Effects of different densities of mixed-cropping on 13C-photosynthate distribution and grain yield of maize.

To explore the effects of different densities of mixed-cropping on 13C-photosynthate distribution and grain yield of maize, we measured photosynthetic characteristics, 13C-photosynthate distribution, dry matter accumulation, and grain yield under different planting densities (LD, 67500 plants·hm-2 and HD, 97500 plants·hm-2) under mixed-cropping (M, 1:1, 2:2) and monoculture of Zhengdan958 (ZD) and Denghai605 (DH). The results showed that with the increases of planting density, grain yield, 13C-photosynthate allocation to grain, dry matter accumulation, and leaf area index (LAI) increased, but the chlorophyll content and net photosynthetic rate decreased. No significant difference was observed between the monoculture and mixed-cropping at the density of 67500 plants·hm-2. However, at 97500 plants·hm-2, LAI, chlorophyll content, net photosynthetic rate and dry matter accumulation in mixed-cropping were higher than that in monoculture. Mixed-cropping promoted the transport of dry matter from the vegetative organs such as stem to the grain and the distribution of 13C-photosynthates to grain. Grain yield of summer maize significantly increased in mixed-cropping due to the increase of 1000-grain mass. Under high plant density, the mixed-cropping could enlarge photosynthetic area, maintain higher net photosynthetic rate, increase dry matter accumulation, improve the distribution of dry matter, promote the distribution of 13C-photosynthates to grains and thus increase the grain yield. Our results indicated that mixed-cropping could significantly increase the yield of close planting summer maize in Huang-Huai-Hai Plain.

[The interactive effects of water and nitrogen addition on ammonia volatilization loss and yield of winter wheat.] / 水氮互作对冬小麦田氨挥发损失和产量的影响.

An experiment with winter wheat of Shimai 15 and treatments of two types of fertilizers (organic manure, M; urea, U), two amounts of nitrogen application (180 kg·hm-2, M1U1; 90 kg·hm-2, M2U2), two irrigation levels (500 mm, W1; 250 mm, W2) was carried out in the lysimeters in 2015-2017. The results showed that ammonia volatilization was substantial after fertilization and irrigation. The dynami of ammonia volatilization during two years was similar. The process of ammonia volatilization after fertilization lasted for seven days. In 2015-2016, the total amount of ammonia volatilization ranged from 13.36 to 46.04 kg·hm-2, and the loss rate of ammonia nitrogen ranged from 8.9% to 41.1%. The total amount of ammonia volatilization in 2016-2017 ranged from 14.78 to 52.99 kg·hm-2, and the ammonia nitrogen loss rate ranged from 9.2% to 45.8%. During the two years, the highest loss of ammonia volatiles occurred in W2U1, the highest loss rate of ammonia volatilization occurred in W2U2. Ammonia volatilization loss rate significantly decreased under appropriate water and nitrogen management. Ammonia loss under the application of urea was about 2-3 times of organic manure. The highest yield occurred in W1M1 during the two growing seasons. The type of fertilizer, the amount of irrigation and nitrogen applied interactively affected the yield of winter wheat. As for the increases of production, organic manure was better than urea. Under the experimental condition, the best treatment was irrigation amount of 500 mm and application of organic manure with about 180 kg·hm-2 of N fertilizers, which could be applied in practice for wheat production in Huang-Huai-Hai region.

[Effects of light intensities after anthesis on the photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize (Zea mays L. )]. / èŠ±ç²’æœŸå ‰ç §å¯¹å¤çŽ‰ç±³å ‰åˆç‰¹æ€§å’Œå¶ç»¿ä½“è¶ å¾®ç»“æž„çš„å½±å“.

