Nitrogen (N) over-application is a serious problem in intensive agricultural production areas with consequent large N losses and environmental pollution. In contrast to N, potassium (K) application has been neglected in many developing countries and this has resulted in soil K depletion in agricultural ecosystems and prevented increases in crop yields. Nitrogen-potassium interaction is currently a topic of interest in many studies and the focus of this review is K nutrition under varied N regimes. Nitrogen form and application rate and time influence soil K fixation and release, as well as K uptake, transport, cycling and reutilization within crops. High yielding quality crops can be obtained by optimal N: K nutritional ratios. High rates of applications of N and K do not necessarily lead to increased yield increments and may even reduce yield. Yield response to K uptake depends on N nutritional status and the interaction is usually positive when NO 3 − -N is supplied. Antagonism between NH 4 + and K + in uptake was mostly attributed to simple competitive effects in the past while evidence showing mixed-noncompetitive interactions existed. Two components of membrane transport systems for K uptake by plants are a high-affinity K + transport system which is inhibited by NH 4 + and a low-affinity K + transport system which is relatively NH 4 + insensitive. Potassium is highly mobile within plants but its flow and partitioning can change depending on the forms of N supply. NH 4 + nutrition in comparison to NO 3 − -supply results in more K translocation to leaves. A better understanding of the mechanism of N-K interaction can be a useful guide to best nutrient management in agricultural practice in order to achieve high yields with high nutrient use efficiency.

In cotton ( Gossypium hirsutum L.) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied. After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate ( P N ) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply. Decreased leaf P N of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves. Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading. K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues.

There has been a phenomenon in wheat production of attaching importance to nitrogen fertilizer but ignoring potassium fertilizer. Employing nitrogen fertilizer solely results in excessively growing, soft stemmed, wheat, leading to a reduction in kernel yield. Also, the soil hardens and the environment is destroyed. As one of the indispensable elements, potassium has become an important limiting factor in wheat kernel yield increasing. This article studied the effect of potassium on photosynthetic rate, sucrose content, activity of sucrose_phosphate synthase (SPS)—the key enzyme in sucrose synthesis—in flag leaves, and on the sucrose content, activity of sucrose synthase (SS) (the key enzyme in sucrose decomposition), activity of adenosine phosphorate glucose pyrophrylase (ADPGPPase) (the key enzyme in starch formation), and starch accumulation rate of kernels of wheat. The study was carried out in 1999 on an experimental farm of Shandong Agricultural University, Taian,China,using the variety `Lumai 22’which has high yield potential. The experiment set three potassium treatments (K0, K1 and K2); the potassium amounts supplied were 0 kg K2O, 168.75kg K2O, 225.00 kg K2O per hm2 respectively,using KCl as the potassium fertilizer. Each treatment had three replicates. The plot area was 2 m×6 m=12 m2, with sowing on October 11 in 1999. The basic seedling number was 120 per m2. Single stems flowering on the same day were selected and marked using hanging cards during the anthesis period. These marked stems were used as the sample. The results suggest that potassium can prolong the peak period of photosynthetic rate, increase the supply of photosynthetic products in flag leaves, improve the activity of SPS after anthesis, accelerate sucrose synthesis during the early and middle periods of kernel filling in flag leaves, and increase sucrose content in flag leaves. Potassium also enhanced the supply of sucrose in the kernel during kernel filling, increased the activity of SS which favors sucrose decomposition in the kernel, and produces sufficient precursor for starch synthesis; improved the activity of ADPGPPase which favors starch formation; accelerated the rate of starch accumulation during the peak period of starch synthesis, and finally increased spike number, kernel weight and yield in wheat. Among the three treatments, each index had the greatest value in the K1 treatment. So the K1 treatment produced the highest kernel yield.The physiological effects of potassium on yield in wheat were discussed from two points of view, namely, from the point of photosynthetic product supplying intensity in flag leaves and precursor supplying intensity in kernel sink, concentrating on key enzymes. It was considered that potassium could increase kernel weight and yield by increasing the activity of SPS in the flag leaf and increasing the activities of SS and ADPGPPase in the kernel, but the physiological and biochemical mechanisms underlying this action should be investigated further. Furthermore, this article also discussed the reason why the K1 treatment is superior to the K2 treatment. It is possible that root absorption of K+ and NO-3 -N are inter- related, and so an excessive K+ concentration could affect the absorption of NO-3 -N in the root. This would result in an effect on nitrogen absorption and transportation throughout the wheat plant, causing a reduction in wheat yield. The physiological mechanisms behind this effect require further study.

