卧式密集烤房烟叶烘烤干筋期放置引风板的研究

[目的]考察在卧式密集烤房出风口处放置引风板对缩短烤烟干筋期的烘烤时间的影响。[方法]试验在烟叶烘烤干筋初期(干球温度56℃时)在卧式密集烤房出风口处设置引风板,提高烤房后段的温度及风速,从而使主筋前后干燥一致,缩短烟叶在烘烤后期的烘烤时间。[结果]研究得出,烘烤一炉上、中、下3个部位烟叶,设置引风板的烤房处理比未设置引风板的烤房对照分别缩短烘烤时间12~25 h,节省煤炭75~110 kg,节省用电量20~40 kW·h。[结论]研究可为卧式密集烤房在烟叶生产中的进一步推广应用提供参考依据。     

单组分快速湿固化聚氨酯木材胶黏剂的研制

针对30min内胶接桦木生材(含水率在60%～90%)集成木方的生产需要,采用聚醚多元醇、多亚甲基多苯基多异氰酸酯(P-MDI)为主要原料制备单组分快速湿固化聚氨酯木材胶黏剂,以表(?)时间,常温凝胶时间和干、湿状压缩剪切强度为指标,通过正交试验确定合成工艺的主要参数:—NCO:—OH摩尔比值(R)大小、聚乙二醇(PEC)分子量大小和溶剂量与增塑剂量的比例,探讨了各项因素对胶黏剂性能的影响,并根据实际生产需要,优化出最佳方案。结果表明:所合成胶黏剂压制桦木生材集成木方的主要性能指标,均超过日本JISK6806—2003Ⅰ类板的标准要求。     

Effect of bulk density and soil water tension on denitrification in the rhizosphere of spring wheat (Triticum vulgare

Summary Pot experiments were carried out to study the influence of bulk density (D _b), soil water tension (pF) and presence of plants (spring wheat) on denitrification in a low-humus B_t-horizon of a udalf. Pots of only 5-cm depth were found to be most suitable for the experiments when using the acetylene inhibition method. Almost homogeneous soil compaction between 1.1 and 1.6g soil cm^–3 was achieved by a Proctor tamper. Water tensions were adjusted by means of ceramic plates on which negative pressure was applied. No denitrification was detected in unplanted pots. With planted pots and increasing bulk density denitrification increased more in pots with 14-day-old plants than in pots with 7-day-old plants. With 14-day-old plants N₂O emission pot^–1 increased steadily from 2 mol at D _b 1.1 to 8 mol at D _b 1.6, when soil moisture was adjusted to pF 1.5, although root growth was impaired by higher bulk density. From an experiment with different bulk densities and water tensions it could be deduced that the air-filled porosity ultimately determined the rate of denitrification. When low water tension was applied for a longer period, water tension had an overriding effect on total denitrification. Denitrification intensity, however, i.e. the amount of N₂O g^–1 root fresh weight, was highest when low water tension was accompanied by high bulk density. The results suggest that the increase in denitrification intensity at oxygen stress is partly due to higher root exudation.     

装烟密度对密集烘烤过程中烟叶主要生理指标的影响

采用河南农业大学设计的电热式温湿自控密集烤箱,对不同装烟密度和变黄温度下烟叶的淀粉酶、过氧化物酶(POD)、抗坏血酸过氧化物酶(AAO)及叶绿素的动态变化作了探索性研究。结果表明:整个烘烤过程中,装烟密度为5 5～6 5kg/m3的处理烟叶淀粉酶、过氧化物酶、抗坏血酸过氧化物酶的活性相对较高,叶绿素含量最低     

Identification of RAPD markers linked to nut weight and plant stature in cashew

Cashew is an important edible nut crop of tropics. Bulk segregant analysis (BSA) was carried out on DNA bulks constituted from F₂ population and germplasm in order to link or associate molecular markers with economic characters. In all 458 RAPD, 31 ISSR and 21 pairs of SSR primers were used and identified polymorphic markers between parents. Though screening F₂ bulks with these markers identified markers polymorphic between the bulks but none could be validated with the individuals of their bulks. Hence screening with germplasm bulks was carried out and could identify four RAPD markers polymorphic between the bulks for nut weight and plant stature and also between the individuals of their bulks. Of the four, three markers were associated with nut weight amplifying at 775, 475, 275, bp region in primers OPN 14, UBC 184 and UBC 185 respectively. Out of these three, two markers were specific to low nut weight and one marker was specific to high nut weight and their bands were present in greater frequency (50–77.8% and 75%) of individuals constituting the respective bulks. Similarly, the another marker UBC 185₂₇₅ was detected which was specific to low plant stature and was present in 66.7% and 10% individuals constituting short and tall bulks respectively. Markers identified with bulks and with the individuals of bulks were validated further with more individuals of F₂ and germplasm.     