We examined the changes of photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize in response to different light intensities in the field, with the summer maize hybrid Denghai 605 as experimental material. Two treatments of both shading (S) and increasing light (L) from flowering to physiological maturity stage were designed, with the ambient sunlight treatment as control (CK). Under shading treatment, poorly developed thylakoid structure, blurry lamellar structure, loose granum, large gap between slices and warping granum were the major characteristics in chloroplast. Meanwhile, photosynthetic rate (Pn), transpiration rate, stomatal conductance, chlorophyll content, and actual photo-chemical efficiency (ΦPSII) decreased, whereas the maximal photochemical efficiency and non-photochemical quenching increased, which resulted in decreases in grain yield under shading treatment. However, a better development was observed in chloroplasts for L treatment, with the number of grana and lamellae increased and lamellae arranged compactly. In addition, Pn and ΦPSII increased under L treatment, which increased grain yield. The chloroplast arrangement dispersed in mesophyll cells and chloroplast ultrastructure was destroyed after shading, and then chlorophyll synthesis per unit leaf area and photosynthetic capacity decreased. In contrast, the number of grana and lamellae increased and lamellae arranged compactly after increasing light, which are beneficial for corn yield.

[Effects of water conditions and controlled release urea on yield and leaf senescence physiological characteristics in summer maize.] / ä¸åŒæ°´åˆ†æ¡ä»¶ä¸‹æŽ§é‡Šå°¿ç´ å¯¹å¤çŽ‰ç±³äº§é‡å’Œå¶ç‰‡è¡°è€ç‰¹æ€§çš„å½±å“.

In an soil column experiment with Zhengdan 958 (a summer maize cultivar planted widely in China), treatments of three water levels,severe water stress W1 which the soil moisture kept (35±5)% of the field capacity, mild water stress W2 which was (55±5)%,normal water W3 which was (75±5)%, and four levels of controlled release urea fertilizer (N0, N1 was 150 kg N·hm-2,N2 was 225 kg N·hm-2 and N3 was 300 kg N·hm-2) were included to study the interactive effects of water and controlled release urea on yield and leaf senescence characteristics of summer maize. The results showed that the coupling of water and controlled release urea had significant effects on increasing yield, delaying the senescence and keeping the high efficiency of the functional leaves. Under the same nitrogen condition, yield, LAI, chlorophyll content and the activities of SOD, POD, CAT and soluble protein content in summer maize ear leaf were significantly increased with more water supplying, and the content of MDA decreased significantly. Under the condition of the same moisture, these indicators were also significantly increased with the increasing nitrogen application and MDA content was reduced significantly. However, these indicators (except MDA) of W3N3, W3N2 and W2N3 treatments were maintained at a higher level and the MDA content was lo-wer compared with other treatments despite the fact that there were no significant difference among these three treatments, which indicated that the interactive effects of water and controlled release urea had an important role in maintaining the function of ear leaf, delaying the leaf senescence, and was beneficial to the photosynthates production and obtaining higher yield of summer maize. Integrating the yield, LAI, chlorophyll content, various protective enzymes activity, MDA and soluble protein content, controlled release urea application rate of 225 kg N·hm-2 was the best treatment as the soil moisture content was (75±5)% of field capacity. Continuous increase in the nitrogen application could not enhance the activities of protective enzymes, oppositely, it could cause the decline of protective enzymes activities and the increase of MDA content rapidly and speed up plants translation to senescence, which was not conductive to the efficient use of nitrogen. We suggested that coupling controlled release urea application rate of 300 kg N·hm-2 with soil moisture content of (55±5)% of field capacity was optimum.

[Effects of different cultivation practices on composition, carbon and nitrogen distribution of soil aggregates in farmlands.] / ä¸åŒæ ½åŸ¹ç®¡ç†æ¨¡å¼å¯¹å†œç”°åœŸå£¤å›¢èšä½“ç»„æˆåŠå ¶ç¢³ã€æ°®åˆ†å¸ƒçš„å½±å“.

