Middle Growth Stages Research Articles

Effects of fractionated nitrogen application on leaf senescence and <SUP>15</SUP> N-urea uptake and utilization of apple rootstock―<I>Malus hupenhensis</I>

Aims The effects of fractionated nitrogen (N) fertilization (once, twice and thrice) on leaf senescence and nitro- gen uptake and utilization of potted Malus hupenhensis were explored using the 15 N labeling technique. Methods We measured growth parameters such as plant height, stem diameter, leaf area and chlorophyll content (SPAD), enzyme parameters such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in leaves and 15 N parameters such as uptake and utilization for potted M. hupehensis under different fractionated N applications. Important findings Plant height, stem diameter, leaf area and SPAD were highest at early growth stage for once fractionated application and lower for twice fractionated application, and lowest for thrice fractionated applica- tion. At middle growth stage, twice fractionated application showed the highest values, while once fractionated application exhibited the lowest values. At the late growth stage, thrice fractionated application was the highest, while once fractionated application was the lowest. The leaf SOD, POD and CAT activities were highest for once fractionated application at early growth stage and lowest for thrice fractionated application. At the middle growth stage, twice fractionated application was the highest, whereas once fractionated application was lowest. At the late growth stage, thrice fractionated application showed the highest values, while once fractionated application had the lowest values. The 15 N derived from fertilizer (Ndff) value in different organs was significantly different. Thrice fractionated application demonstrated higher values than either of once and twice fractionated application at the late growth stage. Plant total N, 15 N uptake and N-usage efficiency were highest for thrice fractionated application at late growth stage. This indicates that thrice fractionated application not only can enhance the total N content of leaves and delay leaf senescence, but also can increase the N-usage efficiency.

Evapotranspiration models for a maize agro-ecosystem in irrigated and rainfed conditions

A high level of accuracy in the estimation of crop evapotranspiration (ET) may lead to significant savings of economic and water resources in irrigated agriculture. Although ET is a fundamental process in many applications, it cannot be directly measured but it has to be estimated by monitoring the exchange of energy/water above the vegetated surface (micrometeorological methods), or as a residual term of the hydrological balance (lysimeters, soil water budget). The techniques to be adopted are often complex, costly and require specific equipment. Thus, since the ‘50s, many researchers have devoted their activity to the development of models for its estimation. The available approaches can be classified in “direct” methods, based on the original Penman-Monteith (PM) equation, in which the canopy resistance rc is modelled, and “indirect” methods, based on the preliminary calculation of ET for a well-watered reference grass (ET0) with a constant rc, which is then multiplied by a crop coefficient Kc and, in case, by a stress coefficient Ks to obtain ET. Even if the latter approaches are more widely adopted for their practical simplicity, many authors show that the former often provide better ET estimates in absence of calibration of crop parameters. In this study the performances of different direct and indirect methods were evaluated in the case of a surface irrigated and of a rainfed maize grown in the Padana Plain (Northern Italy). The following models were considered: the “one-layer” original PM equation with three different models for rc (Monteith, Jarvis, Katerji-Perrier), the “two-layers” PM model proposed by Shuttleworth and Wallace, the “single” and “double” crop coefficient models illustrated in the Paper FAO-56. Latent heat fluxes measured in 2006 and 2011 in an experimental maize field by eddy-covariance were used to evaluate the models accuracy. Crop, soil and meteo data monitored contextually were used for the implementation of the different models. Results confirm that direct methods are more performing for both irrigated (2006) and rainfed (2011) conditions, with the SW model providing the best results and the FAO-56 models with generalized crop coefficients overestimating ET, especially during the middle growth stage.