利用冬小麦品种‘鲁麦22’(Triticum aestivum cv. `Lumai 22’)在大田条件下研究了钾素对小麦旗叶蔗糖和籽粒淀粉积累及其有关酶活性的影响。结果表明，钾素有利于提高旗叶光合速率，增强开花后旗叶磷酸蔗糖合成酶活性，提高旗叶中蔗糖的含量；从而提高了灌浆期间籽粒中蔗糖的供应，增强了籽粒中蔗糖合成酶和腺苷二磷酸葡萄糖焦磷酸化酶的活性，加速了淀粉积累速率，提高了粒重和产量。

Abstract The conventional nitrogen (N) rate is 300 kg/ha in cotton production in the field with middle level fertility in the Yangtze River Valley in China. Applications of N are usually split into a pre-plant application (PPA), a first bloom application (FBA), and a peak bloom application (PBA), at percentages of 30%, 40%, and 30%, respectively. However, the facts of little positive yield response with a higher N rate, water nutrition enrichment, and cotton early senescence are universal. The purposes of this study were to understand and determine the cotton yield using a lower N rate but allocating more N to the late growing period (PBA) and to specify the characteristics of cotton growth and biomass accumulation by the alteration. Fixing the N rate at 225 kg/ha and FBA ratio at 40%, the effects of different balances for the remaining 60% N between PPA and PBA on cotton ( G. hirsutum L. var. Huazamian H318) growth, yield, and biomass were studied in field trials (2008 and 2009) and a pot trial (2009). The results showed that the balance of 0% PPA and 60% PBA ratio had a shorter seedling period and a longer flowering and boll setting period, compared to the balance of a higher PPA and lower PBA ratio. Both field and pot trials showed the same trend but significant differences existed among treatments in the pot trial. Cotton lint yield was as high as 1200 kg/ha for PA treatment (0% PPA + 60% PBA), which was significantly higher than any other treatments since it had a higher biomass accumulation speed in both the average (1.3 g/d) and the highest (4.51 g/d) during the fast biomass accumulation period, a higher total biomass (189.7 g/plant) and a higher harvest index (16.82%). These results suggest that allocating more N to PBA should increase cotton biomass, harvest index, and yield. Highlights ? Lower N rate is possible for cotton high yielding by decreasing pre-plant application ratio and increasing peak-bloom application ratio. ? The alteration of N split ratio has a longer reproductive period, a higher speed of biomass accumulation during the fast accumulation period. ? Cotton biomass is correlated to the accumulation speed more than the duration of fast accumulation period. ? Cotton yield is related to the biomass positively after peak bloom, but negatively before peak bloom.

In order to study the effects of different planting densities on nutrition characteristics and yield of cotton, a field experiment was conducted by using five planting densities from 9.0 to 27×10 4 plant/ha. The result shows that the highest yield is 3247.4 kg/ha under the 18.0×10 4 plant/ha. The N, P and K accumulation amounts at the period of boll opening and cotton yields are higher in 18×10 4 and 22.5×10 4 plant/ha. The dynamic changes of N, P and K contents of plant of cotton are decreased with the increase of density. However, the group changes are different, the N, P, K contents of group of cotton are the highest during the initial flowering and boll opening stage since the maximizing came from 15th of August, so nutrition accumulation of the latter stage was very important with the yield, especially nutrition accumulation of group and reproductive organ.