The long-term experiments were conducted at two locations with different soil fertility. There were four treatments, including super high-yielding cultivation treatment (SH), high-yielding and high efficiency cultivation treatment (HH), local farmer's practice (FP), and control (CK), respectively. The field experiments were established to study the effects of different cultivation practices on composition, carbon and nitrogen distribution of tillage layer soil aggregates in different soil fertility, with the aim of proposing technological approaches to enhance soil fertility and achieve the sustainable development of increasing yield and efficiency in wheat-maize ecosystem. The results indicated that compared with treatments in low soil fertility (LSF), same treatments in high soil ferti-lity (HSF) had the higher mean mass diameter and geometric mean diameter, contents of organic carbon and total nitrogen, and lower fractal dimension in dried soil aggregates at soil tillage layer, which was beneficial to the formation and stability of large aggregate. Optimizing application of NPK fertilizers and the application of combined chemical fertilizer with organic fertilizer could increase the diameter of soil aggregate, reduce the fractal dimension of aggregate and promote the formation and stability of large aggregates, and the effect on HSF was greater than that on LSF; also they could improve the content and distribution of organic carbon and total nitrogen in large soil aggregate, the contribution rate to >5 mm aggregate in LSF was greater than in HSF, while the contribution rate to 5-0.5 mm aggregates in HSF was greater than in LSF.

[Effects of long-term mixed application of organic and inorganic fertilizers on canopy apparent photosynthesis and yield of winter wheat].

A field experiment was conducted using the winter wheat (Triticum aestivum) variety Shimai 15. The source of organic nitrogen was cow manure, and four fertilization treatments were included, i.e., no N fertilizer application, single application of urea, single application of cow manure, and mixed application of urea and cow manure. The effects of different applications of inorganic and organic nitrogen on canopy apparent photosynthesis (CAP), photosynthetic rate of flag leaves (Pn), leaf area index (LAI), florescence parameters and grain yield of winter wheat were determined. The results showed that urea had the largest effect on the early growth period, as at this stage the CAP, Pn and LAI of the single application of urea were the highest, which was followed by the mixed application and the single application of cow manure. However, 10 days after anthesis, the single application of cow manure and the mixed application delayed the leaf senescence process when compared with the single application of urea. This could be due to the two treatments having higher anti-oxidant enzyme activity and promoting a longer green leaf duration, which could maintain a higher photosynthetic capability. What' s more, the mixed application had a better performance and got the highest grain yield. Consequently, the mixed application of organic and inorganic fertilizers could delay leaf senescence and maintain a better canopy structure and higher photosynthesis capability at the late grain filling stage, which resulted in a higher grain yield.

[Effects of sowing depth on seedling traits and root characteristics of summer maize].

Two summer maize hybrids, Zhengdan 958 (ZD958) and Xianyu 335 (XY335), were used as experimental materials. 4 sowing depths (3, 5, 7 and 9 cm) and uneven sowing depth (CK) were designed under sand culture and field experiments to investigate the effects of sowing depth on seedling traits and root characteristics of summer maize. The results showed that the seedling emergence rate gradually decreased and seedling emergence time gradually lengthened as the sowing depth increased. Compared with the sowing depth of 3 cm, the seedling emergence rates of ZD958 and XY335 sown at the depth of 9 cm were reduced by 9.4% and 11.8%, respectively, and the seedling emergence duration was prolonged 1.5 d. With the increasing sowing depth, the seedling length and uniformity decreased significantly, the mesocotyl length increased significantly, while the coleoptile length had no significant difference; the primary radicle length gradually decreased, the total length of secondary radicle gradually increased, and the total root length had no significant difference; the total dry mass of seedling and mesocotyl increased significantly, and the total root dry mass had no significant difference. With the increasing sowing depth, the soluble sugar content in each part of seedling increased and the amount of nutritional consumption of germinating seeds increased, the seedling root growth rate increased, but the root activity decreased, and the number of total nodal root and nodal layers increased. With the increasing sowing depth, harvested ears per unit area were reduced by decreased seedling emergence rate and seedling vigor, thus influenced the yield. In addition, uniform sowing depth could improve the canopy uniformity and relative characteristics, then increase the yield.

