Yield and growth characteristics for cotton under various irrigation regimes on sandy soil

Over-watering cotton wastes a valuable and scarce resource; it can also lead to rank growth, nutrient leaching, and contaminated groundwater. Since under-watering can decrease yields, the question becomes one of finding the optimum application regime. An irrigation experiment was set up to apply water at six different application rates, ranging from 33% to 144% of normal, with hopes of identifying the regime that produces maximum yield. Two cultivars, Acala Maxxa and Acala PhytoGen-72 (Gossypium hirsutum L.), were planted on sandy soil and irrigated daily with a highly efficient subsurface drip irrigation system for four seasons. The results showed that on the average there was no significant difference in the yield of the two cultivars and there was no significant difference in the yield for the three wettest treatments. The driest of the three wettest treatments, treatment 4, was a critical point on the water production function curve. It represented the least amount of water applied that still produced essentially maximum yield, and it had the highest water use efficiency. This critical level of water application during mid-season was found to be, on the average, 95% of Class A pan evaporation; it corresponded to a total seasonal application of 654 mm of water. Any application less than this critical level decreased yields. Reducing the water application by 5% below the critical level caused about a 4.6% reduction in yield. The critical level produced a soil moisture level that remained nearly constant throughout the season. The final plant height was closely related to the depth of water applied, with the wettest treatment producing plant heights of 2.0 m, and the driest treatment producing plant heights of 0.6 m. At the extremes of the water application rates there were some small differences in the early-season growth rate of the plants, but the main cause of differences in final plant height was the date of cutout (cessation of main stem node production). The length of season for the driest treatment was about 4 weeks shorter than for the wettest treatment on both cultivars. Results showed that deficit irrigation of cotton on sandy soil can greatly reduce yield, and the practice should probably be avoided.     

Precision of soil moisture sensor irrigation controllers under field conditions

New soil moisture sensor systems (SMSs) for irrigation control have been commercialized in recent years. However, limited research has been carried out to evaluate their precision to measure the volumetric soil water content (θ). The objectives of this research were to: (a) determine the relationship between θ and the θ sensed by four commercially available SMSs, (b) quantify the proportion of scheduled irrigation cycles (SICs) that the SMSs bypassed, and (c) determine the θ at which SICs were allowed or bypassed. Sensors from brands Acclima, Rain Bird, Irrometer, and Water Watcher were buried at 7-10 cm depth, on plots with common bermudagrass [Cynodon dactylon (L.) Pers.]. A calibrated ECH₂O probe was also installed in every plot, at the same depth, to monitor θ continuously. When comparing the ECH₂O readings with θ sensed by the SMSs, significant correlations were found for the three Acclima RS500 (AC) systems tested, and for two of the three systems of Irrometer Watermark 200SS/WEM (IM) and Rain Bird MS-100 (RB). Most of the SMS-based treatments bypassed the majority of the SICs during rainy periods, and allowed irrigation during the dry periods. On average, 71% of the SICs were bypassed by the SMS treatments, without detriment to the turfgrass quality. However, most of the SMSs were not found to be precision instruments, because sometimes they bypassed SICs and sometimes they did not, even when reading the same or a lower θ. Considering the average θ range of over which the different SMS treatments always allowed or always bypassed irrigation, brand AC resulted in the significantly narrowest range (1.4%) followed by RB (3.2%), suggesting that they were more consistent and precise in measuring θ than Water Watcher DPS-100 (WW) and IM (7.4 and 7.8%, respectively). These results are consistent with the reported water savings achieved by these SMSs in related studies.     

Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes

Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.     

Prediction of soil moisture characteristics from mechanical analysis and bulk density data

Soil moisture characteristics can be established directly from the physical properties of soils such as mechanical analysis and bulk densities. Multiple regression equations were worked out by taking first fractions of sand (E₁), silt + clay (E' = E₂ + E₃) and bulk density (P), and second fractions of sand (E₁), silt (E₂), clay (E₃) and bulk density (P) as independent variables to predict the parameter b, the air-entry potential ψ_e and the saturation moisture content _s of the soil-moisture characteristics equation. Regression equations were tested for soils of different textural and structural compositions and showed good agreement between estimated and experimentally determined values.     

Effect of soil moisture regimes on the yield and water use of lentil (Lens culinaris Medic)

Summary The effect of soil moisture regimes on the grain and straw yield, consumptive water use (Cu) and its relation with evaporation from free water surface (Eo), water use efficiency and soil moisture extraction pattern of lentil was studied in a field experiment conducted at the Indian Agricultural Research Institute, New Delhi during the fall-spring season of the crop years 1979–1980 and 1980–1981. The grain and straw yield, consumptive water use rate, Cu/Eo ratio and water use efficiency increased with an increase in irrigation frequency. Consumptive water use rate increased as the crop season advanced and reached its peak value during flowering and grain filling stage. The Cu/Eo ratio attained its minimum values 35 and 105 days after sowing at branching and grain filling stages. Depletion of soil moisture was most from the top 0–30 cm soil layer followed by 30–60 cm soil layer and was least from 90–120 cm soil layer. The pattern of soil moisture depletion was also influenced by soil moisture regime. During the vegetative and flowering stage the percent contribution from the top 0–30 cm soil layer decreased and that from the lower soil layers (30–60, 60–90, and 90–120 cm) increased with an increase in the soil moisture tension, however, the actual amount of moisture depleted from all the soil layers was always higher under low soil moisture tension regime than under high soil moisture tension regime. During the grain development stage the soil moisture treatment had no significant effect on the relative contribution from different soil layers under low and high soil moisture tension as the crop was irrigated at the same time under both these treatments. However, with no irrigation, the percent contribution from top soil layer continued to decrease, and from lower soil layers continued to increase, as the crop advanced from flowering stage to grain development stage.     

