Phosphorus nutrition and water stress tolerance in wheat plants

The effect of phosphorus (P) nutrition and soil water availability (W) on the growth of wheat (Triticum aestivum L.) plants was studied in two pot experiments. Several levels of P supply were applied once before sowing. Before seedling establishment, the pots were kept near 100% of field capacity (FC). Afterwards, half of the pots were maintained between 60–70% FC. Control pots were kept at 85–95% FC by weighing and watering every two to three days. Several harvest of shoots were done before anthesis. At each harvest, dry matter and total P accumulation were measured in shoots. The main differences between both experiments were the way the drought stress was imposed, the levels of P supply, and the developmental stage of the plants at each harvest. In Experiment 1, no additional P resulted in a reduction of the shoot dry matter of 24 and 48% for well watered and drought‐stressed plants, respectively. In Experiment 2, these reductions were of 33 and 65% for well‐watered and drought‐stressed plants, respectively. In both experiments, the effect of the drought‐stress treatment was different at different levels of P supply. Interactions between P and W treatments were attributed to both, a less intense drought stress in P0 plants, and to the enhancement of drought‐stress tolerance in P100 plants (Experiment 1), and P60 plants (Experiment 2).     

Effect of seed phosphorus and soil phosphorus applications on early growth of rice (Oryza sativa L.) cv. IR66

Abstract

The vigour and size of rice seedlings in the nursery are generally correlated with final grain yield. The present study examined the possibility that increasing seed phosphorus (P) concentration would stimulate early growth of rice seedlings and therefore would have the potential to increase rice yield. Rice seeds with a uniform size and three levels of P concentration (0.115, 0.173, and 0.240% on a dry weight basis) were sown in pots on a P deficient soil with three levels of P supply (0, 7.75, and 38.8 mg P kg^?1 soil) to investigate their effect on root and shoot dry weight and P accumulation at three harvest times, 10, 20, and 30 d after sowing (DAS). The effect of seed P concentration on plant growth was greatest at a low soil P concentration and it was less pronounced with increasing soil P concentration and with time at all levels of soil P. At 10 DAS, shoot dry weight was 15% higher at a high seed P concentration (0.240%) (p < O.O1) than at a low seed P concentration (0.115%) at each level of soil P supply whereas at subsequent harvests (20 and 30 DAS) the effect of seed P concentration was observed only when the soil P supply was deficient. In contrast with its effects on shoot dry weight, high seed P concentration increased root dry weight only at the latest harvest (30 DAS). The fact that high seed P increased P concentrations in shoot tips, and in roots at 10 DAS suggests that improved P nutrition of seedlings in the first 10 DAS may be the mechanism by which high seed P concentration stimulates early growth, especially in soils with low P concentration. Sowing rice seed with high P concentration may be beneficial for increasing farmer's rice yields, in P deficient soil, and requires further field investigations.     

Influence of phosphorus supply pattern in soil on yield of spring wheat

The purpose of this research was 1) testing the influence of various patterns of supplying phosphorus (P) on dry matter production and biomass allocation in various organs of spring wheat and 2) exploring the optimal P application pattern for high grain yields of spring wheat. Plants were grown in pots constructed with PVC tube, 130 cm long and 10 cm in diameter. Each tube consisted of two segments of 0–43 cm and 43–130 cm. Two soil water regimes were imposed: i) D, water content in the upper soil layer was kept at 50% of field capacity (FC), lower layer (43–130 cm) was at 75–80% of FC and ii) W, a well‐watered control with the entire soil profile being maintained at 75–80 FC. Three P applications were made: i) Pu, P was supplied in the upper 0–43 cm soil layer, ii) Pl, P was supplied in the 43–130 cm layer, and iii) Pe, P was supplied to the entire soil profile. Total photosynthates of plants in WPe and WPu in a whole day were higher than that in DPe and DPu. The photosynthetic rates were similar between WP1 and DPl. The highest P/T (Photosynthesis/ Transpiration) in topsoil drying treatments occurred in DPu, but in wet treatments it was Wpe. The DPu and WPu had similar leaf area, which were significantly higher than other treatments. In the period from the beginning of water treatments to harvest, water consumption in DPe, DPu, DPl, WPe, WPu, and WP1 was 419, 354, 476, 763, 565, 806 mL, respectively. At harvest time, supplied water use efficiencies of DPu and WPu were similar, and reached a peak in both drying and wet treatments. Grain weights per shoot in DPu and WPu were significantly higher than those of other treatments. This implies that phosphorus supplied to the upper soil is beneficial to yield maximum.     