[Characteristics of farmland eco-environment at the intercropping stage of maize intercropped with winter wheat and their effects on seedling growth of summer maize].

To study the farmland eco-environment of intercropping maize with wheat at the intercropping stage and its influence on maize seedling growth, two summer maize cultivars, Zhengdan 958 and Denghai 661, were either intercropped with wheat or directly seeded. The result demonstrated that there was little difference for the soil water content of the farmland between the two cultivation methods. The highest soil temperature of intercropped maize was 4.8-5.2 °C lower than the soil temperature of directly-seeded maize, and the lowest temperature of the intercropped maize was 1.4-1.7 °C lower. But, the temperatures for both planting methods met the requirement for seed germination. Light intensity on the ground surface of the intercropped maize was 4.4%-10.6% less than natural light, and insufficient light was the main reason for the weak and late seedling. Compared to the directly-seeded maize, the speeds of seed germination and accumulation of dry matters of the intercropped maize were relatively slow. On the whole, the seedling of intercropped maize was not strong, which presented small leaves, short height and low chlorophyll content. The restraint on the growth of intercropped maize was enhanced with the extension of intercropping period. For farm planting, direct-seeding could improve the seed germination and seedling growth of summer maize.

[Effects of tillage at pre-planting of winter wheat and summer maize on leaf senescence of summer maize].

This study explored the effects of different tillage treatments at pre-planting winter wheat and summer maize on leaf senescence physiological characteristics of summer maize in double cropping system. Zhengdan 958 was used as experimental material. Three tillage treatments, including rotary tillage before winter wheat seeding and no-tillage before summer maize seeding (RN), mold- board plow before winter wheat seeding and no-tillage before summer maize seeding (MN), and moldboard plow before winter wheat seeding and rotary tillage before summer maize seeding (MR), were designed to determine the effects of different tillage treatments on leaf area (LA) , leaf area reduction, photosynthetic pigments content, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities and malondialdehyde (MDA) content in ear leaves of summer maize after tasselling (VT). LA of MN and MR were higher than that of RN from VT to 40 days after tasseling (VT + 40) and LA reduction of MR was the highest after VT + 40. As for MR, MN and NT, the photosynthetic pigments content got the maximum value at 20 days after tasselling (VT + 20) and then decreased, following the change of unimodal curve. At VT + 20, the contents of chlorophyll a in MR and MN were increased by 11.4% and 9.7%, the contents of chlorophyll b in MR and MN were increased by 14.9% and 15.9%, compared with RN. The soluble protein content in ear leaves decreased following the growth process in all treatments, and that of MR and MN remained 11.5% and 24.4% higher than that of RN from VT to VT + 40. SOD, CAT and POD activities of three treatments got the maximum values at VT + 20 and then decreased, following the change of unimodal curve. MDA content increased following the growth process in all treatments and that of RN always remained at high levels. Grain yields of MN and MR were 24.0% and 30.6% greater than that of RN, respectively. Grain yield of MR was 5.2% higher than that of MN. In conclusion, the ability of leaf senescence resistance of MN was improved, which was helpful to increase the yield of summer maize.

[Effect of light from flowering to maturity stage on dry matter accumulation and nutrient absorption of summer maize].

Using Denghai 605 (DH4605) as the experimental material, shading (S) and increasing light (L) treatments from flowering to maturity stage were designed in a field experiment to explore effects of light on dry matter accumulation and nutrient absorption of summer maize. Results showed that grain yield, dry matter accumulation and nutrient absorption decreased significantly after shading but increased after increasing light. Yields in S treatment from 2011 to 2013 were reduced by 59.4%, 79.0% and 60.6% compared to those in CK, while that in L treatment were increased by 16.3%, 12.9% and 6.8%, respectively. The relative N and P absorption increased to a certain extent because of the greater effect of shading on dry matter accumulation than that of N and P absorption. After shading, K absorption of whole plant corn decreased significantly to a greater extent than that of dry matter accumulation decrease. The proportion of nutrient allocated to grains decreased significantly after shading. Dry matter accumulation and N and P absorption rates increased significantly after increasing light, and effects of increasing light on N and P absorption were greater than that of dry matter accumulation. Nutrient accumulation and the proportion allocated to grain increased significantly after increasing light.

