Effect Water-potassium Coupling On Physiological Characteristics, Yield And Quality Of Soybean

Vegetal biomass constitutes the foundation of seed yield, and plant dry matter accumulation which come from photosynthesis account for 90%-95% in all. Transpiration ensures photosynthesis on the rails. Stoma is both the channels of vapour overflow and the portal of CO2 assimilation. However, potassium fertilizer and soil moisture impact plant photosynthesis, and soil water stress lowers stoma ringent extent and weakens plant photosynthesis; potassium fertilizer regulates the open and close of stoma first, and then regulates plant photosynthesis and transpiration. So diffierent potassium fertilizer and water levels applied in this experiment were to elucidate the effect of water-potassium coupling on physiological characteristics, yield and quality of soybean in order to provide practical agricultural measures for soybean production in Heilongjiang province.Pot experiments were carried out in Hailun Agro-ecological Experimental Station in 2006. In this experiment, five water supply levels and three potassium fertilizer application levels were included in terms of soil water content controlled at vegetative stage(V2-R1), flowering stage(R1-R3) and podding stage(R3-R5), respectively. The purpose is to investigate effects of water supply levels in different growth stages on physiological characteristics, yield and quality of soybean under different potassium fertilizer levels. The methods of each tested index are as follows: (1)Photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration were measured by using a portable CI-301PS photosynthesis system(CID,Inc.,USA); (2) chlorophyll was distilled with ethanol and was determined by the specific absorption coefficients at 663 nm and 645 nm by using spectrophotometry; (3) leaf area was measured by using a portable CI-203PS leaf area system(CID,Inc.,USA); (4) protein content was determined by the Kjaldahl method; (5)The soybean oil was extracted with aether.When soil moisture was controlled at the same growth stage, both soil moisture and potassium ferlizer influenced photosynthetic characteristics of soybean, but soil water content played a more important role than potassium fertilzer. Photosynthesis rate, transpiration rate and stomatal conductance had the similar changes at the same stage, and soil water content had positive effects on them, W4 was the optimum water treatment. Soil water content had positive effect on WUE but potassium fertilizer played the opposite. The WUE of soybean increased and then decreased with the growthing of soybean, the positive effect of soybean WUE showed in the order: flowering stage>poding stage>vegetitive stage. Soil water stress had double edged influences on chlorophyll content which decreased under exceeding drought condition(W1) but increased under mild drought condition(W2). When soil moisture was controlled at the same stage, the coupling of water-potassium fertilizer exerted similar effects on leaf area index to photosynthetic rate. The leaf area index increased with the growthing of soybean in an order of poding stage>flowering stage> vegetitive stage. The plant height developed mainly come from seedling stage to flowering stage, thereafter the increment of soybean plant height were little. When soil water content was controlled at vegetitive stage and flowering stage, biomass distribution of each apparatus showed the order of leaf weight>stem weight>root weight. When soil water content was controlled at podding stage, the order was: seed weight> leaf weight>stem weight>root weight. Soil moisture and potassium fertilizer had impacts on the formation of biomass in different part of soybean, and soil water content had a negative effect on the formation of biomass, W4 level was the optimal soil water treatment. The biomass accumulation of applying potassium fertilizer treatments was superior to other treatments under the same soil water content condition. Coupling of water-potassium influenced shoot dry matter weight more than on root dry matter weight, and the influence on the ratio of root to shoot was the least. Soil water supply had more significant effect on dry matter weight and the ratio of root to shoot than potassium fertilizer application did. The sufficient soil moisture enhanced the accumulation of dry matter, while the ratio of root to shoot decreased with the increase of soil water content.Potassium fertilizer played a vital role in protein accumulation but not in oil accumulation for all the stages. When soil moisture was controlled at different growth stage, soil water content had different influences on protein content. When soil moisture was controlled at vegetative stage, protein content increased with the increase of soil water content under the same potassium fertilizer level. When soil moisture was controlled at flowering stage and podding stage, protein content at W3 level was optimical under the same potassium fertilizer level.The treament with the highest biomass accumulation was not the one of the optimum seed yield. The hightest seed yield of all treaments was combination of W3K3 which increased seed yield by 10.90% than control, and it was the classic treament of all in this experiment. When soil water content was controlled during the vegetative stage, the effect of different treatments on yield decreased in the order of potassium fertilizer >water>water-potassium fertilizer; when the soil water content was controlled during flowering stage and podding stage, the yield difference was mainly attributed to the water supply, while potassium fertilizer and the interaction of water-potassium fertilizer played a little role in yield. The reduction of yield under deficient soil water condition at different stages showed in an order: podding stage> flowering stage>vegetative stage. The contribution of water supply to the yield formation was more central than potassium application in the light of soil water controlled at the same growth stage. Both drought and water logging conditions were found to influence the yield of soybean, in which drought condition reduced the yield more significantly.This reseach found that the sensitive stages of the soybean yield to soil water were flowering and podding stages, while soil water condition had relative small impact on the seed yield of soybean at vegetative stage, so attention should be paid to regulating soil moisture at flowering stage and podding stage, and good irrigation and drainage equipment should be set up. Applying potassium fertilizer at a certain extent may increase the yield of soybean together with suitable water supply, so optimical potassium fertilizer should be applied for agriculture production in terms of soil water condition, and the coupling effect of water-potassium fertilizer should be paid to on soybean growth and development. The availability of potassium became lower at later growth stages of soybean due probably to the transformation of exchangible potassium to non-exchangible potassium when soil water content was higher at early growth stage and lower at later growth stage. Potassium fertilizer should be applied at later growth stages in order to increase the content of available potassium when soil water was sufficient at early growth stage and drought took place at later growth stage. The seed yield did not increase corresponding to the increase of dry matter accumulation under the condition of higher water content and fertilizer application, which might be attributed to the inbalance of development of vegetable organs resulting in suppression of seed yield, it is of great significance to harmonize fertilization with water supply in agriculture production.