年际间周年覆盖保水对旱地小麦植株氮素利用的调控研究

为深入探索旱地小麦覆盖保水、增产、高效栽培技术途径,于2011—2014年在山西农业大学闻喜试验基地,以夏季覆盖渗水地膜与不覆盖为主区,以生育期膜际条播、常规条播为副区,研究年际间周年覆盖对麦田土壤水分运行和植株氮素积累、利用及氮效率的影响。结果表明:夏季覆盖提高播前3m内土壤水分,其保水效果可至孕穗期,且采用膜际条播效果更佳。夏季覆盖提高各生育时期植株氮素积累量,丰水年效果显著,提高27~31kg/hm~2,且采用膜际条播,夏季覆盖条件下欠水年提升空间较大,提高2~8kg/hm~2。夏季覆盖促进丰水年花前叶片和穗中氮素运转,促进平水年和欠水年茎秆+茎鞘中氮素运转,提高花前氮素运转量及对籽粒的贡献率,尤其欠水年;且采用膜际条播促进平水年茎秆+茎鞘和欠水年叶片中氮素运转,提高花后氮素积累量及对籽粒的贡献率。夏季覆盖提高氮素利用效率和氮素生产效率,欠水年采用膜际条播氮素吸收效率效果更佳;且采用膜际条播提高氮素吸收效率,欠水年夏季覆盖条件下氮素生产效率影响较大。结果还表明,夏季覆盖后,丰水年和平水年单位花后氮素积累量的增产效果较好,每增加1kg/hm~2可增产176~224kg/hm~2,而欠水年单位花前氮素运转量的增产效果较好,每增加1kg/hm~2可增产142~185kg/hm~2;采用膜际条播较常规条播,丰水年和平水年单位花前氮素运转、单位花后氮素积累的增产量均较大,欠水年夏季覆盖条件下采用膜际条播单位花后氮素积累量的增产量较大,每增加1kg/hm~2可增产234kg/hm~2。总之,周年覆盖有利于植株氮素吸收、运转,实现旱地小麦高产高效。     

灌水量和时期对高产小麦氮素积累、分配和转运及土壤硝态氮含量的影响

在每公顷产9000 kg小麦的高产条件下,以济麦22为试验材料,设置全生育期不灌水（W0）、底墒水（W1）、底墒水+拔节水（W2）、底墒水+拔节水+开花水(W3)、底墒水+开花水 (W4) 5个灌溉处理,每次灌水60 mm,研究了灌水量和时期对高产小麦氮素积累、分配和转运及土壤硝态氮含量的影响。结果表明:1）与不灌水处理（W0）相比较,灌水处理显著增加了小麦植株氮素积累量、子粒氮素积累量和开花后营养器官氮素向子粒的转移量;随着灌水量的增加,成熟期小麦植株氮素积累量、开花后营养器官积累的氮素向小麦子粒转移量和转移率均呈现先增加后降低的趋势,以W2处理最高。2）随着小麦生育进程的推进,0—200 cm土层土壤硝态氮含量先降低后回升再降低,在拔节期最低。成熟期,W0处理0—40 cm土层的土壤硝态氮含量显著高于灌水处理;随灌水量的增加,100—160 cm土层土壤硝态氮含量增加,W2处理显著低于W3和W4处理;160—200 cm土层的土壤硝态氮含量无显著差异。3）随灌水量的增加,氮素吸收效率、氮素收获指数和氮肥生产效率先增加后降低,W2处理最高;而氮素利用效率则呈逐渐降低趋势,其中W0处理的氮素利用效率显著高于其他处理,W2、W3、W4处理间无显著差异。在本试验条件下,综合考虑氮素利用、子粒产量和土壤中硝态氮的淋溶,底墒水和拔节水各灌60 mm的W2为最佳处理,可供生产中参考。     

Dry‐matter production,mineral nutrient concentrations,and nutrient distribution and redistribution in irrigated spring wheat