[Effects of irrigation and fertilization on soil microbial properties in summer maize field].

In order to investigate the effects of different irrigation and fertilization on soil microbial properties of summer maize field, we used ZN99 with high nitrogen use efficiency as the test material. The experiment adopted the split plot design which included two irrigation levels (526 mm and 263 mm) as the main plots, three fertilizer types (U, M, UM) and two fertilizer levels (N 100 kg . hm-2 and 200 kg . hm-2) as the subplots. The results showed that the irrigation level affected the regulating effects of fertilizer on soil microbial biomass (carbon and nitrogen) and microbial di- versity. The organic fertilizer application must be under the sufficient irrigation level to increase the soil MBC (14.3%-33.6%), MBN (1.8-2.3 times) and abundance significantly. A moderate rate of irrigation, higher rates of organic fertilizer application or organic manure combined with inorganic fertilizer could increase the nitrogen-fixation species and quantity of Firmicutes, γ-Proteobacteria and α-Proteobacteria in the soil. Under the same N level, there was no significant difference of grain yield between organic manure and inorganic fertilizer treatments. Considering sustainable production, proper organic manure application with moderate irrigation could increase the quantity of the soil microbial biomass and microbial diversity, and improve the capacity of soil to supply water and nutrients.

[Effects of shading on endogenous hormones regulation in kernel development of summer maize in the field].

Taking 3 maize hybrids, Zhenjie 2 (ZJ2), Denghai 605 (DH605) and Zhengdan 958 (ZD958) as test materials, the effects of shading on the physiological function of endogenous hormones during grain formation of summer maize were investigated in the field. The ambient sunshine treatment was used as the control (CK) and 3 shading treatments with a shading degree of 60% were designed in growth periods ranging from tasseling to maturity (S1), from jointing to tasseling stage (S2) and whole growing period (S3), respectively. Results showed that the total floret number, filament number and pollination floret number decreased after shading in comparison with CK, and aborted seeds increased accordingly. The kernels per ear showed an order of CK > S2 > S > S3, and those of S1, S2 and S3 were 18.9%, 43.7% and 80.8% lower than that of CK. The IAA, GA and ZR contents of normal grain in the shading treatments were lower than in CK, while the ABA content was opposite. The same hormone change with grain growth in all treatments presented a similar trend. Compared to normal grains, the maximum value of IAA content in aborted grains shifted from the 20th day to the 10th day after pollination, with less IAA accumulation and rapid reduction, and the contents of GA and ZR decreased significantly, while that of ABA was still high at the 20th day after pollination. Therefore, the effects of shading on hormone contents in grains might lead to grain abortion and yield reduction.

[Effect of waterlogging on leaf senescence characteristics of summer maize in the field].

Taking two summer maize hybrids Zhengdan 958 (ZD958) and Denghai 605 (DH605) as experimental materials, a field experiment was conducted to explore the effects of waterlogging for different durations (3 and 6 days) on leaf senescence characteristics of summer maize at the three-leaf stage (V3), six-leaf stage (V6), and 10 days after the tasseling stage (10VT). Results showed that superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities and soluble protein content decreased significantly after waterlogging. However, the content of malondialdehyde (MDA) increased significantly by 35.3% and 34.1% for DH605 and ZD958, respectively. The leaf chlorophyll content and grain yield of summer maize decreased significantly after waterlogging. The grain yields of DH605 and ZD958 after waterlogging for 6 days at V3 were most seriously affected, which were decreased by 32.1% and 35.2%, respectively. Overall, the summer maize was most susceptible to the effect of waterlogging at V3, followed by V6 and 10VT, and the influence extent increased with the increase of waterlogging duration.