沟垄全覆盖种植方式对旱地玉米生长及水分利用效率的影响

2008-2010年在渭北旱塬区,以沟不覆盖为对照(CK),研究垄上覆地膜沟内分别覆普通地膜(PP)、生物降解膜(PB)、玉米秸秆(PS)和液体地膜(PL)4种沟垄全覆盖种植模式对土壤水温、玉米生长、产量及水分利用效率的影响。结果表明,在玉米生长前期,PP、PB和PS处理可明显提高0-200 cm土壤蓄水量;生育中期,PS处理蓄水保墒效果最为显著;生育后期,各沟垄全覆盖处理与对照的土壤蓄水量无显著差异;整个生育期PL处理与CK的土壤蓄水量差异不显著。PP和PB处理3a玉米生育期5-25 cm平均土壤温度分别较CK增高1.6 ℃和1.3 ℃,PS处理降低1.9 ℃,而PL处理与CK无显著差异。PP和PB的增温保水效应使玉米株高、叶面积及地上生物量均高于CK;PS处理的降温效应促进玉米中后期生长,其株高、叶面积及地上生物量均高于CK;PL处理对玉米各生长指标影响不显著。与CK相比,PP、PB和PS处理3a平均的籽粒产量分别提高13.0%、13.8%和15.0%,水分利用效率分别提高9.8%、10.2%和11.6%。可见,垄覆地膜沟覆地膜、生物降解膜或秸秆的沟垄全覆盖种植可明显改善土壤的水温状况,促进玉米生长,从而显著提高作物产量和水分利用效率,对渭北旱塬区春玉米丰产栽培具有重要指导意义。;From 2008-2010, we conducted a field experiment in the Weibei Highlands to determine the effects of planting with ridge and furrow mulching on the soil water and temperature, and the maize growth, yield, and water use efficiency. Ridges were covered with plastic film in all treatments, while furrows were mulched with plastic film (PP), biodegradable film (PB), corn straw (PS), or liquid film (PL). In the control treatment (CK), ridges were covered with standard plastic film, while furrows received no mulching. The three-year trial showed that, during the early maize growth stage, the soil water storage (0-200 cm) was significantly higher with the PP, PB, and PS treatments compared with CK. The three-year average water storage increased by 14.1, 17.9, and 22.2 mm compared with CK. Our analysis of the vertical distribution of the soil water content in the 0-200 cm soil profile showed that the soil water content at the 0-20 cm and 100-200 cm depth were higher with PP, PB, and PS compared with CK. The effect of PS on water conservation was the highest during the middle growth stage, while the three-year average water storage was 16.9 mm higher with the PS treatment than CK. However, the soil storage with PP and PB was significantly lower than CK in 2008 and 2009. Compared with CK, the soil water content with PP and PB increased significantly at the 0-200 cm depth, whereas it decreased at the 80-180 cm depth. There were no significant differences among the mulching treatments during the later growth stage. Soil water storage was slightly higher with PL than CK, while there were no differences in soil water storage between the two treatments during the entire maize growing season. The three-year mean soil temperatures (5-25 cm) with the PP and PB treatments were 1.6 ℃ and 1.3 ℃ higher than CK, respectively, whereas the PS treatment was 1.9 ℃ lower than CK. However, there was no significant difference in the soil temperature with the PL treatment and CK during the maize growing season. The water retention and temperature-raising effects of the PP and PB treatments increased the plant height, leaf area, and aboveground biomass by 2.3% and 2.4%, 30.9% and 29.9%, and 15.5% and 13.9%, compared with CK, respectively, while the maize growing period was reduced by 5-6 d. The cooling effect of the PS treatment also increased the plant height, leaf area, and aboveground biomass by 7.0%, 34.6%, and 6.5% compared with CK, respectively, although the growing period was extended by 4-5 d. There was no difference between the maize growth indices of the PL treatment and CK during the entire maize growing period. PP, PB, and PS produced a higher maize yield and water use efficiency throughout the experimental period. Compared with CK, the PP, PB, and PS treatments increased the three-year mean maize yields by 13.0%, 13.8%, and 15.0%, with water use efficiency improvements of 9.8%, 10.2%, and 11.6%, respectively. Therefore, covering ridges with plastic film and mulching furrows with plastic film, biodegradable film, or corn straw, greatly improved the soil water and temperature status, promoted maize growth, and significantly increased the crop yield and water use efficiency. These results may have important implications for maize production in the Weibei Highlands, China.