A field study was made of the seasonal changes in dry‐matter production, and the uptake, distribution, and redistribution of 12 mineral nutrients in the semi‐dwarf spring wheat, Egret, grown under typical irrigation farming conditions. Most of the dry‐matter production and nutrient uptake had occurred by anthesis, with 75–100% of the final content of magnesium (Mg), copper (Cu), chloride (Cl), sulfur (S), phosphorus (P), nitrogen (N), and potassium (K) being taken up in the pre‐anthesis period. The above‐ground dry‐matter harvest index was 37%, and grain made up 76% of the head dry matter. Redistributed dry matter from stems and leaves could have provided 29% of the grain dry matter. Concentrations of phloemmobile nutrients, such as N and P, decreased in the leaves and stems throughout the season, whereas concentrations of phloem‐immobile nutrients, such as calcium (Ca) and iron (Fe), generally increased. The decline in the N concentration in stems and leaves was not prevented by N fertilizer applied just before anthesis. Leaves had the major proportion of most nutrients in young plants, but stems had the major proportion of these nutrients at anthesis. Grain had over 70% of the N and P, and 31–64% of the Mg, manganese (Mn), S, and zinc (Zn), but less than 20% of the K, Ca, sodium (Na), Cl, and Fe in the plant. Over 70% of the N and P, and from 15 to 51% of the Mg, K, Cu, S, and Zn was apparently redistributed from stems and leaves to developing grain. There was negligible redistribution of Ca, Na, Cl, Fe, and Mn from vegetative organs. Redistribution from stems and leaves could have provided 100% of the K, 68–72% of the N and P, and 33–48% of the Zn, Cu, Mg, and S accumulated by grain. It was concluded that the distribution patterns of some key nutrients such as N, P, and K have not changed much in the transition from tall to semi‐dwarf wheats, and that the capacity of wheat to redistribute dry matter and nutrients to grain is a valuable trait when nutrient uptake is severely restricted in the post‐anthesis period.     

Differential accumulation patterns of phosphorus and potassium by canola cultivars compared to wheat

The phosphorus (P) and potassium (K) accumulation patterns of canola (Brassica napus L.) are poorly understood, although such information is essential for determining optimal P‐ and K‐fertilizer strategies. This study investigated the patterns of P and K uptake and distribution among plant organs of three early or midmaturing canola cultivars (Tribune, Trigold, and Boomer) differing in K efficiency compared to wheat (Triticum aestivum L. cv. Nyabing). Plants were grown in a glasshouse with nonlimiting P and K supply and harvested at eight growth stages until maturity. Maximum P accumulation by all canola cultivars occurred during late flowering (GS 5,5; 84 d after sowing), whereas P accumulation in wheat plants peaked just prior to anthesis (Z59; 73 d after sowing). Maximum accumulation of K in canola cultivars Tribune and Trigold occurred 73 d after sowing (GS 4,8), but peaked earlier (61 d after sowing) in Boomer canola (GS 4,2) and Nyabing wheat (Z55). The results highlight the importance of early P and K supply to both species; however, the extended uptake of P and K by the canola cultivars Trigold and Tribune compared to wheat suggests that availability of soil P or K postflowering may be of more importance to canola than to wheat.     

Partitioning of phosphorus in different height isolines of winter wheat

Wheat (Triticum aestivum L.) grain yields and composition are influenced greatly by P and its interactions with other nutrients. Because most P in grain, like N, is remobilized from vegetative parts, high harvest index of dwarf wheats may adversely influence partitioning of P to grain. Isogenic tall, single semidwarf, and double dwarf ‘Pawnee’ wheat lines were used to characterize P partitioning, P nutrition before and after anthesis, and relationship between P and N. Plants were grown in hydroponic cultures with three P levels; the first study determined P, N, and dry matter accumulation from anthesis to maturity, the second study determined the effect of withholding P after anthesis on P, N, and dry matter partitioning during grain development. Plants continued to absorb P when it was available after anthesis, but grain growth was influenced more by P nutrition before anthesis than after anthesis. Leaf blades, sheaths, and stems were major sources of P for grain growth when the nutrient was withheld and major sites of P accumulation when the nutrient was supplied after anthesis. Content of N in plants was favored by ample P levels. Dwarfing genes increased harvest index, but had little effect on P partitioning because of differences in dry matter accumulation.     