Hydro-physical responses of gypseous and non-gypseous soils to livestock grazing in a semi-arid region of NE Spain

Pasture productivity depends on soil hydro-physical properties, which in turn are deeply affected by livestock grazing. However, the comparative response of different soil types, and particularly gypseous soil types, to grazing has hardly been studied before. This paper compares the effect of grazing on the soil hydro-physical properties of silty gypseous (Gy) and non-gypseous (NGy) soils located in a semi-arid region (Middle Ebro Valley, NE, Spain). Two different soil managements were selected: ungrazed natural shrubland (N) and grazed shrubland (GR) soils. The gypsum, CaCO₃ and organic matter content (OM), soil texture, soil bulk density (ρ_b), penetration resistance (PR), saturated sorptivity (S), hydraulic conductivity (K), and the water retention curve (WRC) for undisturbed soil samples from 1 to 10 cm depth soil layer were measured. The ρ_b and PR in NGy soils were significantly higher than those observed in the Gy ones. Soil compaction due to grazing treatment tended to increase ρ_b and decrease the K and S values. While no differences in PR were observed in the Gy soils between grazing treatments, the PR measured in the NGy soils under GR was significantly higher than the corresponding values observed under N. Differences in K and S between GR and N treatments were only significant (p < 0.05) in NGy soils, where K and S values under the N treatment were almost four times greater than the corresponding values measured under GR. Overall, no differences in the WRCs were observed between soil types and grazing treatments. While the WRCs of NGy soils were not significantly affected by the grazing treatment, Gy soils under N treatment present a significantly higher level of soil macropores than under GR treatment. The hydro-physical features of Gy soils tended to be less affected by grazing than those of the NGy soils. These results suggest that livestock grazing, in both Gy and NGy soils, has a negative effect on the physical soil properties, which should be taken into account by land managers of these semi-arid regions where silty gypseous and non-gypseous areas coexist.     

The contribution of rock fragments to the available water content of stony soils: Proposition of new pedotransfer functions

The contribution of rock fragments to the soil available water content (SAWC) of stony soil has been quantified by measurements of bulk density and gravimetric water content at different water potentials on rock fragments of different lithologies: flints, cherts, chalks, gaizes and limestones. More than 1000 pebbles (2 cm < equivalent diameter of the rock fragment < 5 cm) have been sampled in stony soils developed from each of the five lithologies. We demonstrated that the water content at saturation of the studied pebbles was equal to the water content at −100 hPa and to the water content at field capacity. A linear relationship between the water content at −100 hPa and at −15,840 hPa enabled to derive a simple pedotransfer function to determine the available water content of the rock fragments. We also proposed a second simple pedotransfer function, which expresses the available water content from the dry bulk density of the rock fragments only. A simulation at the horizon scale for a loamy-clay stony horizon showed that the SAWC could be strongly misjudged when the rock fragments were not taken into account: for a stony horizon containing 30% of pebbles, the SAWC is underestimated by 5% for chert pebbles and by 33% for chalk pebbles.     

Development of on-line measurement system of bulk density based on on-line measured draught, depth and soil moisture content

On-line measurement of soil compaction is needed for site specific tillage management. The soil bulk density (ρ) indicating soil compaction was measured on-line by means of a developed compaction sensor system that comprised several sensors for on-line measurement of the draught (D) of a soil cutting tool (subsoiler), the soil cutting depth (d) and the soil moisture content (w). The subsoiler D was measured with a single shear beam load cell, whereas d was measured with a wheel gauge that consisted of a swinging arm metal wheel and a linear variable differential transducer (LVDT). The soil w was measured with a near infrared fibre-type spectrophotometer sensor. These on-line three measured parameters were used to calculate ρ, by utilising a hybrid numerical–statistical mathematical model developed in a previous study. Punctual kriging was performed using the variogram estimation and spatial prediction with error (VESPER) 1.6 software to develop the field maps of ρ, soil w, subsoiler d and D, based on 10 m × 10 m grid. To verify the on-line measured ρ map, this map was compared with the map measured by the conventional core sampling method.

