Transactions of the Chinese Society of Agricultural Engineering, the 1st in Agricultural Engineering, is supervised by China Association for Science and Technology, and sponsored by Chinese Society of Agricultural Engineering. It aims to introduce the latest scientific achievements and developing trends of Agricultural Engineering and provides the academic developments abroad and domestic of the discipline. The scope covers agricultural water-soil engineering, agricultural information and electrical technology, agricultural products processing engineering.
The journal is included in EI, JST, Pж(AJ), CA and CSCD.
Editor-in-Chief Zhu Ming
Deputy Editor-in-Chief Wei Xiuju Zhang Ruihong Xi Weimin Wang Liu Wang Yingkuan Li Pingping Ying Yibin Tong Jin Yun Wenju Zhao Chunjiang Kang Shaozhong
Soil thermal conductivity (
λ) is a key parameter for studying surface energy balance and coupled heat and water transfer in soil.
λ can be obtained by heat pulse method or semi-empirical or empirical models, with both models based on the information of soil texture, water content (
θ) and bulk density (
ρ
b). The pedotransfer model has the advantages of simple form and having no requirement of soil minerology information. This pedotransfer λ model, however, has not been applied comprehensively under field conditions where
λ displays strong spatial and temporal variability. The objectives of this study are to determine the spatial and temporal changes of
λ as related to
θ and
ρ
b in tilled soil layers, and to test the feasibilities of the pedotransfer
λ model for estimating field
λ with the information of soil texture,
θ and
ρ
b. Two independent field experiments were conducted: one study of different tillage treatment’s effect on
λ variations and another post-tillage soil structure dynamic study on
λ at two soil depths due to alternate wetting and drying. For the tillage method study,
λ measurements were carried out in the field, and soil cores were taken to determine
θ and
ρ
b gravimetrically. For the soil structure dynamic study,
in situ θ changes were monitored with time domain reflectometry (TDR) technique, the dynamic
ρ
b values were determined gravimetrically after each rainfall event, and the corresponding
λ data were obtained from the collected intact soil cores by heat-pulse sensors. The results showed that θ and
ρ
b were the key factors that affected
λ in tilled soil layers. In 0–10 cm soil layer, the
λ,
θ and
ρ
b values in no tillage treatment plot were significantly higher than those of the moldboard and rotary tillage plots. The soil
λ values of the 10–20 cm soil layer were higher than those in the 0–10 cm layer, and the trends were consistent with those of
θ and
ρ
b regarding tillage treatment and soil depth. For the post-tillage soil structure dynamic study,
ρ
b was increased gradually with time and soil depth and became relatively stable after four wetting/drying (W/D) cycles, i.e., from 0.98 to 1.16 g/cm
3 for the 0–5 cm layer, and from 1.09 to 1.28 g/cm
3 for the 5–10 cm layer. The magnitude of the change was relatively small among the first three W/D cycles when the degrees of saturation were relatively low, and the
ρ
b in the 5–10 cm layer reached the maximum after the fourth W/D cycle when the soil was nearly saturated, with the change became less significant thereafter. The comparison between measured and modeled values showed that the pedotransfer λ model provided reliable
λ with RMSE of 0.09 W/(m·K) and mean bias of −0.01 W/(m·K). Our analysis also highlighted the fact that when
ρ
b varied over time due to soil structure change, using a constant
ρ
b (measured either right after tillage or at the end of the experiment) would introduce larger errors for
λ estimations. The pedotransfer
λ model for estimating soil
λ could be useful for simulating the heat transfer in tilled soil layers.
In order to improve the low efficiency and high energy consumption of freezers, two kinds of nozzle structures were compared in this paper to find out the best structure that improved the intensity and uniformity of heat transfer. Due to the complexity of the freezer model, in order to simplify the test model, this study adopted the impinging freezing test bench and verified the reliability of the established models. The performance of two kinds of nozzle was analyzed and compared by using the CFD (computational fluid dynamics) numerical simulation technology. Based on the Nusselt number distribution and heat transfer uniformity on steel strip, the heat transfer characteristics on steel strip surface under the circular orifice nozzles and circular funnel nozzles at the different ratio between nozzle−to−strip distances and outlet diameters were analyzed. The results show that when the
H/D
E is in the range of 2−12, the average Nusselt number
on steel strip surface under the circular funnel nozzle is about 5.41%−15.10% higher than
under the circular orifice nozzle. The change of the Nusselt number on steel strip surface under both two kinds of nozzle structures is greatly influenced by the
H/D
E and is less affected by the cross flow. The heat transfer uniformity
η on steel strip surface under the circular funnel nozzle is about 7.06%−34.52% lower than that of the circular orifice nozzle, and the airflow in the air impinging freezer is relatively uniformity. By comparing the structures of two nozzles, we find that the steel strip surface with circular funnel nozzle under the same air supply volume has higher Nu and better heat transfer uniformity, which is beneficial to reduce the freezing time, increase the output of the air impinging freezer, and improve the quality of the frozen food.