Effect of Different Nitrogen Fertilizer Types and Application Measures on Temporal and Spatial Variation of Soil Nitrate-Nitrogen at Cucumber Field

Nitrate-nitrogen content of groundwater are ever-increasing in underneath vegetable growing areas, in this paper, based on field test of cucumber cultivated in Solar Greenhouse in North China, we study the effects of different nitrogen fertilizer application levels (250, 300, 350kg/hm2) and different nitrogen fertilizer types (urea, urea + nitrification inhibitor, slow-release fertilizer) on temporal and spatial variation of soil nitrate-nitrogen content in different soil depth, soil nitrogen fertilizer retention and nitrogen use efficiency during cucumber growth period. The results show that, in the cases of nitrogen fertilizer types (urea and urea + nitrification inhibitor), for surface soil (0 - 40 cm soil depth), the temporal trend of soil nitrate-nitrogen content variation is similar: during the early stage of cucumber growth, soil nitrate-nitrogen content is relatively high; during the middle stage of cucumber growth, as nitrogen is constantly being absorbed by the vegetable, soil nitrate-nitrogen content decrease; during the late stage of cucumber growth, soil nitrate-nitrogen content increase, and increase more significantly when nitrification inhibitor is added in the fertilizer. For deep soil layer (40 - 100 cm depth), when only using urea, the temporal trend of soil nitrate-nitrogen content variation is that of continuous increase, when adding nitrification inhibitor, the temporal trend of soil nitrate-nitrogen content variation is that of insignificant increase. In the case of slow-release fertilizer, for both surface soil and deep soil layer, the temporal trend of soil nitrate-nitrogen content variation is that of continuous decrease. For all three types of nitrogen fertilizer, as fertilization level increase, soil nitrate-nitrogen content in various soil layers increase with it. In the case of fertilization at 300 kg/hm2 and 350 kg/hm2, adding nitrification inhibitor can increase soil retention of nitrogen fertilizer. This study suggests that adding nitrification inhibitors can increase soil retention of nitrogen fertilizer, decrease nitrate-nitrogen leaching downward, thereby reducing the pollution to groundwater.

Effect of Gibberellic acid (GA3) and α-naphthalene acetic acid (NAA) on the growth of unproductive tillers and the grain yield of rice (Oryza sativa L.)

In the present study, GA3 and NAA were used to inhibit the growth of unproductive tillers of rice plants, and we measured the tiller occur and the grain yield of different treatments, the object of this study was to determine the effect of external hormones on the tiller growth and grain yield, and whether we can regulate the tiller growth by some manipulations of the hormone levels. The results indicated that external 10 mg L-1 GA3 and 1000 mg L-1 NAA significantly inhibit the growth of unproductive tillers, and the elimination of unproductive tillers promoted the growth of productive tillers at the middle and late growth stages, and promoted the development of heavy panicles, and finally increased the grain yield. However, the external 100 mg L-1 GA3 (G100) significantly decreased the grain yield of Yangdao 6. The reason was that the most of the plants of G100 treatment of Yangdao 6 were lodging at filling stage, and the lodging significantly decreased the spikelet filling and grain weight, and finally decreased the grain yield. These results suggested that the application of GA3 in field production may lead to lodging, especially for the indica cultivars. So in field production, GA3 should be used carefully. Key words: Rice (Oryza sativa L.), gibberellic acid (GA3), α-naphthalene acetic acid (NAA), tiller, yield.