The spherical semivariogram models, providing the best fit for all properties was used for kriging of different maps. Maps developed showed that no clear correlation could be detected between different parameters measured and subsoiler D. However, the D value was smaller at shallow penetration d, whereas large D coincided with large ρ values at few positions in the field. Maps of ρ measured with the core sampling and on-line methods were similar, with correlation coefficient (r) and the standard error values of 0.75 and 0.054 Mg m⁻³, respectively. On-line measured ρ exhibited larger errors at very dry zones. The normal distribution of the ρ error between the two different measurement methods showed that about 72% of the errors were less than 0.05 Mg m⁻³ in absolute values. However, the overall mean error of on-line measured ρ was of a small value of 2.3%, which ensures the method accuracy for on-line measurement of ρ. Measurement under very dry conditions should be minimised, because it can lead to a relatively large error, and hence, compacted zones at dry zones cannot be detected correctly.     

Effect of different tillage systems on the quality and crop productivity of a clay–loam soil in semi-arid north-western Turkey

A 2-year study was conducted to investigate the effect of three tillage systems on the properties of clay–loam soil (EutricVertisol) planted with winter wheat (Triticum aestivum L.) in the Canakkale province of north-western Turkey. Crop productivity was also evaluated. The three tillage treatments were: (1) conventional tillage involving mouldboard ploughing followed by two discings (MT); (2) shallow tillage consisting of rototilling followed by one discing (RT); (3) double discing (DD). In the first year of the study, bulk density (BD) was found significantly lower under RT at both 0–10 and 10–20 cm depths with 1.24 and 1.32 Mg cm⁻³, respectively, when compared to MT treatment. However, MT at 20–30 cm provided the highest BD, at 1.49 Mg cm⁻³. In the second year of the study, DD had the lowest BD at all depths followed by RT and MT. Based on the 2-year mean, aggregate size distribution (ASD) and mean weight diameter (MWD) were significantly influenced by tillage treatments. The greatest MWD was obtained with DD, followed by MT and RT. Increasing MWD and coarse aggregates decreased seedling emergence. Organic carbon increased after RT, DD, and MT by 58%, 30%, and 18%, respectively, when compared to the amount at the beginning of the study. Similarly, the total N in the soil and straw was higher after RT than the other treatments. At 1.76 MPa, penetration resistance at 18–30 cm was significantly higher during the growing period using DD, followed by RT with 1.35 MPa and MT with 1.33 MPa. There was no significant difference between treatments at 0–18 cm. Increasing OC and total N and decreasing BD and PR under RT increased grain yield to 4611 kg ha⁻¹, followed by MT and DD at 4375 and 4163 kg ha⁻¹, respectively, according to the 2-year mean.     

A new approach for modelling vertical stress distribution at the soil/tyre interface to predict the compaction of cultivated soils by using the PLAXIS code

Soil compaction by agricultural machines can have adverse effects on crop production and the environment. Different models based on the Finite Element Method have been proposed to calculate soil compaction intensity as a function of vehicle and soil properties. One problem when modelling soil compaction due to traffic is the estimation of vertical stress distribution at the soil surface, as the vertical stress is inhomogeneous (non-uniform) and depends on soil and tyre properties. However, uniform stress distribution at the soil/tyre interface is used to predict the compaction of cultivated soils in most FEM compaction models. We propose a new approach to numerically model vertical stress distribution perpendicular to the driving direction at the soil/tyre interface, employing the FEM models of PLAXIS code. The approach consists of a beam (characterised by its geometric dimensions and flexural rigidity) introduced at the soil surface and loaded with a uniform stress with the aim to simulate the action of a wheel at the soil surface. Different shapes of stress distribution are then obtained numerically at the soil surface by varying the flexural rigidity of the beam and the mechanical parameters of the soil. PLAXIS simulations show that the soil type (soil texture) modifies the shape of the stress distribution at the edges of the contact interface: a parabolic form is obtained for sand, whereas a U-shaped is obtained for clay. The flexural rigidity of the beam changes the shape of distribution which varies from a homogenous (uniform) to an inhomogeneous distribution (parabolic or U-shaped distribution). These results agree with the measurements of stress distributions for different soils in the literature. We compared simulations of bulk density using PLAXIS to measurement data from compaction tests on a loamy soil. The results show that simulations are improved when using a U-shaped vertical stress distribution which replaces a homogenous one. Therefore, the use of a beam (cylinder) with various flexural rigidities at the soil surface can be used to generate the appropriate distribution of vertical stress for soil compaction modelling during traffic.