Effects of early mycorrhization and colonized root length on low‐soil‐phosphorus resistance of West African pearl millet

Phosphorus (P) deficiency at early seedling stages is a critical determinant for survival and final yield of pearl millet in multi‐stress Sahelian environments. Longer roots and colonization with arbuscular mycorrhizal fungi (AMF) enhance P uptake and crop performance of millet. Assessing the genotypic variation of early mycorrhization and its effect on plant growth is necessary to better understand mechanisms of resistance to low soil P and to use them in breeding strategies for low P. Therefore, in this study, eight pearl millet varieties contrasting in low‐P resistance were grown in pots under low P (no additional P supply) and high P (+ 0.4 g P pot^?1) conditions, and harvested 2, 4, 6, and 8 weeks after sowing (WAS). Root length was calculated 2 WAS by scanning of dissected roots and evaluation with WinRhizo software. AM infection (%) and P uptake (shoot P concentration multiplied per shoot dry matter) were measured at each harvest. Across harvests under low P (3.3 mg Bray P kg^?1), resistant genotypes had greater total root length infected with AMF (837 m), higher percentage of AMF colonization (11.6%), and increased P uptake (69.4 mg P plant^?1) than sensitive genotypes (177 m, 7.1% colonization and 46.4 mg P plant^?1, respectively). Two WAS, resistant genotypes were infected almost twice as much as sensitive ones (4.1% and 2.1%) and the individual resistant genotypes differed in the percentage of AMF infection. AMF colonization was positively related to final dry matter production in pots, which corresponded to field performance. Early mycorrhization enhanced P uptake in pearl millet grown under P‐deficient conditions, with the genotypic variation for this parameter allowing selection for better performance under field conditions.     

Response of Sauropus androgynus to soil phosphorus concentration and mycorrhizal colonization

Thirty three‐day‐old seedlings of nonmycorrhizal Sauropus androgynus were transplanted into pots containing a subsurface Oxisol uninoculated or inoculated with Glomus aggregation at three target soil solution phosphorus (P) concentrations. While no evidence of vesicular‐arbuscular mycorrhizal fungal (VAMF) colonization was noticed in the uninoculated soil, sauropus roots were colonized to the extent of 54%, 60% and 38% in the inoculated soil if target soil P concentrations were 0.014, 0.02 and 0.2 mg/L. VAMF colonization led to significant increases in tissue P and shoot dry matter accumulation at the first two soil P concentrations but not at the highest concentration. Root dry matter yield of mycorrhizal sauropus was greater than that of nonmycorrhizal sauropus at all soil P concentrations tested. Although mycorrhizal inoculation effects at soil P concentrations of 0.014 and 0.02 mg/L were comparable, growth of mycorrhizal plants was greater at the latter P concentration than at the former. Growth of mycorrhizal sauropus at this P concentration was also comparable to non‐mycorrhizal growth of the plant at soil P concentration of 0.2 mg/L. Based on the growth responses observed sauropus was classified as a highly mycorrhizal dependent species.     

Soil phosphorus testing for intensive vegetable cropping

Environmental concerns and rapidly decreasing phosphorus (P) resources caused a renewed interest in improving soil P tests for a more efficient P fertilization. This led to the development of better P fertilizer recommendation systems for major arable crops and grass. Nevertheless, these P fertilizer recommendation systems seem to fail for intensive vegetable crops, with often a very short growing season and limited rooting system. This leads to low P use efficiencies in the horticultural sector. In order to address this problem we set up a study to answer following questions: (1) which soil P test predicts the plant available P content for intensive vegetable crops the best and (2) can new insights, such as combining different soil P tests, improve P fertilizer recommendations for intensive vegetable crops? To this end, bulk samples of 41 soils with very different P status (based on ammonium lactate extractable P) were collected. The plant available P content of these soils was determined using six commonly used soil P tests (P‐CaCl₂, P‐water, P‐Olsen, P‐acetate, P‐lactate, and P‐oxalate) and a P fertilizer pot experiment with endive (a very P sensitive vegetable crop) was conducted. Six pots of each soil were planted with endive. Three of these pots received no P fertilization (0P) and three pots received ammonium polyphosphate equivalent to 24 kg P ha^?1 (24P). All other factors were kept constant. Relative crop yield of the 0P fertilized plants compared to the 24P fertilized plants was determined. Plotting these relative yields against the P status of the soil per soil P test allowed to fit a Mitscherlich curve through the data. Also the combination of two different soil P tests to predict the relative yield with a Mitscherlich equation was evaluated. The coefficients of variation of the soil P tests, the R² values and the relative standard errors of the parameter estimates revealed that P‐acetate and P‐water predicted the relative yield of the 0P plants the best and that combining two different soil P tests gave no extra predictive power. This finding may form the basis for the development of a new P fertilizer recommendation system for intensive vegetable crops, leading to an improved P use efficiency in horticulture. In order to develop this new system more data relating soil P test values with RY of intensive vegetable crops should be collected.     