田间小区试验研究了不同栽培密度对棉花植株养分特征及产量的影响。结果表明: 密度为18.0×10 4 株/hm 2 （A3处理）皮棉产量最高，为3247.4 kg/hm 2 ; 吐絮期铃中氮、磷、钾含量以18.0×10 4 株/hm 2 （A3）、22.5×10 4 株/hm 2 （A4）处理积累量较高，与产量一致; 不同密度处理单株氮、磷、钾含量随密度的增大而减小; 群体变化趋势则不同，虽然最高值仍都出现在8月15日，但在盛铃～吐絮期却以A3处理各元素的含量最高。说明后期养分积累对产量的形成具有重要的作用，尤其是植株群体和生殖器官的养分积累量。

Nitrogen application rates of 0, 75, 150, 225, 300 and 375 kg ·hm -2 on dry matter accumulation and distribution as well as the N, P, K uptake and utilization of hybrid cotton were studied under high yield conditions. The results showed that the nitrogen utilization and dry matter content were significantly positive correlated with N, P, K accumulation. The nitrogen can improve the dry matter and N, P, K accumulation. But the effect that applying nitrogen was no longer significant when the nitrogen application rate increased to 300 kg·hm -2 . The analysis of nitrogen content on dry matter accumulation of different organs indicated that nitrogen content was positive correlated with leaves and negative correlated with stems in the middle stage of cotton growth periods and positive correlated with stems in the latter growth stage. The nitrogen content was positively correlated with cotton bud and flower in the middle growth stage while negative in the latter growth stage. When the nitrogen application rate increased to 300 kg·hm -2 , nitrogen decreased the proportion of N, P, K and dry matter distributed to reproductive organs and increased the proportion of leaves and stems. The vegetative growth of the hybrid cotton was excessively vigorous. In this experiment, applying the nitrogen of 300 kg·hm -2 had the highest seed cotton yield which was 1.66％ higher than the nitrogen of 225 kg·hm -2 , but there was no significant difference. When nitrogen rate increased to 375 kg·hm -2 , the seed cotton yield decreased by 2.23％ and 3.92％ compared with N 300 kg·hm-2 and 225 kg·hm -2 , respectively. The nitrogen utilization decreased distinctly while the phosphorus and potassium utilization increased with the more nitrogen fertilizer added.

在高产条件下，研究了施氮0、75、150、225、300和375 kg·hm -2 对杂交棉干物质积累、分配和氮、磷、钾的吸收、分配与利用的影响，结果表明：施氮量与杂交棉的干物质和氮、磷、钾的积累间均表现显著正相关，増施氮肥促进了杂交棉的干物质和氮、磷、钾的积累，但是当施氮量增加到300 kg·hm -2 后，促进效果不显著。施氮量与各器官干物质、氮、磷、钾的分配比例关系：与叶片呈显著或极显著正相关，在棉花生育中期与茎呈负相关，生育后期呈正相关，在棉花生育中期与蕾、花、铃呈显著正相关，生育后期呈显著负相关。施氮量增到300 kg·hm -2 后，棉花生育后期干物质和氮磷钾在生殖器官的分配比例明显下降，在茎叶的分配比例明显提高，表现营养生长过旺。氮积累和分配与磷、钾积累和分配间表现很好的正相关，从产量水平看，以每公顷施氮300 kg的子棉产量最高，比施氮225 kg的增产1.66％，增产不显著。施氮量达375 kg·hm -2 时，子棉产量比300 kg·hm -2 的减产3.92％、比225 kg·hm -2 减产2.23％。随施氮量增加，氮肥利用率明显下降，而磷和钾的利用率提高。