Dosage Adjustment for Pesticide Application in Vineyards

Traditional pesticide application in grapevines causes large losses to the air and the ground, particularly in early to mid-season applications. Traditional application rates do not differ much according to the season. Canopy size varies as growers choose different row widths, varieties, and trellis designs; however, pesticide labels for vineyard sprays persist in using ground area based application rates. That is why dosage adjustments according to the canopy characteristics have been developed. In the trial described in this article, three adjustment methods, unit canopy row (UCR) (Australia), DOSAVIA (Spain and U.S.), and leaf wall area (LWA) (Germany and Belgium) are compared with traditional American application rates. This article presents the methodology and results of the study. In total, three trials were completed. Results demonstrated that at the early growth stage, deposits with the DOSAVIA and LWA methods were not significantly different from that of the traditional method, and deposits were not different from each other among DOSAVIA, LWA, and UCR (application rates were 327, 281, 234, and 187 L ha-1 for the traditional, LWA, DOSAVIA, and UCR methods, respectively). Concerning the uniformity of distribution, UCR achieved the best results in the early growth stage, followed by LWA. At the middle growth stage, LWA and the traditional method achieved similar results, while deposits using DOSAVIA and UCR were not significantly different. At the middle growth stage, the application rate was increased to 700 L ha-1 for the traditional method and to 560, 327, and 374 L ha-1, respectively, for LWA, DOSAVIA, and UCR. The application rate was increased significantly according to the hugely changed canopy size. The LWA method achieved the best results in terms of deposits and uniformity of distribution. At the late growth stage, the traditional method achieved the highest deposits, while LWA and DOSAVIA achieved similar deposits. The lowest deposits in the canopy occurred with DOSAVIA and UCR. The results showed a high potential for reducing application rates using alternative methods compared with the traditional method. This article discusses only the deposits and coverage rate. In the next few years, biological efficacy trials are planned to confirm the advantages of the selected dosage adjustment methods.

Effect of Sodium Chloride Concentration on Growth of Paddy Rice Cultivars in the Early to the Middle Growth Stages after Transplanting

Effect of Sodium Chloride Concentration on Growth of Paddy Rice Cultivars in the Early to the Middle Growth Stages after Transplanting

Precise Postponing Nitrogen Application and Its Mechanism in Rice

Leaf ages of nitrogen application for high yield and apparent nitrogen recovery efficiency were specified through applying nitrogen fertilizer once in middle stage of growth and development using early-maturing and late japonica rice-Wuyunjing 7, Wuxiangjing 14, Changyou 1 as materials. Based on this, we studied precise postponing nitrogen application and its mechanism. Results showed that leaf ages of nitrogen application to high yield and apparent nitrogen recovery efficiency were 3rd leaf and fourth leaf from the top in early-maturing and late japonica rice. Using nitrogen in 3rd and 4th leaf from the top, made more panicles and spikelets per panicle, larger total spikelets and stable filled-grain percentage and 1000-grain weight, and lower max number of stems and tillers, higher ratio of productive tillers to total tillers, higher nitrogen accumulation, max LAI, LAD and dry matter weight in population growth and development. Yield with "PPM" (precise promoting in the middle phase) of nitrogen was significantly more than that of CK. Compared to CK, there were more significantly apparent nitrogen recovery efficiency, physiological nitrogen use efficiency, agronomic nitrogen use efficiency and yield of ear nitrogen, but lower nitrogen requirement for 100 kg grain in "PPM" of nitrogen. Mechanism of high yield and apparent nitrogen recovery efficiency in "PPM" of nitrogne was that high ratio of productive tillers to total tillers and enough population panicles were formed through consolidating population panicles and controlling non productive tillering and low effective tillering; high grain-leaf ratio (filled grains per cm2 leaf area, grain weight per cm2 leaf area), enough quantity and good quality of dry matter in heading were obtained through forming large population spikeletes, high and appropriate LAI and fine canopy structure; intense source and smooth translocation, effective sink-filling ability were enlarged through enriching dry matter accumulation after heading and coordinating producton and translocation of dry matter from population stems and sheaths.

