Yaohu Kang

Effects of different irrigation regimes on the growth and yield of drip-irrigated potato

Potato (Solanum tuberosum L.) is a relatively sensitive plant to water stress and is widely planted in Japan. Soil water is one of most important factors affecting the yield and quality of potatoes. Under a rain-shelter, an experiment was conducted to evaluate the effects of different amounts of drip irrigation water on the potato growth, tuber yield, size and specific gravity. The amount of irrigation water applied was 0.25, 0.50, 0.75, 1.00 and 1.25 times of water surface evaporation (Ep) measured by a standard 0.2 m diameter pan (K=0.25, 0.50, 0.75, 1.00 and 1.25). Plant height, biomass and shoot water content increased, but the specific leaf weight (SLW, g/m2) decreased with increasing amount of irrigation water. The amount of irrigation water had significant effects on decreasing the canopy temperature. Total fresh tuber yields and marketable tuber yields (>85 g) increased with increasing amount of irrigation water. The highest yield was obtained at the 1.25 times regime and the total tuber yield was close to the theoretical maximum. Irrigated water increased yields not only by increasing tuber number, but also by increasing the mean weight of the tubers. Irrigated water increased potato tuber quantity, but decreased potato tuber quality. The specific gravity of potato tubers tended to decrease as water applied increased, and the scarred and the hollow-heart potato tubers increased with increasing amount of irrigation water. So, under controlled environmental conditions, potatoes should be irrigated using pan evaporation factor more than 0.75 (K>0.75) that is a guideline. The use of lower pan factor (K<0.75) may reduce potato tuber yield significantly.

Soil Salinity Changes Under Cropping with Lycium barbarum L.and Irrigation with Saline-Sodic Water

In order to utilize the wasted saline-sodic soils under shallow groundwater condition, a 3-year field study was carried in a field cropped with Lycium barbarum L. and irrigated by drip irrigation with saline groundwater under the water table depth of 30-40 cm in the northern Yinchuan Plain, China. Effects of cropping duration (one, two, and three years) on soil salinity, soil solution composition, and pH in three adjacent plots were investigated in 2008. Results showed that a high irrigation frequency maintained high soil water potential and subsequently facilitated infiltration and downward movement of water and salt in the crop root zone. Salt accumulated on the edges of the ridges, and soil saturated-paste electrical conductivity (ECe) was higher in the edge. Concentrations of Na(+), Ca(2+), Mg(2+), Cl(-), and SO(4)(2-) in the soil increased with the soil depth as did the ECe, while FICO(3)(-) and pH had a relative uniform distribution in soil profile. As planting year increased, the ECe and soil salts in the field had a decreasing tendency, while in the root zone they decreased immediately after irrigation and then remained relatively stable in the following growing seasons. HCO(3)(-) and pH had little change with the planting year. Results suggested that the application of drip irrigation with saline water could ameliorate saline-sodic soil and provide a relatively feasible soil environment for the growth of salt-tolerant plant Lycium barbarum L. under the saline-sodic soils with shallow groundwater.

Design of microirrigation laterals at minimum cost

Abstract Based on the design methods of finite elements and golden-section searches, a method was developed for designing microirrigation laterals at minimum cost. Characteristics of water application uniformity as affected by lateral diameters and lengths were analyzed. When the required average emitter discharge is known, the relationships of water application uniformity, best submain position (paired laterals), and operating pressure head as a function of the lateral diameter and length can be accurately determined using a personal computer. The lateral diameter and length can then be determined from a contour map representing water application uniformity as a function of the lateral diameter and length (computer calculation). The best submain position and operating pressure head for this lateral diameter and length is then determined by computer calculation. This method is suitable for designing microirrigation laterals on both uniformly and nonuniformly sloping fields.