[Effects of row spacing on canopy structure and grain-filling characteristics of high-yield summer maize].

Using two summer maize (Zea mays L.) varieties Zhengdan 958 and Xianyu 335, a field experiment was conducted to study the regulatory effects of row-spacing (equidistant row and narrow-wide row) and plant-spot spacing arrangement (1 plant per spot, 2 plants per spot, 3 plants per spot) on grain yield components, canopy structure and photosynthetic characteristics after anthesis under plant population density 7.5 x 10(4) plants x hm(-2). Moreover, the characters of grain-filling were simulated by Richards' model. The results suggested that yield, dry matter accumulated, crop growth rate, grain-filling rate, canopy photosynthesis capacity were higher under wide-narrow row than under equidistant row, and were higher for 2 plants per spot than for 1 or 3 plants per spot. The highest maize yields (13.12 and 13.72 t x hm(-2) for Zhengdan 958 and Xianyu 335, respectively) were observed under wide-narrow row with 2 plants per spot. Under this pattern, internal illumination condition of the canopy, net photosynthetic rate and leaf area index were improved, and the contradiction between the plant individual and group was alleviated. Meanwhile, grain-filling capacity was promoted and accumulated amount of dry matter was elevated ultimately. It was concluded that wide-narrow pattern with 2 plants per spot is an effective cultivation pattern to increase maize yield in Huang-Huai-Hai Plain.

Exogenous calcium alleviates photoinhibition of PSII by improving the xanthophyll cycle in peanut (Arachis hypogaea) leaves during heat stress under high irradiance.

Peanut is one of the calciphilous plants. Calcium (Ca) serves as a ubiquitous central hub in a large number of signaling pathways. The effect of exogenous calcium nitrate [Ca(NO3)2] (6 mM) on the dissipation of excess excitation energy in the photosystem II (PSII) antenna, especially on the level of D1 protein and the xanthophyll cycle in peanut plants under heat (40°C) and high irradiance (HI) (1 200 µmol m(-2) s(-1)) stress were investigated. Compared with the control plants [cultivated in 0 mM Ca(NO3)2 medium], the maximal photochemical efficiency of PSII (Fv/Fm) in Ca(2+)-treated plants showed a slighter decrease after 5 h of stress, accompanied by higher non-photochemical quenching (NPQ), higher expression of antioxidative genes and less reactive oxygen species (ROS) accumulation. Meanwhile, higher content of D1 protein and higher ratio of (A+Z)/(V+A+Z) were also detected in Ca(2+)-treated plants under such stress. These results showed that Ca(2+) could help protect the peanut photosynthetic system from severe photoinhibition under heat and HI stress by accelerating the repair of D1 protein and improving the de-epoxidation ratio of the xanthophyll cycle. Furthermore, EGTA (a chelant of Ca ion), LaCl3 (a blocker of Ca(2+) channel in cytoplasmic membrane), and CPZ [a calmodulin (CaM) antagonist] were used to analyze the effects of Ca(2+)/CaM on the variation of (A+Z)/(V+A+Z) (%) and the expression of violaxanthin de-epoxidase (VDE). The results indicated that CaM, an important component of the Ca(2+) signal transduction pathway, mediated the expression of the VDE gene in the presence of Ca to improve the xanthophyll cycle.

Optimisation of antioxidant peptide preparation from corn gluten meal.