磷肥对日光温室番茄磷营养和产量及土壤酶活性的影响

采用盆栽方法进行了不同施磷（P2O5）水平下,日光温室番茄产量、不同生育期番茄磷素分配、干物质积累、土壤速效磷含量和酶活性研究,并确定了适宜番茄生长的最佳施磷量与土壤速效磷含量。结果表明,随着磷肥施用量的增加,土壤速效磷含量及番茄各组织含磷量相应增加;当施用P2O5达到0.53 g/kg（处理5）,土壤速效磷含量在60～77 mg/kg时,较适宜番茄生长,番茄产量和单果重达最高,根系和茎叶干物质积累也达到最好水平。当施磷量超过0.53 g/kg时,造成土壤和植株磷累积过高,易引起土壤盐害,降低土壤酶活性,从而降低干物质积累和番茄产量,影响土壤的可持续利用。     

减施磷肥提高设施番茄氮磷钾生理效率并减少土壤速效磷累积

【目的】设施蔬菜生产中过量施肥现象普遍存在,本研究针对设施番茄磷肥过量施用问题,定位研究减施磷肥对番茄产量、干物质量、养分吸收、分配及土壤速效磷状况的影响,旨在为设施栽培磷肥减量提供科学依据。【方法】以习惯施肥为对照 (CK),2015年设磷肥减量50% (P1)、磷肥减量70% (P2) 2个减磷处理,2016年增设不施磷 (P0) 处理,共3个减磷处理。2016年在膨果期、盛果期采集植株样品,测定根、茎、叶、果干重,及各器官氮、磷、钾养分含量;在定植前、盛果期和拉秧期采集0—60 cm土层土壤样品,测定土壤速效磷含量。【结果】在基础速效磷含量较高 (约220 mg/kg) 的土壤,连续两年减磷70%或一年不施磷肥不影响番茄产量,2015年和2016年番茄产量分别为53.9～55.1 t/hm2和50.2～52.7 t/hm2。各减磷施肥处理与CK相比,均显著提高盛果期果实干物质量和N、P、K养分分配率,降低叶片干物质量、干物质分配率和N、P、K养分分配率。膨果期番茄植株62.8%～65.7%干物质分配于叶片,植株氮、磷、钾携出量分别为83.2～89.9 kg/hm2、10.3～11.1 kg/hm2、75.0～85.9 kg/hm2,此时番茄叶片和茎杆是养分的主要累积部位,茎叶氮、磷、钾分配率之和分别为84.4%～86.4%、79.4%～83.4%、76.9%～82.3%,番茄氮、磷、钾吸收比例为1∶0.12∶0.84～0.96。盛果期43.0%～44.6%和37.0%～44.6%的干物质分配于果实和叶片,此时番茄果实和叶片为养分主要累积部位,果实和叶片氮、磷、钾分配率之和分别为84.6%～86.7%、78.5%～82.7%、81.4%～83.9%,植株氮、磷、钾携出量分别为197～226 kg/hm2、33～37 kg/hm2、200～247 kg/hm2。CK处理番茄叶片、果实全钾含量及钾吸收量显著高于减磷处理,可见减施磷肥可降低番茄对钾素的奢侈吸收。经过两年的减磷处理,表层土壤速效磷累积量显著降低,但各处理土壤剖面出现磷素向下迁移,膨果期0—20 cm土层土壤速效磷含量较种植前减少27.0～60.9 mg/kg,20—60 cm土壤速效磷增量在11.8～50.1 mg/kg,减磷处理显著降低20—60 cm土壤速效磷增加量。【结论】在基础磷素含量较高的土壤上,较农民习惯施磷连续两年减少70%的磷肥用量没有影响番茄产量,降低番茄对钾素的奢侈吸收,减缓土壤速效磷累积。两年连续减施磷肥的土壤速效磷含量仍处于较高水平,可见该研究区域设施蔬菜生产减磷潜力仍较大。     

