| In Hetao Irrigation District,many researches put the spotlight on the effects of irrigation rate and N application rate on soil and yield,but there are few studies on the effects of irrigation and N application rate as well as their interactions on soil properties and sunflower yield.In this study,the empirical framework of maintaining soil quality under the salt-leaching mode in Hetao Irrigation District was summarized by using the methods of literature review and field research.A two-factor(irrigation rate and N application rate)split-plot design was used to evaluate the effects of irrigation rate and N application rate on soil properties and sunflower yield.Three replications were made for this experiment.The main treatment:irrigation rate,including three levels—I1,I2,I3(5110,4050,2985 m~3/hm~2,of which 4050 m~3/hm~2was conventional irrigation rate for local farmers).The secondary treatment:N application rate,including four levels—N0,N1,N2,N3(0,750,600,450 kg/hm~2,of which 600 kg/hm~2was the conventional amount of fertilizer applied by local farmers).Sunflower(SH363)was used as the crop for experiment.The results of this study can provide a theoretical basis for reasonable management of irrigation requirement and fertilizer application in sunflower production,improving soil quality and maintaining soil sustainable development.The results of this study are as follows:(i)This study put forward the empirical framework of maintaining soil quality under the salt-leaching mode in Hetao Irrigation District,including seven elements:flood irrigation,land leveling,plastic film mulching,fertilization,soil organic matter(SOM),p H value and salinity.Hetao Irrigation District is characterized by flood irrigation with high irrigation rate,high amount of fertilizer application,low soil organic matter(SOM),high p H value,great variation of salinity,etc.The average SOM and p H value have been kept in the range of 10.9-13.9 g/kg and 8.0-8.15 in recent 35 years,respectively,showing a slight upward trend.(ii)T test results showed that the SOM(12.91 g/kg)before soil preparation under low irrigation rate(I3)in spring was significantly lower than that after soil preparation and spring irrigation(14.18 g/kg)(0-20 cm soil layer);in 0-20 cm soil layer,the cation exchange capacity(11.98 cmol/kg)before soil preparation under I3 was significantly higher than that after soil preparation and spring irrigation(10.99 cmol/kg);the content of soil available phosphorus and available potassium before soil preparation and spring irrigation was significantly lower than that after soil preparation and spring irrigation;the content of nitrate nitrogen,total nitrogen and total salt in soil before soil preparation and spring irrigation was significantly higher than that after soil preparation and spring irrigation.(iii)The results of ANOVA showed that the content of TN in soil under high irrigation rate(I1)(2.00 mg/kg)was significantly lower than that under I3(2.77 mg/kg);the content of TS in soil under I1(1.57 g/kg)and medium irrigation rate(I2)(1.73 g/kg)was significantly lower than that under I3(2.25 g/kg).In 0-20 cm soil layer,the content of TN in soil under high N application rate rate(N1)(0.73 g/kg)and medium N application rate(N2)(0.67 g/kg)was significantly higher than that under the control(N0)(0.54 g/kg),and the content of TN in soil under N1(2.73 mg/kg)was significantly higher than that under N0(2.04 mg/kg);in20-40 cm soil layer,the content of TN in soil under N1(0.52 g/kg)was significantly higher than that under N0(0.40 mg/kg),the content of TN in soil under N1(2.73 mg/kg)was significantly higher than that under N0(2.04 mg/kg),and the content of N in soil under N1(2.70 mg/kg)was significantly higher than that under N0(1.61 mg/kg),N2(2.36 mg/kg)and low N application rate(N3)(2.20 mg/kg).In 0-20 cm soil layer,the cross term of irrigation rate and N application rate significantly affected SOM.In the condition of N1,the SOM under I1(12.36g/kg)and I2(13.00 g/kg)was significantly higher than that under I3(10.66 g/kg).In the condition of I3,the SOM under N3 was significantly higher than that under N1.(iv)The content of kernel under N1(51.11%)was significantly higher than that under N0(48.34%);the diameter of sunflower disk under N2(22.71 cm)and N3(22.87 cm)was significantly higher than that under N0(21.01 cm);in the condition of I2,the diameter of sunflower disk under N2(23.69 cm)was significantly higher than that under I2 and N1(20.21cm);in the condition of I3,the diameter of sunflower disk under N3(24.74 cm)was significantly higher than that under N1(21.45 cm)and N0(21.54 cm).The P value of the cross term of irrigation rate and N application rate was less than 0.05.In the condition of N2,the yield under I1(3721.65kg/hm~2)and I2(4421.70 kg/hm~2)was significantly higher than that under I3(3205.80 kg/hm~2);in the condition of N3,the yield under I2(2984.70 kg/hm~2)was significantly lower than that under I1(4034.85 kg/hm~2)and I3(4366.50 kg/hm~2).In the condition of I2,the yield under N2(4421.70 kg/hm~2)was significantly higher than that under N0(3316.20 kg/hm~2)and N3(2984.70 kg/hm~2);in the condition of I3,the yield under N3(4366.50 kg/hm~2)was significantly higher than that under N0(3537.30 kg/hm~2),N1(3316.20 kg/hm~2)and N2(3475.80 kg/hm~2).According to the above results,the conclusions are drawn as follows:(i)The empirical framework proposed in this study can be used as a theoretical norm for evaluating soil quality under salt-leaching by irrigation.Under the condition of salt-leaching by irrigation,the soil quality in Hetao Irrigation District showed a stable trend with time;using this framework,we can find soil problems and adjust some unbalanced factors to maintain the stability of soil quality,and can also provide a reference for other areas.(ii)After spring irrigation and soil preparation,the TN,cation exchange capacity,SOM,TS,TN,available phosphorus and available potassium content,and alkalinity were significantly improved.(iii)The irrigation rate significantly decreased the TS in soil.The N application rate significantly increased the content of TN and TN in soil.The cross term of irrigation rate and N application rate had significant effects on the SOM.(iv)The irrigation rate had no significant effect on sunflower yield,the N application rate had a significant effect on the diameter of sunflower disk,and the cross term of irrigation rate and N application rate had significant effects on sunflower yield and disk diameter.(v)Taken together,I3 was the best irrigation rate and N3 was the best N application rate. |
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