BACKGROUND: Corn gluten meal, containing approximately 600 g kg(-1) protein, is a main by-product of corn wet milling. The annual output of corn gluten meal in China is over 840 000 tons. However, it is difficult to utilise corn gluten meal in the food industry because of its low water solubility and amino acid imbalance. In the present study, corn gluten meal was hydrolysed by different proteases to produce hydrolysates with antioxidant activity in order to increase its value. The hydrolysis conditions were optimised by multiple linear regression and response surface methodology. Furthermore, the amino acid sequence of one corn peptide was determined. RESULTS: The optimal conditions for alkaline protease hydrolysis were a pH of 9.5, an enzyme/substrate (E/S) ratio of 8 g per 100 g, a liquid/solid ratio of 25 mL g(-1) and a time of 75 min, while the optimal conditions for flavourzyme hydrolysis were a pH of 7, an E/S ratio of 4.2 g per 100 g and a time of 66 min. After gel filtration chromatography, fraction F2 exhibited the highest antioxidant activities. The amino acid sequence of a purified peptide in fraction F2 was determined as Gly-His-Lys-Pro-Ser (507.2 Da). CONCLUSION: The results indicate that corn gluten meal hydrolysates and/or its isolated peptides are potent antioxidants.

[Effects of shading on dry matter accumulation and nutrient absorption of summer maize].

Taking summer maize cultivars Zhenjie 2 (ZJ2), Denghai 605 (DH605), and Zhengdan 958 (ZD958) as test materials, a field trial was conducted to study the effects of shading on the dry matter accumulation and nitrogen (N), phosphorus (P) and potassium (K) absorption of summer maize. Four treatments were installed, i. e., shading from flowering stage to maturity stage (S1), shading from six-leaf stage to flowering stage (S2), shading all through the growth season (S3), and no shading (CK). After shading, the grain yield and dry matter accumulation decreased significantly, and the decrement was related to shading period, showing S3 > S1 > S2. The grain yield in treatments S1, S2, and S3 was averagely 61.6%, 25.3%, and 92.8% lower than that of CK, respectively, indicating that the effects of shading after flowering were greater than those of shading before flowering. The responses of different cultivars to shading presented a similar trend. The nutrient absorption of summer maize before flowering stage showed K > N > P, and the nutrient absorption amount of whole plant showed N>K>P. After shading, the N and P absorption decreased significantly. The plant relative N and P absorption in different treatments had somewhat increase, because the decrement of dry matter accumulation after shading was larger than that of N and P absorption, as compared with the control. After shading, the plant K absorption decreased significantly, and the decrement in S2 was larger than that of dry matter accumulation. Shading before flowering stage had larger effects on the plant K absorption than on the N and P absorption.

[Effects of nitrogen application period on the nitrogen metabolism key enzymes activities and antioxidant characteristics of high-yielding summer maize].

Taking the high-yielding summer maize cultivars Denghai 661 (DH661) and Zhengdan 958 (ZD958) as test materials, a field experiment was conducted to study their grain yield, nitrogen use efficiency, key enzymes activities of nitrogen metabolism, and antioxidant enzymes activities under effects of different nitrogen application periods. One-dose nitrogen application at jointing stage was not beneficial to the increase of grain yield and the nitrogen accumulation in plant and grain, while split application in combination with application after anthesis increased the nitrogen accumulation in plant and grain significantly and increased the grain yield. When the nitrogen was applied at a ratio of 2:4:4 at jointing stage, 10-leaf stage, and 10 days after anthesis, the grain yield of DH661 was up to 14123.0 kg x hm(-2); when the nitrogen was applied at a ratio of 1:2:5:2 as the basal and at jointing stage, 10-leaf stage, and 10 days after anthesis, the grain yield of ZD958 was up to 14517.1 kg x hm(-2). These two nitrogen application modes increased the grain yield of DH661 and ZD958 by 14.5% and 17.5%, respectively, as compared with one-dose nitrogen application at jointing stage. Split nitrogen application before anthesis increased plant nitrate reductase activity significantly. In the 0-42 days after anthesis under split nitrogen application, the glutamine synthetase, glutamate synthase, and glutamate dehydrogenase activities of DH661 and ZD958 were averagely increased by 32.6%, 47.1% and 50.4%, and 14.5%, 61.8% and 25.6%, and the superoxide dismutase and catalase activities were increased by 22. 0% and 36.6%, and 13.4% and 62.0%, respectively, and the malondialdehyde content was decreased significantly, as compared with one-off nitrogen application. It was suggested that for the high-yielding of summer maize, split application of nitrogen and appropriately increasing the nitrogen application ratio after anthesis could enhance the plant key nitrogen metabolism enzymes activities, delay leaf senescence, promote plant nitrogen uptake and its utilization, and increase grain yield.