IAA and 4‐Cl‐IAA Increases the Growth and Nitrogen Fixation in Mung Bean

A commonly occurring auxin indole‐3‐aceticacid (IAA) and a rarely occurring chlorosubstituted auxin (4‐Cl‐IAA) were compared for their impact on growth and nitrogen metabolism in mung bean for the first time. The plants were generated from healthy and Rhizobium coated seeds in earthen pots. The seedlings at 7 and/or 14 days were percolated with 0, 10^?10, 10^?8, or 10^?6 M of IAA or 4‐Cl‐IAA. The plants were sampled at 30 days after sowing (DAS) to assess the growth and various biochemical characteristics. The auxins significantly enhanced the growth (length and dry mass of shoot and root), nodule fresh mass, nitrogenase activity in fresh nodules, leaf carbonic anhydrase activity, chlorophyll content, and rate of photosynthesis. The effect of the auxins lasted up to the harvest where the seed yield, 100 seed mass, and number of pods per plant were significantly affected by the auxins. At a moderate concentration (10^?8 M), 4‐Cl‐IAA generated the best response. However, a comparable response was generated by the higher concentration (10^?6 M) of 4‐Cl‐IAA. The application of the hormone twice (at 7 and 14 DAS) was much more effective than single application (at 7 or 14 DAS). It was concluded that IAA and 4‐Cl‐IAA improved the growth and nitrogen fixation in mung bean. The 4‐Cl‐IAA proved more effective than IAA.     

Organ-specific allocation pattern of acquired phosphorus and dry matter in two rice genotypes with contrasting tolerance to phosphorus deficiency

ABSTRACT

Our earlier study demonstrated that the landrace of Japonica rice, Akamai exhibits low-P (phosphorous) tolerance mechanisms compared to the conventional type cultivar, Koshihikari. The present study examined the genotypic difference of yield, plasticity of root growth, and internal utilization of acquired P (allocation pattern of biomass and P among different vegetative and reproductive organs) of two contrasting cultivars in response to P-deficiency. Each cultivar was grown until maturity with (+P) and without (–P) P supply in pots (two plants per pot) filled with 15 kg of Regosol soil. Grain yield and yield components were determined along with biomass and P accumulation in different vegetative and reproductive organs. To assess the plasticity of root growth, the soil column in the pot was divided into two equal portions (upper and lower soil layers) in which the root dry weight and length were measured separately. Among the investigated yield components, the number of filled grains per panicle was the key parameter determining genotypic differences of grain yield of two cultivars. P-deficiency had a marked influence on grain filling of Koshihikari where the filled grain percentage under –P condition was reduced by 29% compared to that under +P condition. However, the respective reduction for Akamai was only 11%. Low-P tolerance ability of Akamai imparts a yield advantage over Koshihikari under P-deficient conditions because of the production of the higher number of filled grains per panicle. Akamai explored both upper and lower soil layers of the pot more efficiently in search of P through greater root biomass and length. Akamai grown under P-deficient conditions had remarkably lower P concentrations in less active vegetative tissues (partly and fully senesced leaves) than those of Koshihikari; whereas, more active organs (green leaves and panicles) contained a greater amount of P. Akamai’s higher plasticity to external P availability can be a genetic resource for developing low-P tolerant, high-yielding rice genotypes suitable for predicted future P-limited environments.     