Diel methane emissions in stands of Spartina alterniflora and Suaeda salsa from a coastal salt marsh

In this study, we aimed to understand the influence of plant type on the monthly variations of diel CH 4 fluxes from Spartina alterniflora and Suaeda salsa of coastal salt marshes at three growth stages (July, August and September). Dissolved CH 4 concentrations in porewater and sediment redox potentials were monitored, as were aboveground plant biomass and stem densities. CH 4 fluxes exhibited clear monthly variations and peaked in September in the S. alterniflora and S. salsa mesocosms. However, no discernible diel variation was observed in the CH 4 flux in the S. salsa mesocosm, probably due to its weak gas transport capacity. By contrast, notable diel variations of CH 4 flux with the peak of 1.42 and 3.67 mg CH 4 m −2 h −1 at 12:00 and the lowest of 0.75 and 2.11 mg CH 4 m −2 h −1 at 3:00 or 6:00 were observed in the S. alterniflora mesocosm on 11 August and 11 September, respectively, but not in July mainly due to low plant biomass masking diel variations in the porewater CH 4 concentration. The ratios of the maximum flux to minimum flux over the course of the day in the S. alterniflora mesocosm on 10 July, 11 August and 11 September were 1.28, 1.89 and 1.76, respectively, and corresponding values for porewater CH 4 concentration were 1.31, 1.39 and 1.17, respectively. CH 4 flux significantly correlated with CH 4 concentration in porewater, and both were significantly related to air temperature. These findings indicate that CH 4 production and CH 4 flux at the middle growth stage (August) exhibited greater responses to changes in air temperature, which in turn induced the higher diel variation. The higher diel cycle for CH 4 flux in August than in September was likely due to the higher proportion of CH 4 oxidized during diffusion within the aerenchyma system. Our results suggest that the extent of diel variations in CH 4 flux may have depended on the gas transport capacity of plants, and the highest diel variation occurred at the middle growth stage.

Photosynthetic characteristics and resource utilization efficiency of maize (Zea mays L.) and millet (Setaria italica L.) in a semi-arid hilly loess region in China

Photosynthetic characteristics and resource utilization efficiency of maize (Zea mays L.) and millet (Setaria italica L.) are studied in a loess region of China. Limited sampling shows that maize has a higher light-saturated CO2 assimilation rate, apparent quantum yield and carboxylation efficiency than does millet in the middle (July) and late (September) growth stage. Compared with millet, maize has lower transpiration rate (T r ) and stomatal conductance (G s ) in July and higher T r and G s in September. This leads to higher leaf water use efficiency in maize in July, but it is lower than for millet in September. Mass-based leaf nitrogen concentrations (N mass) of both crops are similar in both growth stages. Leaf mass per area (LMA) of maize is the same as of millet in July but lower in September. These results indicate differences in photosynthetic capacity and resource use efficiencies between these crops.

10.1007/s11475-008-1010-9

The effect of different rice plantation periods on the properties of selected soils on an alluvial plain was studied. Soils were sampled in fields cultivated for 6, 16, 26, and over forty years. In each rice cultivated and nonrice cultivated field, three soil profiles and six nearby auger holes were studied. This study indicated that continuous rice cultivation changed the soil moisture regime from xeric to aquic, the soil color from brown to grayish, and the surface horizons from mollic to ochric epipedon. With increasing duration of cultivation, the abundance of redoximorphic features increased and the soil structure changed from granular or blocky to massive. Therefore, the soil order changed from Mollisols to Inceptisols. No illuviation and eluviation of clay minerals occurred as a consequence of the rice cultivation. X-ray diffraction analysis showed that the clay minerals in the nonrice cultivated field were illite, vermiculite, montmorillonite, kaolinite, and chlorite, and, in the rice field, they were illite, montmorillonite, kaolinite, and chlorite, respectively. However, with increasing the period of cultivation, the amount of illite and vermiculite decreased while the amount of montmorillonite increased. The pH values of the saturated soil surface during the middle stage of rice growth shifted toward neutrality. The Eh of the surface horizons of the paddy soils under the field conditions were +40, −12, −84, and −122 mV, respectively, while the Eh in the nonpaddy soils were close to +90 mV. The amounts of organic matter and available Fe, Mn, Zn, and Cu increased, while the available K decreased in the paddy soils.