在大田栽培条件下,分别在长江流域下游棉区(江苏南京)和黄河流域黄淮棉区(河南安阳)设置棉花氮素水平试验,定量研究氮素水平对花后棉株生物量、氮素累积特征及氮素累积利用率动态变化的影响,结果表明:棉株总生物量和氮素累积量随花后棉株生育进程的动态变化符合S型曲线,安阳、南京试点分别以360kg·hm-2、240kg·hm-2氮素水平的总生物量、氮素累积最多,其动态累积模型的特征参数值最为协调,皮棉产量最高.因此,可以通过改变施肥量来调节初花后棉株生长特征值,从而获得高产.棉株氮素累积利用率随初花后棉花生育进程的推进,呈现为不规则的S型曲线变化趋势,计算两试点的氮素累积利用率、瞬时利用率,安阳试点以360 kg·hm-2的施氮水平为最优,南京以240 kg·hm-2最高;施肥过多不仅利用率低,而且易造成营养器官比例加大,棉株虽可获得较大的干物质和氮素累积,但不能适时向生殖器官转移,皮棉产量降低.

In this paper, field experiment of different nitrogen application levels for cotton was conducted both in Nanjing of Jiangsu Province and in Anyang of Henan Province. The quantitative dynamic models of critical nitrogen uptake rate and demand of cotton after flowering were established, based on the models of crop critical nitrogen concentration dilution curve and dry matter accumulation curve. The results showed that in Nanjing and Anyang, the maximum critical nitrogen uptake rate of cotton was 5.3 kg·hm -2 ·d -1 and 4.4 kg·hm -2 ·d -1 , respectively, and appeared at 42 days after flowering. The 23～59 days and 23～61 days after flowering were the periods of rapid nitrogen accumulation in cotton plant, and the critical nitrogen demand per day was higher in Anyang than in Nanjing. By comparing the nitrogen uptake rate and accumulation amount with their critical values, the appropriate N application rate for cotton was slightly lower than 360 kg·hm -2 in Anyang, and 240 kg·hm -2 in Nanjing. 26% and 27% of total fertilizer nitrogen should be applied as basal, and the supplemental nitrogen should be applied at 22 days after flowering. Because the model in this paper was established on the basis of critical nitrogen concentration model and linked to the cotton aerial biomass rather than time, it had a sound eco- physiological basis, and was consequently superior to other models. It also offered a tool to determinate the nitrogen application rate for cotton in different ecological regions.

在大田栽培条件下，于江苏南京和河南安阳两个生态区设置棉花氮素水平试验，基于作物临界氮浓度稀释模型和干物质动态累积模型，建立了棉花花后动态临界氮吸收速率、临界氮需求量的定量化模型.结果表明，两生态区的临界最大氮吸收速率均出现在花后42 d，分别为5.3和4.4 kg·hm -2 ·d -1, 临界快速氮累积期分别在花后的23～59 d和23～61 d，安阳的最大临界日需氮量明显大于南京.根据模型得到：安阳生态区适宜施氮量在240～360 kg·hm -2 之间,且360 kg·hm -2 条件下其氮累积接近临界需求，南京生态区240 kg·hm -2 施氮量的氮累积与临界值相近.两区域基肥施用量分别占总施肥量的26%和27%，且适宜的追肥时间应在花后22 d左右.由于模型的建立是基于不同氮处理试验，有合理可靠的生理依据，为定量确定不同气候区域的动态施肥量提供了理论依据.

This study evaluated the physiological effects and biochemical characteristics of functional axial leaf and different position sympodial leaf as affected by applying different levels of nitrogen fertilizer(0 kg/ha Low N;189.50 kg/ha Middle N;395.0kg/ha High N) using Bt-transgenic hybrid cotton variety 33B.The differences of leaf area index and leaf physiological index(chlorophyll,dissoluble protein and MDA) were studied with different levels of nitrogen across the growing season were studied using a randomized block design.The leaves were divided into four classes according to their positions: stem leaves,top sympodial leaves,middle sympodial leaves,lower sympodial leaves.The main results were as follow:(1) Under the conditions of this experiment,full boll stage was the turning point of every index,indicating that this was the starting phase of leaf senescence;(2) The content of chlorophyll and dissoluble protein of the leaf decreased significantly and MDA content increased when nitrogen was deficient,which accelerated the process of senescence;(3) Compared with normal level of nitrogen,excessive nitrogen would increase senescence rate of lower sympodial leaves and aggravate the trend of senescence for the whole plant.The top sympodial leaves were most sensitive to nitrogen deficiency.Therefore,proper nitrogen applications would delay cotton leaf senescence.