Effect of Sprinkler Irrigation on Field Microclimate

A field experiment was conducted to study the effect of sprinkler irrigation on field microclimate, yield and water use efficiency during winter wheat growing period from Oct. 27, 2000 to June 8, 2001 in Yucheng Comprehensive Experimental Station, Chinese Academy of Sciences. The experiment results show that sprinkler irrigation affects the air temperature and humidity near crop canopy not only at the sprinkler day but also during the whole sprinkler irrigation season. The effect of sprinkler irrigation on temperature and vapour pressure is more significant during daytime. Air temperature inversion appears for a very long time and air temperature is decreased sharply near canopy under sprinkler irrigation condition. Vapor pressure is enhanced under sprinkler irrigation condition. The average vapor pressure under sprinkler irrigation condition is 1.42, 1.01, 1.36 and 1.20 mb higher than that under surface irrigation condition at heights of 1, 2, 3 and 4 m, respectively. Diurnal soil temperature amplitude under sprinkler irrigation condition is smaller than that under surface irrigation condition at ground surface. The temperature amplitude decreases sharply as depth increases under both sprinkler irrigation and surface irrigation conditions. The average soil temperature difference between sprinkler irrigation and surface irrigation is not significant at ground surface. However, soil temperature under sprinkler irrigation condition is higher than that under surface irrigation when it is deeper than 5 cm. Cumulative water surface evaporation measured using 20 cm standard pan on the top of canopy from April 1 to June 4 under sprinkler irrigation is 355.7 mm, which is 42.5 mm lower than that under surface irrigation condition. Total water uses during winter wheat growing period were 436.5 and 459.4 mm under both sprinkler irrigation and surface irrigation conditions, respectively. However, the winter wheat yield under sprinkler irrigation is 6430 kg.ha-1, and it is 4455 kg.ha-1 under surface irrigation condition. Water use efficiency (WUE) of winter wheat in sprinkler irrigation field is 1.47 kg.m-3 while it is 0.97 kg.m-3 under surface irrigation condition. WUE under sprinkler irrigation condition is higher than that under surface irrigation condition about 52%.

Use of a New Controlled-Loss-Fertilizer to Reduce Nitrogen Losses during Winter Wheat Cultivation in the Danjiangkou Reservoir Area of China

ABSTRACT The use of a new controlled-loss-fertilizer (CLF) to reduce nitrogen loss from the Danjiangkou Reservoir of China was explored. Specifically, a three-year experiment was conducted to identify the optimum fertilizer rate for CLF used in wheat production. The treatments included four CLF levels, 20% (20% F), 35% (35% F), 50% (50% F), and 100% (100% F), of the local recommended fertilization dose (LRFD), and traditional fertilizers with the same dose as 50% F as the control (CF). Treatment 50% F with an equivalent fertilizer rate decreased nitrogen (N) runoff loss and leaching loss by 21.6% and 24.5%, while leading to a 9.8% increase in soil residual mineral N when compared to CF. Treatments 50% F and 100% F produced higher wheat yield than the other treatments. At the same fertilizer rate, the grain yield of the 50% F treatment was 5.5% higher than that of CF. Regression analysis of the yield relative to the CLF rate revealed that the optimum CLF rate was about 77% of the LRFD. Overall, the results indicate that CLF with 77% of the LRFD could be the optimum rate for minimizing nitrogen loss and increasing yield and should be considered for wheat production in the area.

Root Water Uptake Model Considering Soil Temperature

A field experiment was carried out to research the effect of soil temperature distribution on root water uptake in soil water simulation. Soil temperature distribution patterns under border irrigation and surface drip irrigation were researched. The root water uptake model was modified based on the effect of soil temperature on root water uptake. Results showed soil temperature profile distribution was greatly influenced by irrigation method. The range of temperature was larger under border irrigation, with the temperature being 3-6°C higher in 0-20 cm depth than in 20-100 cm depth. Except for the top layer under surface drip irrigation, mean soil temperature showed the trend of exponential decay throughout the soil profile. The relationship between temperature and water uptake rate was expressed in exponential function. With the modification of the root water uptake model as affected by temperature profile distribution, the value of the root mean square error between the simulated and observed soil water decreased from approximately 0.04 to 0.02 in the top layer under border irrigation, but showed no obvious difference under surface drip irrigation. When soil temperature differed greatly in the top layer from the deep layer, the root water uptake model considering soil temperature could improve the precision of soil water simulation. The results indicated that the modified root water uptake model could be used to simulate soil water dynamics. DOI: 10.1061/(ASCE)HE.1943-5584.0000642.

Effect of operating pressures on microirrigation uniformity

Abstract The effect of operating pressure heads on water application uniformity in microirrigation submain units was evaluated. Research results show that water application uniformity either increases or slightly decreases as operating pressure head increases in a range when the emission exponent x ≤ 0.5 in most cases. The water application uniformity decreases as operating pressure head increases in a range when the emission exponent x > 0.5. The relationship between operating pressure head and average emitter discharge in submain units can be considered as approximately linear for operating pressure heads in a small range (usually between the allowable minimum and maximum operating pressures of the submain units). These results help to estimate the average emitter discharge rate easily in a submain unit for an increased or decreased operating pressure head when one is attempting to manage emitter discharge dynamically according to the requirements of crop root growth for different periods. Generally, a microirrigation system designed to meet the desired uniformity of water application according to the allowable minimum operating pressure head would be better when x ≤ 0.5 because water application uniformity increases as operating pressure increases if emitter discharges are being managed dynamically. However, a microirrigation system designed to meet the required water application uniformity according to the allowable maximum operating pressure head would be better when x > 0.5 because, in general, water application uniformity increases as operating pressure decreases.