Reducing dislocation density in GaN films using a cone-shaped patterned sapphire substrate

The threading dislocation (TD) density in GaN films grown directly on flat sapphire substrates is typically >10 10/cm 2, which can deteriorate the properties of GaN-based LEDs significantly. This paper reports an approach to reducing the TD density in a GaN layer using a variety of patterned sapphire substrates (PSS). A cone-shaped PSS produced by metal organic chemical vapor deposition (MOVCD) was used for GaN deposition. Three types of GaN specimens were prepared at the initial nucleation stage, middle growth stage and final growth stage. The TDs generated on the cone-shaped PSS were analyzed by transmission electron microscopy (TEM) and a strain mapping simulation using HRTEM images, which evaluated the residual strain distribution. A large number of TDs were generated and the residual strain by the lattice distortions remained above the top of the cone-shaped regions. However, no TDs and residual strain were observed at the slope of the cone-shaped regions. This might be due to the formation of a GaN layer by lateral overgrowth at the slope of the cone-shaped regions, resulting in less lattice mismatch and incoherency between the GaN and sapphire. In conclusion, the TD density in the GaN layer could be reduced significantly, approximately 10 7/cm 2, using the cone-shaped PSS.

Central composite design-based analysis of specific leaf area and related agronomic factors in cultivars of rapeseed ( Brassica napus L .)

Specific leaf area (SLA) is an important parameter in evaluating leaf function, yield potential, and ecological adaptability. Data from our field experiments from 2000 to 2005 were used to evaluate the values of SLA and related agronomic factors. SLA remained stable during winter, differed significantly among the dates of observation, and declined from seedlings to maturation in all the cultivars tested. ANOVA analysis showed that SLA differed significantly with sowing date but not with the cultivar, and was correlated positively with population density but negatively with the weight of leaves, roots, and the stem and with potassium application. A parabolic relationship was found between SLA and application of phosphorus. SLA at different observation dates before anthesis was negatively correlated with shoot weight at anthesis. An appropriate combination of population density and application of phosphorus and potassium could be helpful in securing desirable values of SLA (high at the seedling stage and low from the middle growth stage to maturity) and optimal population morphogenesis and, in turn, high yields.

Impact Evaluation of Neochetina SPP. On Different Growth Stages of Waterhyacinth

An attempt was made to optimize the minimum required inoculation load of the weevils on three growth stages of waterhyacinth, based on reduction of fresh biomass, number of leaves and ramifications. The small growth stage was controlled earlier than the waterhyacinth of middle growth stage, corresponding to the increase in number of weevils per plant. The large plants could not be controlled even with the inoculation pressure of 20 weevils per plant because of high growth rate. This study suggests that Neochetina spp. has the potential to keep the population of the macrophyte at a sub- economic density, through a basic inoculation load of weevils in due course of time.

Indigenous arbuscular mycorrhiza is more important for early growth period of groundnut (Arachis hypogea L.) for P influx in an Oxisol

The contribution of indigenous arbuscular mycorrhiza (AM) on phosphorus (P) uptake by groundnut was examined in a low P field soil. The fungicide benomyl was applied to eradicate mycorrhizal infection. The treatments consisted of three P levels viz. 0, 50 and 400 mg P kg-1 soil, with and without benomyl application. Groundnut as test crop was sown two weeks after the application of benomyl and was harvested four times covering the whole growth period. At each harvest, the shoot yield, shoot P concentration, root length, soil solution P (CLi) and per cent root infection by AM was determined for benomyl treated and untreated soil at all P levels. Benomyl showed no effect on soil solution P concentration. When P was limiting, application of benomyl did reduce early groundnut growth by 40-50% at P-0, and by 25-30% at P-50. At high P supply (P-400), benomyl had little or no effect on dry matter production. Thus, indicate that the effect of benomyl on plant growth was by its influence on P uptake from soil. Phosphorus supply affected percentage of root infected by AM which was 40% of the roots at P-0, and decreased to around 30% and 10% at P-50 and P-400. In the early growing season, the P influx of maize was dependent on P in soil solution and the effect of AM was rather large. At high P supply, the contribution of AM to P influx showed a decrease. Without or low AM infection and at low P level, the P influx was 62% of that with AM. During early growth period groundnut showed a similar behaviour as maize at middle growth stage and without AM reduction of P influx, which was to an extent of 67%. In absolute terms AM is more important at maximum growth in the early growth season for groundnut. It is evident from the present investigation that AM may make an significant contribution by about 35 % to the P nutrition of groundnut, but other factors, like P solubilization by root exudates, may be even more important.

