| Potassium(K) as one of the essential macroelements during plant growth and development process, participates in many processes of the life activity in rice, involving in plant photosynthesis, CO2 assimilation rate, protein synthesis, cell osmotic adjustment, stomata movement, enzyme activation, organic acid metabolism, stress response, seed quality and yield formation. With the production of high-yield rice varieties, increasing of multiple cropping indexes, imbalance of fertilizer application ratio and shortage of soluble potash resources in China, soil K shows the obvious deficient in paddy soil in South China, which is one of important factor of limiting the rice yield. Under the current production conditions, this study was conducted at field condition to study K nutrition characteristics of main rice varieties under K supplying levels and establish K nutrition diagnosis index, clarify the balanced fertilization of nitrogen(N) and potassium(K) and their interactive effects on rice growth and development, understand the better measures of high-efficient K application at rice-oilseed rape cropping system. This study was aim to provide theoretical references and technical supports for the high-efficient K management and the sustainable development of agriculture in rice production in Southern China, especially in Hubei province. The main results were as follows.(1) Appropriate K amounts significantly increased dry matter and K accumulation of aboveground parts and different organs. The shoot dry matter and K accumulation with the progress of growth days after transplanting could be fitted significantly with ―Logistic growth curve‖. Dry matter and K accumulation presented the single peak variation with growth progress and the average maximum dry matter accumulation and K maximum accumulation rate occurred on 67.8 d and 44.0 d after transplanting. The K application also prolonged 3.0 d of the duration of K rapid accumulation and increased 3.0 kg/(hm2·d) of the K maximum accumulation rate. K application significantly increased K distribution amount at different organs of rice plant, increased the proportion at leaf sheath and stem, while reduced the proportion at leaf and seed parts. K accumulation mainly concentrated from initial tillering stage to heading stage, accounted for 83.6% by the whole growth stage.(2) The potassium content of the 2nd functional leaf blade(LB2) and the ratios of K content between 1st and 4th leaf blade(LBKR1/4) could be all used as indicator for the diagnosis of K nutrition in rice. K contents of leaf blade and leaf sheath were obvious differences on different leaf position of rice main stem. The responses of K content at different leaf position to K application showed the order of lower leaf blade(leaf sheath) > upper leaf blade(leaf sheath), leaf sheath > leaf blade. Significant relation between K content of all parts and K uptake and grain yield was investigated. Using the 95% of optimum yield as the critical value, when K content of LB2 in the initial tillering stage, active tillering stage, effective tillering critical period, jointing stage, booting stage and heading stage were lower than those of 1.34%, 1.58%, 1.98%, 2.09%, 1.33% and 1.27%, K fertilizer should be applied to maintain plant K requirement. In addition, significant exponential relations(P < 0.01) were investigated between LBKR1/4 and plant K uptake and grain yield. Using LBKR1/4 as the diagnosis index could eliminate the differences caused by different growth periods and varieties. When each growth period LBKR1/4 > 1.10, K fertilizer should be applied, otherwise there existed the risk of yield losses.(3) Under the soil K deficient condition, K application significantly increased grain yield by 18.9%. There were great differences in optimum K amounts for different rice varieties, and the variation range was from 67.6 to 164.0 kg K2O/hm2. K2 O absorption of 100-kg seeds of all varieties increased significantly with the increase of K supply levels, ranging of 1.05~1.62 kg at zero K rate and 1.40~3.59 kg from 60 to 240 kg K2O/hm2. K use efficiencies significantly decreased with K fertilizer applied. According to the grain yield levels at K deficiency stress, K use efficiency, yield increase rate and optimum K fertilizer rate, the K efficiency of eight rice varieties was evaluated. The No.4(Huaan 3) and NO.7(Jinyou 527) could be classified by the high yield, high efficiency, high response and easy-meet type varieties. They could be planted at areas of low K supplying soil, achieving the aims to save K resources and high yield by appropriate amount of K fertilizer application.(4) Compared to the NK-free treatment, grain yield increased significantly by 42.2% and 62.9% in two years at the combinations of 180 kg N/hm2 and 120 kg K2O/hm2, at which N- and K- use efficiencies could also reach the better levels. The grain yield increased due to the combined use of N and K fertilizer was attributed to an increase in spikelet per panicle(SP), which was responsible for the greatest direct contribution(1.017) and total contribution(0.920) to grain yield. The interactive effects of N and K fertilization on grain yields and K uptakes were significantly positive over two years. With the increase of K rate and the progress of the growth period, the responses of leaf SPAD to N rate showed the increasing trends, and N deficiency accelerated the senescence of lower leaf blade than upper leaf blade. K deficiency stress resulted in the increasing soluble sugar and then led to increase of specific leaf weight under N-application condition. According to the leaf color of field experiment and the performance of leaf nutrition and physiological status, K deficiency stress did not affect rice color or leaf chlorophyll content under the condition of N deficiency at vegetative growth stage in rice. However, K deficiency stress increased significantly leaf N content and leaf chlorophyll content per weight or per leaf area under the condition of N application, which were attributed to the most probable reasons resulting in leaf dark green by K deficiency, and this phenomenon might be detrimental to plant nitrogen nutrition diagnosis in the early growth stage of rice.(5) K application significantly increased crop yield at different ecological regions for rice-oilseed rape cropping systems. The increase rate of oilseed rape was greater than rice to response to K fertiziliation, and the increase rate increased significantly with progress of planting year. The increase rate showed the order of Qichun(Sandy clay)> Wuxue(loam) > Chibi(Silty clay) > Jingzhou(Silty clay loam) at different sites. Moreover, there was a significant negative correlation(P < 0.05) between yield increase rate and initial soil K contents(exchangeable K and non-exchangeable K). The K apparent balance showed extremely negative(133.0~962.2 kg K/hm2) during the whole system at different site. The ratio of K uptake from K fertilizer increased significantly with increasing K rate. Soil exchangeable K and non-exchangeable K contents were always lower at the treatments of zero K rate than the treatments of higher K rate. At different sites, rice and oilseed rape could achieve higher yield and maintain soil K content of 0~20cm and 20~40cm when 90~180 kg K2O/hm2 applied.(6) For the rice-oilseed rape cropping system, after-effect of K for rice season was more obvious than oilseed rape. Nutrient use efficiency of whole cropping systems were higher at the treatments of K90-90(90 kg K2O/hm2 in rice and 90 kg K2O/hm2 in oilseed rape) and K90-45(90 kg K2O/hm2 in rice and 90 kg K2O/hm2 in oilseed rape) than other K treatments. In general, under the condition of the shortage of K resources, K fertilizer application should follow the principle of decreasing application in oilseed rape, favor application in rice season during rice-oilseed rape cropping system. |
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