[Effects of partial root excision on the growth, photosynthesis, and antioxidant enzyme activities of maize under salt stress].

A pot experiment was conducted to study the effects of partial root excision on the growth of two maize cultivars (Zhengdan 958 and Denghai 9) throughout their growth period and the photosynthesis and leaf antioxidant enzyme activities at grain-filling stage under salt stress. Four treatments were installed, i. e., control (no salt), low salt (0.2% NaCl), moderate salt (0.4% NaCl), and high salt (0.6% NaCl). Under low salt stress, the grain yield of Zhengdan 958 and Denghai 9 with partial root excision was increased by 13.1% and 31.4%, respectively, as compared with that of the cultivars with no root excision. At jointing stage, the growth of the cultivars with partial root excision was restrained, the root- and shoot dry masses under the same salt stresses being lesser than those of the cultivars with no root excision, but the growth under the conditions of no salt and low salt recovered quickly. At milk-ripe stage and under no salt and low salt conditions, the root- and shoot dry masses, leaf area, total root length, total root surface area, root activity, leaf chlorophyll content, and ear leaf net photosynthetic rate, stomatal conductance, transpiration rate, and CAT and POD activities of the cultivars with partial root excision were significantly larger than those of the cultivars with no root excision, while the shoot diameter and ear leaf MDA content were in adverse. Moderate and high salt stresses had greater effects on the cultivars with partial root excision. The root- and shoot dry masses, root morphology, and photosynthesis indices of the cultivars with partial root excision were smaller than those of the cultivars with no root excision, so did the grain yields. Throughout the growth period of the cultivars, the growth of the cultivars with partial root excision depended on the salt concentration, i. e., was promoted under no and low salt, and inhibited under moderate and high salt conditions.

[Present situation of maize straw resource utilization and its effect in main maize production regions of China].

A survey was carried out in three main maize production regions in Northeast, North, and Southwest China, including 720 villages of 125 counties, with the purpose of investigating the present situation of maize straw resource utilization and its effect. Among the present utilization ways of maize straw resource, the main ones were returning to soil, feeding livestock, and using as fuel, their proportions being 30.8%, 26.2%, and 24.6%, respectively. In Northeast China, the top three utilization ways were fuel, livestock feed, and returning to soil, with the proportions being 35.4%, 30.8% and 19.8%; in North China, the top three were returning to soil, livestock feed, and fuel, with the proportions being 43.6%, 19.9%, and 17.9%; and in Southwest China, they were returning to soil, livestock feed, and fuel, with the proportions being 29.0%, 27.9%, and 20.5%, respectively. In the survey areas, the proportion of using maize straw as fuel was smaller (12.8%), and that of using as industrial raw material was only 0.7%. Returning maize straw to soil increased maize yield (the increment in Northeast, North, and Southwest China was 632.0, 371.6, and 290.4 kg x hm(-2), respectively), improved soil condition, and decreased the application rates of manure, nitrogen, phosphorus, and potassium fertilizers by 20% -30%, 16%-30%, 24%-34%, and 33%-38%, respectively. The maize yield increased with increasing straw mass and its returning amount and proportion. However, because of wanting complete sets of available machines, straw returning was low in quality, which increased the difficulty in weed controlling and promoted the occurrence of some diseases and insect pests, giving impacts on maize seedlings growth. It would be necessary to strengthen the researches on the related complete set maize straw returning techniques.