Effects of different irrigation methods on micro-environments and root distribution in winter wheat fields

The irrigation method used in winter wheat fields affects micro-environment factors, such as relative humidity (RH) within canopy, soil temperature, topsoil bulk density, soil matric potential, and soil nutrients, and these changes may affect plant root growth. An experiment was carried out to explore the effects of irrigation method on micro-environments and root distribution in a winter wheat field in the 2007–2008 and 2008–2009 growing seasons. The results showed that border irrigation (BI), sprinkler irrigation (SI), and surface drip irrigation (SDI) had no significant effects on soil temperature. Topsoil bulk density, RH within the canopy, soil available N distribution, and soil matric potential were significantly affected by the three treatments. The change in soil matric potential was the key reason for the altered root profile distribution patterns. Additionally, more fine roots were produced in the BI treatment when soil water content was low and topsoil bulk density was high. Root growth was most stimulated in the top soil layers and inhibited in the deep layers in the SDI treatment, followed by SI and BI, which was due to the different water application frequencies. As a result, the root profile distribution differed, depending on the irrigation method used. The root distribution pattern changes could be described by the power level variation in the exponential function. A good knowledge of root distribution patterns is important when attempting to model water and nutrient movements and when studying soil-plant interactions.

Effects of water application intensity of microsprinkler irrigation on water and salt environment and crop growth in coastal saline soils

Laboratory and field experiments were conducted to investigate the effects of water application intensity (WAI) on soil salinity management and the growth of Festuca arundinacea (festuca) under three stages of water and salt management strategies using microsprinkler irrigation in Hebei Province, North China. The soil water content (e) and salinity of homogeneous coastal saline soils were evaluated under different water application intensities in the laboratory experiment. The results indicated that the WAI of microsprinkler irrigation influenced the e, electrical conductivity (ECe) and pH of saline soils. As the WAI increased, the average values of e and ECe in the 0-40 cm profile also increased, while their average values in the 40-60 cm profile decreased. The pH value also slightly decreased as depth increased, but no significant differences were observed between the different treatments. The time periods of the water redistribution treatments had no obvious effects. Based on the results for e, ECe and pH, a smaller WAI was more desirable. The field experiment was conducted after being considered the results of the technical parameter experiment and evaporation, wind and leaching duration. The field experiment included three stages of water and salt regulation, based on three soil matric potentials (SMP), in which the SMP at a 20-cm depth below the surface was used to trigger irrigation. The results showed that the microsprinkler irrigation created an appropriate environment for festuca growth through the three stages of water and salt regulation. The low-salinity conditions that occurred at 0-10 cm depth during the first stage (-5 kPa) continued to expand through the next two stages. The average pH value was less than 8.5. The tiller number of festuca increased as SMP decreased from the first stage to the third stage. After the three stages of water and salt regulation, the highly saline soil gradually changed to a low-saline soil. Overall, based on the salt desalinization, the microsprinkler irrigation and three stages of water and salt regulation could be successfully used to cultivate plants for the reclamation of coastal saline land in North China.

Urease activity and its relationships to soil physiochemical properties in a highly saline-sodic soil.

To ascertain the levels of urease activities (UA) and their relationships with soil physicochemical properties in salt-affected soils during reclamation, soil transects of a saline-sodic soil with different planting years under drip irrigation were intensively sampled. An enhanced soil UA in root zone (0-40 cm beneath drip emitter) was found as the planting years increased. In all transects, soil UA ranged from 0.38 to 8.53 mu g NH4+-N released g(-1) dry soil h(-1) at 37 degrees C, and showed a large spatial variability within transect. R-2 of multiple regressions increased gradually with planting years, indicating that variations in UA could be better predicted after amelioration. Path analysis showed that the negative direct effects of soil pH on UA were clearly dominant, with the direct path coefficients of -0.357 similar to -0.666 (p < 0.05). Soil organic matter yielded greater positive indirect path coefficients through pH and total nitrogen. An exponential relationship was found between soil UA and pH values (p < 0.01). Our findings demonstrate that after the cultivation under drip irrigation for 3 years, soil biological activities and fertility level increased, with the decrease of soil salinity and sodicity.