Effects Of Potassium Uptakes By Crops On Transformation,Mobilization And Potassium Supplying Capacity Of Soils

Soil potassium (K) plays an important role in increasing crop yields, improving the crop quality and maintaining soil fertility. Research works on K-supplying capacity of soils has become important under current shortage of potash resources in China. This paper studied the movement and transformation of potassium and potassium supplying capacity in different types of soils under crop planting, aiming to provide scientific basis for understanding the mechanism of soil supplying K and reasonable K control. The main results are as followed:1. A pot experiment was carried out to study their potassium (K) supply capacities and K dynamics in different types of soils under ryegrass-rice rotation system. Results showed that both aboveground biomass and K uptake of the crops were the highest in Fluvo-aquic soil (FS), followed by Yellow cinnamon soil (YCS), and Red soil (RS) in the group without K treatment (NP). For the group with K fertilization (NPK), no significant difference (p>0.05) was observed in aboveground biomass among the soils but presented a decreasing order of YCS> FS> RS was in terms of K uptake. Crop biomass in the NPK treatment was55.6%in RS,45.2%in YCS and23.2%in FS higher than that of the NP treatment, respectively. Similarly, K uptake by crop in the NPK treatment was368.8%in RS,66.8%in YCS and74.5%in FS higher than that in the NP treatment, respectively. For the NP treatment, the concentrations of water soluble K and exchangeable K decreased in all the soils during the ryegrass growth season. However, non-exchangeable K decreased significantly in FS, non-exchangeable K in RS and YCS remained almost unchanged in the early season, then rose in the middle season and dropped in the late season. Compared with the NP treatment, soil K was much higher in the NPK treatment, which varied in a similar pattern in all the three soils, regardless of K forms. During the rice growing period, in the NP treatment, water soluble K did not change much in all the soils. Soil exchangeable K declined first and then rose whereas non-exchangeable K showed a reverse trend. For the NPK treatment, soil exchangeable K rose significantly in the early stage, then declined in the middle stage, and turned slightly back again in the late stage. However, soil water soluble K and non-exchangeable K showed a rising trend at first and then a falling trend. To sum up, K consumption was higher in the NP treatment across the soils through the entire period of the rotation, i.e., decreasing both soil water soluble K and exchangeable K and in turn triggering release of non-exchangeable K. Application of K fertilizer would increase the concentrations of water soluble K and exchangeable K and the ratio of K transformed into non-exchangeable K, thus effectively improve K supply capacity of the soil, and eventually increase the yield of ryegrass and rice significantly.2. We collected three typical soils (i.e., RS, YCS and FS) from South China, studying potassium fixation and release characteristics under the basic soil and K-depleted soil (conducted by bio-depletion). Results showed that both amount and rate of K fixation in K-depleted soils were significantly (p<0.05) higher than that of basic soils. There were significantly (p<0.05) negative correlation between K fixation rate and the content of soil available K and K+saturation. However, no significant (p>0,05) correlation was observed between K fixation rate and slow-available K. For both basic soil and K-depleted soil treatments, the amount of K fixed was in the order of RS> YCS> FS, but the cumulative amount of K (i.e., successive extractions with1.0mol/L HTNO3) released by the three soils was in an opposite order. K released by successive extractions with1.0mol/L NH4OAc was highest in YCS but lowest in RS. The accumulation of K released by the K-depleted soils was lower than that of the basic soil. The results revealed that non application of K fertilizer would lead to the depletion of soil K, which would strengthen the soil K fixation ability. Similarly, K depletion would induce the decrease of the soil available K which showed the reduction of soil K-supplying ability.3. Under the condition of crop planting, soil water soluble K in root zone was reduced significantly. Along with plants growing and K uptake, soil exchangeable K and non-exchangeable K were transformed into water soluble K, meanwhile, soil water soluble K, available K, slow available K and2mol/L cold HNO3K moved to the root zoon, the closer from the root zoon, the greater the amount of potassium in non-root zone moved to the root zoon. With the K uptake intensity increased, the transference distance of potassium was increased in non-root zone. Under low intensity of K absorption, the transference distance in RS, YCS and FS were6cm,5cm and5cm for water soluble K,5cm,6cm and5cm for available K,3cm,1cm and5cm for slow available K, and5cm,5cm and5cm for the2mol/L cold HNO3K, respectively. Under middle intensity of K absorption, the transference distance in RS, YCS and FS were6cm,7cm and6cm for water soluble K,6cm,7cm and6cm for available K,5cm,5cm and5cm for slow available K, and6cm,6cm and5cm for the2mol/L cold HNO3K, respectively. Under high intensity of K absorption, the transference distance in RS, YCS and FS were7cm,7cm and8cm for water soluble K,7cm,7cm and8cm for available K,6cm,5cm and6cm for slow available K, and6cm,7cm and7cm for the2mol/L cold HNO3K, respectively.