| The Yellow River Delta area of saline soil is large,the soil structure is poor,the soil is easy to harden and the fertility is low.Soil salinity seriously restricts the land productivity in this area,and it is extremely unfavorable to the growth of wheat and corn,which eventually leads to crop yield reduction.Humic acid is an organic polymer compound,which is rich in various active functional groups and active compounds,and its role in soil improvement,fertilizer efficiency,and crop stress resistance has been paid more attention.To study the effects of humic acid on soil fertility and plant growth in the Yellow River Delta,humic acid fertilizer should be added in winter wheat-summer corn rotation field positioning experiment.In this experiment,potassium humate and organic humic acid applied in four different dosages were used as fertilization modes.Including blank no fertilizer(CK),conventional fertilizer control(CF),potassium humate 75 kg hm-2(HAI-1),potassium humate 150 kg hm-2(HAI-2),potassium humate 225 kg hm-2(HAI-3),potassium humate 300 kg hm-2(HAI-4),organic humic acid 750 kg hm-2(HAII-1),organic humic acid 1500 kg hm-2(HAII-2),organic humic acid 2250 kg hm-2(HAII-3),organic humic acid 3000 kg hm-2(HAII-4),a total of 10 treatments,The effects on the crop of various treatments,biological and photo synthetic properties of plants,stable aggregates of soil water,soil salt content,soil enzyme activity,and basic physical and chemical properties of the soil have been studied.The main research results are as follows:(1)Application of humic acid could improve grain yield,and the highest grain yield under HAI-4 treatment was 9039 kg hm-2.Compared with conventional fertilization,the yield of wheat under potassium humic acid treatment was 14.23%-46.21%,and that under organic humic acid treatment was 4.39%-21.51%.The highest yield of wheat straw under HAI-4 treatment was 10558 kg hm-2,which was 19.9%higher than CF.The highest grain yield of HAI-4 treatment was 10162.13 kg hm-2.Compared with conventional fertilization,the yield of HAI with potassium humic acid fertilizer was 7.12%-19.10%,and that of HAII with organic humic acid fertilizer was 0.04%.The highest yield of corn straw under HAI-4 treatment was 16217.84 kg hm-2,which was 56.4%higher than CF.(2)The application of humic acid had obvious effects on increasing soil organic matter,total nitrogen,ammonium nitrate nitrogen,available phosphorus,available potassium,and reducing soil salt content,and HAI-4 had the best effect.The soil salt content of HAI-4 treatment at different growth stages of wheat season decreased by 27.29%,19.71%and 22.70%compared with CK,respectively,and that of HAI-4 treatment at different growth stages of corn season decreased by 24.27%,15.64%and 37.21%compared with CK,respectively.Both kinds of humic acid fertilizer could promote the formation of soil aggregate structure.In wheat season,the content of>2mm and 2-0.25mm aggregates under HAI-4 treatment was the highest(5.53%and 8.43%),followed by HAI-4 treatment,and CK treatment was the lowest.The soil macroaggregates(>0.25mm)showed an increasing trend with the increase of two kinds of humic acid fertilizer,and potassium humate HAI-4 treatment had the best effect on the macroaggregates(>0.25mm),which was 13.96%.In corn season,the contents of HAI-4 treatment>2mm and 2-0.25mm were the highest,which were 8.45%and 9.61%,respectively.Compared with CK,the two humic acid treatments increased the composition of large aggregates(>0.25 mm),and the best effect of HAI-4 treatment on the composition of large aggregates(>0.25 mm)was 18.06%.Potassium humate increased by 57.2%,59.3%,58.5%and 97.6%compared with CK large aggregate(>0.25 mm)in each treatment,and organic humic acid increased by 21.4-53.3%compared with CK large aggregate(>0.25 mm)in each treatment.(3)Potassium humate HAI-4 treatment effectively promoted the absorption of nitrogen,phosphorus and potassium in wheat and corn plants.Compared with CK plants,HAI-4 treatment in wheat season increased nitrogen,phosphorus and potassium by 96.52%,56.7%and 97.22%,and HAI-4 treatment in corn season increased nitrogen,phosphorus and potassium by 86.50%,59.75%and 52.81%,respectively.The ratio of potassium to sodium in wheat and maize was increased by 242.83%and 63.45%in HAI-4 treatment compared with CK.(4)The results of pot experiment showed that the urease activity of HAI-4 treatment was the lowest,and that of CF treatment was the highest.With the increase of application amount,the inhibition effect on soil urease activity increased.In addition,the two kinds of humic acid application was beneficial to maintain higher photosynthesis of maize.The highest net photosynthetic rate and stomatal conductior of HAI-4 treatment were 6.58μmolCO2 m-2s-1 and 41.92 mmolH2O m-2s-1,respectively.The intracellular CO2 concentration was significantly reduced to 116.56 μmolCO2 mol-1.HAI-4 treatment effectively promoted the growth of maize seedlings.Compared with CK,plant height,stem diameter,leaf area,leaf SPAD value and root growth parameters were significantly increased by HAI-4 treatment,and root activity was increased by 60.40%compared with CK.In a word,in wheat-maize rotation,potassium humate fertilizer of 300 kg hm-2+conventional fertilizer can effectively improve crop yield,enhance photo synthetic characteristics and nutrient absorption ability of plants,promote the formation of soil aggregate structure,enhance salt control ability,and improve soil fertility.The experimental results provide theoretical guidance and technical support for the application of humic acid fertilizer,the improvement of land productivity and the improvement of saline-alkali soil in this area. |
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