通过3个氮素(N)水平(低氮0.kg/hm 2 、中氮189.50.kg/hm 2 、高氮395.0.kg/hm 2 )处理,研究棉花主茎功能叶和不同部位果枝叶衰老过程中的生理生化变化特征。以转基因抗虫棉33B为材料,采用随机区组设计,研究棉花生育期内不同施氮水平下棉花叶面积指数和叶片(主茎功能叶和果枝叶)生理指标(叶绿素含量、可溶性蛋白质含量和丙二醛含量)的差异,分析氮素影响不同部位叶片衰老的效应。结果表明:1)在本试验条件下,盛铃末期为各指标变化的转折点,表明这个时期是叶片生理功能衰老的起始期;2)氮素营养缺乏会引起整体叶片的叶绿素、可溶性蛋白质含量大幅度下降,丙二醛含量升高,加速了叶片的衰老进程;3)当氮素过多时,会加速下部叶片的衰老,上部果枝叶对氮素的缺乏最敏感,因此,施入适量的氮肥,可获得延缓整株叶片衰老的效果。

Field experiments were conducted in Anyang and Nanjing, the typical representatives of ecological regions in the Yellow River Valley and the lower reaches of Yangtze River Valley in China, to quantitatively analyze the spatiotemporal variability of biomass accumulation of the fruiting branch of cotton variety Nucotn 33B at its flower and boll stage under effects of 0, 120, 240, 360, and 480 kg N·hm -2 (marked as N 0 , N 1 , N 2 , N 3 , and N 4 , respectively). The results indicated that both in Nanjing and in Anyang, the temporal variability of biomass accumulation of vegetative and reproductive organs at different positions of fruiting branch could be described by Logistic equation, but the spatial variability was obviously different. Under the nitrogen application rate of 360 kg·hm -2 in Anyang and of 240 kg·hm -2 in Nanjing, the biomass accumulation had the characteristics of earlier starting date, shorter duration, and maximal speed of rapid increase. These nitrogen application rates could accelerate the biomass accumulation to benefit the high lint yield and fiber quality, while excess or deficient nitrogen supply was disadvantageous to the biomass accumulation of fruiting branch. Therefore, it could be possible to apply appropriate amount of nitrogen to regulate the growth eigenvalues of different positions fruiting branch at its speed growth stage to obtain high lint yield and fiber quality.

试验在黄河流域黄淮棉区的河南安阳和长江流域下游棉区的江苏南京棉花大田进行， 氮素设0（N 0 ）、120（N 1 ）、240（N 2 ）、360（N 3 ）、480（N 4 ） kg·hm -2 5个水平，定量分析了不同施氮量对美棉33B花铃期棉花果枝生物量累积时空变异特征的影响.结果表明： 不同施氮量下，两试验点棉株不同果枝部位营养器官、生殖器官、生物量累积时间变异特征均表现为Logistic曲线，空间变异特征存在明显差异.安阳点360 kg·hm -2 施氮量、南京点240 kg·hm -2 施氮量处理具有快速增长期起始时间早、持续时间短、最大速率大等特征，说明该施氮量水平有利于棉花生物量的快速累积，以形成较高的产量与品质；而施氮量过多或不足均不利于棉株不同果枝部位生物量的累积.可以通过不同的施氮量来调节棉株不同果枝部位快速生长期的生长特征值，以提高棉花的产量和品质.

综述了近50年来我国棉花主产区钾肥的增产作用及其变化趋势、增产效应及施钾技术,阐述了钾对棉花的营养作用、抗性及品质方面的影响.钾肥对棉花的增产效应因不同的植棉区和不同的年代而不同.近年来,随着化学钾肥的推广与施用量的增加,某些棉区钾对棉花的增产作用在逐渐降低.因此,化学钾肥施用的必要性、施用期及施用量原则上应根据土壤钾素丰缺状况及棉花的需肥规律而定.