Mobilization of phosphorus contributes to positive rotational effects of leguminous cover crops on maize grown on soils from northern Nigeria

Previous research has demonstrated a positive rotational effect of tropical leguminous cover crops on maize growth on a luvisol from Nigeria. This effect could not be explained by a better N supply. The objective of the present work was to further clarify whether improved P nutrition has been a contributing factor. Nine cover crops and maize were studied in nutrient solution‐culture with 1 and 20 μM P and with NO₃‐N as N source for root physiological parameters that may affect P mobilization. Zea mays, Lablab purpureus, and Centrosema pubescens responded to P deficiency by higher rates of proton excretion. Clitoria ternatea excreted OH^— with only small differences due to P nutrition. At low P supply, Chamaecrista rotundifolia, Clitoria, and Centrosema had the highest exudation rates of organic acid anions, especially citrate and malate. A major difference between plant species was found in root‐surface acid phosphatase activity. Cajanus cajan expressed the highest phosphatase activity. V_max of P uptake increased markedly under P deficiency, particularly for maize. Compared to the other plant species Cajanus, Chamaecrista, and Clitoria were characterized by a greater capability to absorb P at low external P concentrations. The nine cover crops and maize were also grown in pot experiments using two soils from northern Nigeria low in available P. The ultisol from Jos had a high P fixation capacity and was more acidic than the alfisol from Zaria. All plant species were precultured in the first season at 100 (Zaria) and 250 (Jos) mg P per pot. In the subsequent season, maize was uniformly seeded into all pots containing the remaining roots and the incorporated shoot dry mass (according to 15 mg P per pot) of the pre‐crop. No P and 250 (Zaria) or 500 (Jos) mg P per pot were freshly applied. Maize growth and P uptake were enhanced after legumes in Zaria soil. Cajanus showed the highest residual effect, and also Clitoria, Chamaecrista, and Lablab showed effects superior to the mean. In Jos soil, Clitoria, Cajanus, and Lablab enhanced maize growth above average. Also, a highly significant positive correlation between P uptake and biomass production was obtained. These results indicate that enhancement of maize growth after leguminous cover crops, at the low P supply of the soil used, mainly depends on P mobilization capacity of the cover crop.     

The electro-ultrafiltration method for controlling the effect of Bacillus cereus on phosphorus mobilization in a calcareous soil

Summary The effects of phosphate-solubilizing bacteria on the phosphorus mobilization and P utake by Lolium multiflorum from a calcareous soil were investigated using a greenhouse pot experiment. The soil was inoculated with Bacillus cereus and the pots were either planted with Lolium multiflorum or left fallow. Treatments were designed to study the effect of inoculation of phosphate-solubilizing bacteria on phosphorus dynamics throughout the experiment. The dynamics were studied by the electro-ultrafiltration method, the results of which were used to interpret phosphorus mobilization in the soil. Phosphate uptake by L. multiflorum from the inoculated soil showed a 40% increase over the control soil, and an increase in total dry matter of 50%.     

不同播期冬小麦小花发育特性与同化物代谢的相关性

【目的】推迟播期能够维持单位面积粒数已在前期研究中得到证实,本研究进一步探讨不同播种期冬小麦小花发育特征及分化、退化的差异性,分析植株同化物积累、分配与小花发育和结实的关系,旨在为提高小麦穗粒数以及丰富小麦高产栽培理论提供参考。【方法】试验于2014—2015年和2015—2016年连续两个小麦生长季,在山东省泰安市岱岳区大汶口镇东武村山东农业大学试验田 (35°57′N,117°3′E) 进行,以泰农18和济麦22为试验材料,设置9月24日、10月1日、10月8日、10月15日和10月22日共5个播期处理,观察记载小花发育过程中分化和退化数量动态以及最终结实粒数,测定开花期穗部和茎秆的干物质和氮素积累量,计算小花退化阶段整株和穗部的干物质和氮素积累速率。【结果】播期推迟条件下,单位面积可孕花数和单位面积结实粒数获得了维持,单位面积最大分化小花数明显降低,小花存活率显著提高。推迟播期明显减少了小花退化数量,小花退化速率明显降低。在小花退化阶段,推迟播期加速了整株和穗部的干物质和氮素积累,从而为开花期穗干重的维持以及干重穗茎比和氮素穗茎比的提高提供了保证。相关分析表明,开花期单位面积可孕花数分别与穗干物重、干物重和氮积累量穗茎比、整株和穗的干物质和氮的积累速率以及小花存活率均呈极显著正相关。推迟播期明显减少了有效茎蘖和无效分蘖所产生的退化小花数,尤其无效分蘖产生的退化小花数下降幅度更加明显。提高主茎在群体中同化物所占比例能够有效维持单位面积可孕花数和减少退化小花数,降低了小花死亡消耗。此外,推迟播期提高了可孕花累积生长度日生产效率,降低了退化小花累积生长度日生产效率。【结论】推迟播期明显降低了小花的退化,从而提高了小花存活率,开花期单位面积可孕花数的维持与植株同化物代谢密切相关。适期晚播提高了主茎在群体中的比重,有利于减少无效消耗和提高资源利用效率。     

