in 0-20 cm was all increased,which was the highest one under wheat-soybean treatment.(3)After a rotation cycle,the soil urease activity under wheat-soybean treatment in 0—30 cm was declined in the summer season 2018 compared to 2017.However,the soil sucrase and neutral phosphatase activities under wheat-soybean and wheat-peanut treatments in 0—30 cm were increased.The soil microbial biomass carbon(SMBC)and microbial biomass nitrogen(SMBN)under wheat-summer peanut and wheat-soybean treatments were increased.The wheat yield and fertilizer partial productivity increased significantly in 2018 compared with that in 2017,and the wheat yield and nitrogen fertilizer partial productivity under wheat-peanut and wheat-soybean treatments were significantly higher than that under wheat-corn treatment in the summer 2018 compared to 2017.The wheat yield under wheat-peanut and wheat-soybean treatments was increased,and farmers' income was increased.Experiment 2:Density-increasing and nitrogen-saving of wheat:(1)Compared with 2017,the bulk density under ZBCF treatment in 0-10 cm and the bulk density under CBJF treatment in 10-20 cm was decreased.The soil porosity under CBJF treatmentin 0-10 cm was increased.(2)The SOM,TN,AN,AP,AK,NO3--N and NH4+-N content in the 0-30 cm soil layer decreased gradually with soil depth in 2017 and 2018.In 2018,the SOM content under ZBJF and CBJF treatments was higher than that under CBCF and ZBCF treatments in 10-30 cm,and the SOM content under ZBJF treatment increased by 18%compared with that in 2017.In 2017,there was little difference of the TN content among the treatments,whereas,it was significantly higher under CBCF treatment in the 0-20 cm in 2018.The difference of AN content under all treatments focused on 0-10 cm,and which was highest under ZBCF treatment in 2017,and under CBCF treatment as 118.86 mg/kg in 2018.The NO3--N and NH4+-N content under the treatments with conventional nitrogen rate(CBCF and ZBCF)were significantly higher than that under treatments with nitrogen reduction(ZBJF and CBJF)in 0-30 cm in 2017 and 2018.The AP content under ZBCF and CBJF treatments in 0-10 cm was increased,and which was increased by 13.14%and 28.54%,respectively in 2018 compared with that in 2017.In 2017,the AK content under CBJF treatment in 0-10 cm in 2018 was increased by 35.71%compared with that in 2017.(3)The SMBC,SMBN and the three enzyme activities decreased with the soil depth in the two seasons.The urease activity and sucrase activity under ZBJF treatment in 0-20 cm were significantly higher than other treatments in wheat season and maize season 2017,and the highest of urease activity was 3.16[NH3-N mgl(g·24h)],the soil neutral phosphatase activity was highest in the 0-20 cm in the three seasons,and the highest was 9.01[Phenol mg/(g-24h)].The nitrogen partial productivity under nitrogen reduction treatments(ZBJF and CBJF)was significantly increased comparing with CBCF treatment,which was increased 28.35%and 46.03%,respectively,in 2018.The wheat yield was not differed from treatments in 2017;while,which was increased by 13.79%and 30.62%under ZBJF and CBJF treatments,respectively,compared with CBCF treatment in 2018.The economic benefit was increased under ZBJF and CBJF in 2017 and 2018.And the economic benefit was increased by 33.70%and 67.11%under ZBJF and CBJF treatments compared with that under CBCF treatment in 2018.In summary,wheat-peanut and wheat-soybean rotation are beneficial to fertilize the soil and increase crop yield and farmers' income.In terms of sowing amount and nitrogen fertilizer interaction,the soil chemical and biological properties were improved under conventional sowing+nitrogen reduction of 20%treatment,it was recommended to reduce the amount of nitrogen fertilizer when sowing. |
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