Shredded Maize Stems as an Alternative Substrate Medium

There is increased interest in the use of mixes of inorganic and organic materials as substrates in soilless culture in greenhouses, especially in parts of the world where the mixtures have not been commonly used. The potential of different ratios of shredded maize (Zea mays L.) stems as organic media on nutrient uptake, and the performance of tomato (Lycopersicon esculentum Mill.), in soilless culture, were studied. Tomato plants, cv. Belladona, were grown over a five-month period in a closed soilless culture system on four different substrates (pumice alone, shredded maize stems alone, pumice mixed with 25% or 50% maize shredded stems) and in Nutrient Film Technique, in an un-heated glasshouse. The amount of nutrient solution absorbed increased in proportion to days following transplanting, and was in part dependent on the strength of radiation and night temperature after the middle stage of growth. Plants grown on pumice + 50% maize and maize alone had similar distributions of elemental nutrient uptake. Elemental content in fruit was different only for Mn, Cu, B and Na among substrates. The ratio of number of leaves/fruit produced, favored plants grown in pumice + 50% maize, but plants grown in maize produced the greater number of fruit and the least number of leaves. No regression was observed between numbers of fruit and mean fruit weight. As nutrient uptake increased so did water uptake, with plants grown on pumice having the greater water use efficiency. The addition of maize in different ratios (25-50%) in pumice may improve its properties as a substrate for tomato soilless culture. The ratio of 50% shredded maize stems mixed with pumice could be the optimum mix for protected tomato production under the prevailing local conditions.

Indigenous arbuscular mycorrhiza is more important for early growth period of groundnut (Arachis hypogea L.) for P influx in an Oxisol

The contribution of indigenous arbuscular mycorrhiza (AM) on phosphorus (P) uptake by groundnut was examined in a low P field soil. The fungicide benomyl was applied to eradicate mycorrhizal infection. The treatments consisted of three P levels viz. 0, 50 and 400 mg P kg -1 soil, with and without benomyl application. Groundnut as test crop was sown two weeks after the application of benomyl and was harvested four times covering the whole growth period. At each harvest, the shoot yield, shoot P concentration, root length, soil solution P (CLi) and per cent root infection by AM was determined for benomyl treated and untreated soil at all P levels. Benomyl showed no effect on soil solution P concentration. When P was limiting, application of benomyl did reduce early groundnut growth by 40-50% at P-0, and by 25-30% at P-50. At high P supply (P-400), benomyl had little or no effect on dry matter production. Thus, indicate that the effect of benomyl on plant growth was by its influence on P uptake from soil. Phosphorus supply affected percentage of root infected by AM which was 40% of the roots at P-0, and decreased to around 30% and 10% at P-50 and P-400. In the early growing season, the P influx of maize was dependent on P in soil solution and the effect of AM was rather large. At high P supply, the contribution of AM to P influx showed a decrease. Without or low AM infection and at low P level, the P influx was 62% of that with AM. During early growth period groundnut showed a similar behaviour as maize at middle growth stage and without AM reduction of P influx, which was to an extent of 67%. In absolute terms AM is more important at maximum growth in the early growth season for groundnut. It is evident from the present investigation that AM may make an significant contribution by about 35 % to the P nutrition of groundnut, but other factors, like P solubilization by root exudates, may be even more important.

