Study On Nutrient Status Investigation And Evaluation For Paddy Soils From Different Main Rice Planting Regions In Hubei

In Hubei province paddy soil is most widespread and rice is most important crop. Itis very significant to ravel the nutrient status of soils in main rice planting regions in orderto manage the nutrients, improve both yield and benefit. Choice suitable soil test methodis precondition for carrying out soil testing and fertilizer recommendation technology in alarge-scale and long-term. In this research the soil nutrients content of the samples, whichwere collected from four main rice planting regions for different cropping system patternsin southeastern, middle, north and Jianghan Plain in Hubei, were analyzed used standardor general test method (GT), a systematic approach (ASI) and Mehlich 3 method (M3).These three test methods were also evaluated using sorghum and rice pot experiments andrice field trial. The purpose of the study is: 1) to find out soil nutrients status and mainlimiting factors in main rice planting regions; 2) to offer science basis for selectingfast-going and large-scale soil test method. The main results were summarized as follows.(1) The macro-secondary-micro soil nutrients status were studied and the resultsraveled the main limiting factors in the four main rice planting regions. The soil pH wasat neutral or slight acid level. Soil organic matter (by GT method) was in moderate and atsuitable level, but alkali soluble organic matter (by ASI method) was low in southeasternregion. Total nitrogen was at middling level for most soil, but alkali-hydrolyzed nitrogenand ammonium nitrogen was commonly deficiency. Available P was deficient insoutheastem and Jianghan Plain while at middle-low or low level in north and middleregions. Available K in southeastern was more deficient than that in the north, while Kwas at middling level in middle region and Jianghan Plain. Available Ca, Mg, S, Fe, Mn,Cu were at rich level in these four regions. Available Zn in southeastern was moredeficient than that in the middle, while was at suitable level in north region and JianghanPlain. Available B was mostly lower in the four regions. Available Mo was deficient insoutheastern and middle regions. Available Si was at suitable level in these four regions.The results indicated that soil N, P and K deficiency was the main limiting factors inHubei for rice planting.(2) The change trend of main nutrients were summarized which would offer basis forsoil fertility improvement and nutrients management. The results showed that the soil pHwas changed from high to low in the regions from north to south. The paddy soil fromalluvial deposit parent material in Jianghan Plain was neutral or alkali. Soil organic matter,total nitrogen, available nitrogen was changed from high to low from south to northregion, and the three items in Jianghan Plain was the most highest in the four regions. Available P as well as available K was changed from high to low from north to south.Available Ca, Mg, Zn and Si were changed from low to high from south to north.Furthermore, available Ca, Mg, S, Zn, Mo, Si was obvious lower in southeastern than thatin other three regions.(3) The relationship among the test results by general test (GT), ASI and M3 methodwas studied. The results of correlation analysis showed that available P, K, Ca, Mg, S, Fe,Mn, Cu and Zn by GT had significantly positive correlation with that by ASI method atP＜0.01 level, while available N and B by GT had no any relationship with that by ASI.Available P, K, Ca, Mg, S, Fe, Mn and Zn by GT had significantly positive correlationwith that by M3 method at P＜0.01 level, and available Cu and Zn by GT had significantlypositive correlations with that by M3 method at P＜0.05 level, while available B had noany relationship by the two methods. Available P, K, Ca, Mg, S, Fe and Zn by M3 hadsignificantly positive correlation with that by ASI at P＜0.01 level, and available Mn andCu by M3 just had positive correlations with that by ASI, while available B had no anyrelationship by the two methods.(4) The advantage and disadvantage of the three chemical analysis methods wasevaluated. The soil nutrient status which were determined by chemical analysis methodswere confirmed through the pot experiments and field trial. Comparison to the potexperiments and field trial, chemical analysis methods had advantages such as directness,speediness and convenience, as well as results were relatively nicety. Comparatively, M3method was the most rapidness one and GT was the slowest. Among the three testmethods, the evaluation result of available N by ASI method was better than GTconfirmed by crops planting experiments, while M3 can't test soil N content. Theevaluation result of available P and K by ASI was much better than that by GT or M3.The evaluation result of secondary element Ca, Mg and S and microelement Fe, Mn andCu by the three methods had the same conclusion which revealed the nutrients status asthe fact. The evaluation result of available Zn by ASI was the best and M3 was the worstamong the three methods. Available B by GT was the best and M3 was the worst. Theresults indicated that the nutrients abundant and deficient standards for GT method mustbe renewed, that the standards of ASI must be perfected and the standards of M3 methodshould be found according to agricultural condition in China.(5) This research raveled the principle of indicator plant selected in pot experiment.Compare to the results of sorghum and rice pot experiment, rice was a better indicatorplant than sorghum when the field crop is rice. It is suggested that the indicator plant usedin the pot experiment should be the same as that grew in the field. (6) The response of NPK combined fertilization was studied in rice field trials. Theresults showed that yield decreased in CK (no fertilization), -N (PK), -P (NK) and -K (NP)compared with NPK Treatment. The average increment rate of N, P and K fertilizer were45.8%, 13.1% and 11.3%, and the average agronomic efficiency of N, P₂O₅ and K₂Owere 11.7 kg/kg, 12.1 kg/kg and 6.6 kg/kg, respectively. Generally, the increment of thethree nutrients was in the order of N＞P＞K in the main rice regions in Hubei. However, insome fields the order might be N＞K＞P in some area. The field results validated that N, Pand K deficiency are the main limiting nutrient factors in rice cultivation in Hubei at thepresent time.