密度对沿淮晚播小麦产量形成及品质性状的影响

目前晚播小麦的面积不断增加,为明确沿淮地区晚播小麦的适宜种植密度,采用裂区试验设计,于2013—2015年在不同晚播条件下(11月5日、11月15日、11月25日),设置3个种植密度(300万株·hm-2、450万株·hm-2、600万株·hm-2),分析种植密度对玉米茬晚播小麦产量形成及品质性状的影响。结果表明:播期推迟导致小麦生育期滞后,主要影响拔节期前营养生长期的长短;密度对生育进程无显著影响。随播期推迟,小麦开花期和成熟期的干物质积累量下降,花前贮存同化物的转运量和花后同化物的积累量下降,花后同化物对籽粒贡献率明显增加;穗数、穗粒数和千粒重均有所下降,进而产量显著下降;蛋白质含量、湿面筋含量和沉淀值上升。播期对分蘖穗干物质积累与运转及产量构成因素的影响均大于主茎穗。与11月5日播期相比,11月25日播期下开花期干物质积累量、成熟期营养器官积累量、籽粒干重、花前营养器官贮存同化物的转运量及其对籽粒的贡献率在主茎穗中分别下降13.37%、9.96%、9.04%、25.37%和17.07%,在分蘖穗中分别下降55.71%、54.34%、51.80%、59.70%和22.70%。同一播期条件下,随着种植密度的增加,小麦开花期和成熟期的干物质积累量上升,花前贮存同化物的转运量减少,花后同化物的积累量及其对籽粒贡献率增加;穗数增加,千粒重降低;蛋白质含量和湿面筋含量上升,沉淀值下降。与主茎穗相比,密度对分蘖穗干物质积累与运转及产量构成因素的影响更大。与300万株·hm-2密度相比,600万株·hm-2密度下单穗粒重、穗粒数和千粒重在主茎穗中分别下降17.90%、13.60%和4.76%,在分蘖穗中分别下降20.17%、14.46%和6.23%。可见,适当增加密度有利于增加晚播小麦产量并改善晚播小麦品质性状,本研究中11月15日、11月25日两晚播条件下适宜密度分别为450万株·hm-2、600万株·hm-2。     

底墒和磷肥对渭北旱塬冬小麦产量与水肥利用的影响

在陕西杨凌渭北旱塬进行5年定位试验,在施N160kg/hm2的基础上,设施P2O5 0、50、100、150 kg/hm2 4个施磷水平,结合5年降水情况,分析了播前底墒、施磷对旱地冬小麦产量及水肥利用的影响。结果表明,夏季7～9月的降水是决定渭北旱塬小麦播前底墒的关键因素,两者呈线性相关夏季每增加1 mm降水,土壤贮水增加0.5mm。要保持这一地区小麦稳产或高产,底墒应保持550 mm左右,夏季降水应有380 mm左右。夏季降水充足的年份,施磷量增加造成的下季小麦播前底墒下降不明显;降水偏少的（350mm）的年份,合理施磷能够促进小麦生长,导致生育期内对土壤水分消耗较多,降低土壤含水量,使前季小麦每增施磷50 kg/hm2,下季小麦播前底墒减少9～12 mm。除底墒外,关键生育期的充足降水也是保证旱地小麦产量重要因素,每毫米播前底墒能形成9.0～9.9 kg/hm2、生育期降水形成28.6～33.3 kg/hm2小麦子粒产量。施磷水平决定了作物生物量、产量高低;底墒决定了水分和磷肥利用的程度或水平,同时水分也制约着作物累积的干物质向收获器官（子粒）转移的多少或比例。在底墒充足的年份,较低的施磷量,就可实现较高的产量和水肥利用效率;底墒较差的年份,则要求较高的磷肥投入量。