The influence of continuous rice cultivation and different waterlogging periods on the morphology, clay mineralogy, Eh, pH and K in paddy soils

The effect of different rice plantation periods on the properties of selected soils on an alluvial plain was studied. Soils were sampled in fields cultivated for 6, 16, 26, and over forty years. In each rice cultivated and nonrice cultivated field, three soil profiles and six nearby auger holes were studied. This study indicated that continuous rice cultivation changed the soil moisture regime from xeric to aquic, the soil color from brown to grayish, and the surface horizons from mollic to ochric epipedon. With increasing duration of cultivation, the abundance of redoximorphic features increased and the soil structure changed from granular or blocky to massive. Therefore, the soil order changed from Mollisols to Inceptisols. No illuviation and eluviation of clay minerals occurred as a consequence of the rice cultivation. X-ray diffraction analysis showed that the clay minerals in the nonrice cultivated field were illite, vermiculite, montmorillonite, kaolinite, and chlorite, and, in the rice field, they were illite, montmorillonite, kaolinite, and chlorite, respectively. However, with increasing the period of cultivation, the amount of illite and vermiculite decreased while the amount of montmorillonite increased. The pH values of the saturated soil surface during the middle stage of rice growth shifted toward neutrality. The Eh of the surface horizons of the paddy soils under the field conditions were +40, −12, −84, and −122 mV, respectively, while the Eh in the nonpaddy soils were close to +90 mV. The amounts of organic matter and available Fe, Mn, Zn, and Cu increased, while the available K decreased in the paddy soils.

A case study of infection of rice roots by deleterious fungi and minor pathogenic Pythium species in a paddy field

Roots of rice plants grown in paddy fields in a transplant culture system were collected seven times between 8 and 22 weeks after transplanting, for two crop seasons. Rice seedlings grown in a potting medium amended with the collected roots were significantly shorter than those grown in the same medium either without the addition of the roots or amended with pasteurized, collected roots indicating that seedlings were inhibited by heat-labile microorganisms on the collected rice roots. Ninety-five and 172 pure cultures of Pythium spp. and fungi, respectively, were isolated from the rice roots collected 5 or 7.5 weeks after transplanting in the fields. Among these microorganisms, Pythium aristosporum inhibited seedling growth in greenhouse experiments, and Acremonium sp., Alternaria sp., Epicoccum nigrum, Fusarium sp., Massarina sp., Penicillium spp., Rhinocladiella sp., Stemphylium sp., Trichocladium sp., and several unidentified fungi inhibited seminal root growth in in vitro experiments. These microorganisms might be involved in the inhibition of seedling growth in soils amended with the rice roots collected from the paddy field. Thus, roots of rice plants at the middle stage of growth transplanted into paddy fields can harbor pathogenic or deleterious fungi or Pythium sp(p). The effects of these microorganisms on rice growth in paddy fields are discussed.

Energy balance of irrigated intercropping field in the middle reaches of Heihe River basin

Based on the experiments conducted in an irrigated intercropping field in Zhangye Oasis in the middle reaches of Heihe River basin in 2004, the characteristics of radiation budget are analyzed. Furthermore, energy balance is cal- culated by using Bowen-Ratio Energy Balance (BREB) method. The results show that the ratio of the absorbed radiation to the incoming short radiation in intercropping crop canopy-soil system is increasing with growing stages, from 0.81 in the initial growing stage (IGS) to 0.86 in the late growing stage (LGS). The net radiation, which is smaller in IGS, in- creases rapidly in the first period of the middle growing stage (MGS) and reaches the maximum value in the second period of MGS. It then somewhat decreases in LGS. The ratio of net radiation to total radiation has a similar trend with the net radiation. In the whole growing stages, latent heat flux, which takes up 70% or so of the net radiation, is the dominant item in energy balance. Sensible heat flux shares 20% of the net radiation and soil heat flux has a percentage of 10%. The characteristics of heat balance vary distinctly in different growing stages. In IGS, the ratios of latent heat flux, sensible heat flux and soil heat flux to net radiation are 44.5%, 23.8% and 31.7% respectively. In MGS, with the in- creasing of latent heat flux and the decreasing of sensible heat flux and soil heat flux, the ratios turn into 84.4%, 6.3% and 9.3%. In LGS, the soil heat flux maintains 0W/m 2 or so, and latent heat flux and sensible heat flux take up 61.4% and 38.6% respectively. The energy balance also shows an obvious daily variation characteristic.