Irrigation and nitrogen fertilization are two major factors influencing the grain yield production in agroecosystem, and appropriate irrigation and nitrogen fertilizer application can improve the grain yield and water use efficiency by alleviating the stress of drought and nutrient deficiency, enhancing the photosynthetic area and photosynthetic rate. In this study, we investigated the impacts of precipitation year patterns on crop yield, water consumption and their relationship under different water and nitrogen management practices. A field experiment during 2011–2014 was conducted with 3 irrigation levels and 4 nitrogen input levels in Guanzhong Plain of Shaanxi Province. The irrigation levels included no irrigation, 46 mm irrigation at the jointing stage, and 46 mm irrigation at the jointing and wintering stages, respectively. The nitrogen input levels included nitrogen application rates of 0, 105, 210, and 315 kg/hm
2, respectively. The fertilizer was urea. The other field managements followed local traditional methods. The experiment was carried out with complete randomized design. The soil water content and grain yield were measured and the water use efficiency was calculated as the ratio of yield to ET
a under various water and nitrogen managements in different year patterns. Meanwhile, the soil water storage was calculated based on the volumetric water content. ET
a was calculated by the field water balance equation. The results showed that the soil water content before sowing was affected by irrigation, nitrogen fertilizer application rate and precipitation. The soil water content before sowing increased as more irrigation and less nitrogen application rate were applied. The 0–100 cm soil water content before sowing would be mainly supplemented when the total precipitation from July to September was below 400 mm, and the 0–180 cm soil water content before sowing increased by 0.47 mm as the total precipitation from July to September increased by 1 mm. The 0–180 cm soil water storage after harvest improved with more irrigation but decreased first and then leveled at a certain value as more nitrogen was used; it was greatly effectd by the precipitation two months before harvest. The water consumption increased with more irrigation while the effects of nitrogen and interaction of irrigation and nitrogen on water consumption were not significant; it had a linear relationship with the water input during the growth period with the coefficients being effected by the initial soil water conditions,
i.e., less water would be consumed by unit water input when the soil water storage before planting was higher. Irrigation enhanced both the yield and actual water consumption, while the yield was only improved significantly in the relatively dry year in 2012–2013 and the water use efficiency was not boosted in all years. Nitrogen fertilization had no significant effect on water consumption but improved the yield and water use efficiency significantly, which showed that the nitrogen application rate increased the proportion of crop transpiration to total water consumption. In addition, the maximum (boundary) yield and water use efficiency were explored by developing a boundary function of winter wheat yield and evapotranspiration in Guanzhong Plain. From the function, we found that when the water consumption exceeded 388 mm, the grain yield would level at 8 184 kg/hm
2 and the maximum water use efficiency was 2.52 kg/m
3. In this research, the interaction of water, nitrogen and precipitation year pattern on yield and field water consumption was analyzed, aiming at providing valuable information for developing reasonable water and fertilizer management practices in winter wheat production.
For studying the transient response state and movement state of apricot fruits during different stages of exfoliation, a dynamic model of apricot fruit–branch double pendulum hanging on a single long branch according to the actual growth of apricot fruit is established in this paper. The apricot fruit–branch separation conditions are analyzed theoretically, and the physical parameters of Kumai apricot fruit at ripening stage are measured. The whole forced vibration process of the target fruits is recorded using 2 high-speed cameras with same specifications perpendicular to the xoz plane and the yoz plane, and the relevant data such as shedding time, speed, and acceleration are obtained. Theoretical analysis and experiments show that the apricot fruit–fruit branch double pendulum system mainly shows 3 kinds of motion states: fruit branches drive fruits to swing, fruit branches drive fruits to twist and fruit swing. The average weight of the ripe fruit of Kumari apricot is 14.26 g, the average external dimensions are 28.84 mm in length, 27.93 mm in width, and 27.83 mm in thickness; the average surface hardness of mature fruits is 9.17 kg/cm
2; the average connection force of ripe fruit–branches is 2.923 N. Based on the measured spatial coordinates of the fruit in the
xoz and
yoz planes and Phantom Camera Control 3.1 high-speed video control software analysis, the whole spatial motion track of apricot fruits is nearly elliptical from vibration to shedding, the total time from vibration to shedding of target fruits is 0.322 s, and the maximum speeds of the relative static origin of apricot fruits are 0.112 and 0.166 m/s when being dropped in spatial planes
xoz and
yoz. The instantaneous speeds of the apricot fruit before shedding are 1.53 and 1.359 m/s, respectively, and the accelerations are 765 and 679.98 m/s
2, respectively. Using MATLAB software, the velocity data of fruits in different planes
xoz and
yoz are compared with the Fourier fitting curves of velocity and time relative to stationary origin, and the fitting curve of the speed of apricot fruits during vibration shedding and the corresponding function are obtained. The
R2 values of the fitting function are 0.970 4 and 0.986. Through analyzing the speed function curve, the process of fruit vibration shedding can be divided into 3 periods: 0 to 0.148 s, 0.148 to 0.248 s, and 0.248 to 0.322 s. In the third stage, the fruit has already fallen off before it reaches the full cycle. To ensure the accuracy of the analysis, the analysis of the velocity function in the first 2 stages with complete vibration period shows that, in the
xoz plane, the velocity fitting functions
R2 of the first 2 stages are 0.965 2 and 0.952 5, respectively, the speed change period is 0.15 s and the function amplitude is 0.021 m/s; the velocity fitting functions
R2 in the first 2 stages of the
yoz plane are 0.954 5 and 0.981 1, respectively, and the speed change period is 0.13 s; the amplitude of the second stage function is twice that of the first stage, which is 0.054 and 0.027 m/s, respectively. The vibration cycle of the apricot fruit-fruit branch double pendulum system is close to the period of the excitation cycle. According to the calculation of the fruit weight of mature apricot, the shedding force components produced by acceleration on each plane are 11.22 and 9.7 N respectively, both of which are greater than the average connected force between mature apricot fruit and stalk. Based on the above characteristics of fruit vibratory shedding, this study can provide a theoretical basis for clarifying the shedding mechanism during fruit harvesting, optimizing the design parameters of apricot vibrating harvesters, and improving the fruit recovery rate.