TRIZ辅助马铃薯收获机薯土分离输送装置创新设计

针对马铃薯收获机薯土分离输送装置存在薯土分离不充分、伤薯率高等问题,应用TRIZ理论对薯土分离输送装置进行创新设计;基于系统功能分析识别薯土分离输送装置的功能缺陷,应用物场模型、技术矛盾、物理矛盾等TRIZ工具求解创新方案,设计一种具有双抖动单元和降运抖动筛面的薯土分离输送装置。基于输送筛面上薯土秧混合物的力学分析,确定筛面倾角范围为β≤32°;结合理论分析和生产实际确定一阶升运筛面倾角为20°、二阶升运筛面倾角为16°、降运抖动筛面倾角10°、抖动单元振幅为21 mm、分离筛杆条间距为50 mm、各阶筛面输送有效长度分别为450 mm、600 mm、1 000 mm 和100 mm。通过升运分离筛和降运分离筛抖动筛面的运动学分析对比,验证创新方案的合理性。     

Water use of young ‘Fuji’ apple trees at three soil moisture regimes in drainage lysimeters

Studies were conducted during 4 months of each growing season in 1994 and 1995 to measure water use of young apple trees (Malus domestica Borkh. cv ‘Fuji’) growing under different soil moisture regimes in temperate climate conditions and to evaluate monthly crop coefficients of such conditions. To do so, double pot lysimeters under a transparent rain shield were designed and installed. The three soil moisture regimes in three replicates each were: (A) drip-irrigation at −50 kPa of soil matric potential (IR50); (B) drip-irrigation at −80 kPa of soil matric potential (IR80); and (C) constant shallow water table at 0.45 m below the soil surface (WT45). In each treatment, soil surface was maintained with or without turf grasses. Monthly water use was not different in drip-irrigated treatments (IR50 and IR80), but greatest in the WT45 treatment. Monthly crop coefficients increased linearly in time for drip-irrigated apple trees (r² values of 0.76^*** for IR50 and of 0.77^*** for IR80), while those obtained in the WT45 treatment fluctuated. Leaf water potential (LWP) of drip-irrigated trees was similar until 63 days after treatment (DAT), but the values for IR80 trees began to decline thereafter. The LWP of WT45 trees decreased from 48 DAT. Temporal variations in leaf water content (LWC) was similar to that of LWP, except for two abrupt decreases in IR80 trees. The LWC of WT45 trees began to decrease from 59 DAT, and this occurred 2 weeks after the reduction in LWP. Average shoot length of IR50 trees was greater than that of IR80 and WT45 trees. The results of this study provided water use and crop coefficients for apple trees in relation to soil moisture regimes under temperate climate.     

Dielectric coated water content reflectometer for improved monitoring of near surface soil moisture in heavily fertilized paddy field

Mat rush (Juncus effusus L.), used for ‘Tatami’ (a traditional Japanese mat), is a type of crop requiring a large amount of fertilizer (450–600 kg ha⁻¹ of N). In a heavily fertilized mat rush paddy field we examined the monitoring of soil water content (θ) by using the water content reflectometer (WCR). WCR sensors with and without coating rods were prepared and tested for their performance in different solutions. In addition, these sensors for Gley Lowland Soils were also calibrated for measuring θ. The results showed that the measured water content using the uncoated WCR, increasing with the EC of the solution, was 1.6 times of that for distilled water while the output for the coated WCR became 1.04 times. The coating prevents conduction losses while it influences the sensitivity of the WCR sensor. The monitoring of θ using both coated and uncoated WCR sensors in a mat rush paddy field was conducted throughout a cropping season. For the coated sensors, water content could be determined accurately even after fertilizer applications, while with the uncoated sensors it was overestimated. Thus, it was concluded that the use of insulated WCR sensors make it possible to accurately monitor the near surface soil moisture in a heavily fertilized paddy field.     

Simulation of soil moisture profiles for scheduling of irrigations

A mathematical model for simulating soil water content in the root zone was developed by taking into consideration soil physical properties, crop and climatic parameters. The governing differential equation for unsaturated flow of water in the soil was solved numerically using the Crank-Nicholson finite difference technique. The water uptake by plants was simulated by using two different sink functions. The model predictions were in good agreement with field data and thus it is possible to schedule irrigations.     

Effects of drip irrigation frequency on soil wetting pattern and potato growth in North China Plain

The effect of irrigation frequency on soil water distribution, potato root distribution, potato tuber yield and water use efficiency was studied in 2001 and 2002 field experiments. Treatments consisted of six different drip irrigation frequencies: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days), with total drip irrigation water equal for the different frequencies. The results indicated that drip irrigation frequency did affect soil water distribution, depending on potato growing stage, soil depth and distance from the emitter. Under treatment N1, soil matric potential (ψ_m) Variations at depths of 70 and 90 cm showed a larger wetted soil range than was initially expected. Potato root growth was also affected by drip irrigation frequency to some extent: the higher the frequency, the higher was the root length density (RLD) in 0–60 cm soil layer and the lower was the root length density (RWD) in 0–10 cm soil layer. On the other hand, potato roots were not limited in wetted soil volume even when the crop was irrigated at the highest frequency. High frequency irrigation enhanced potato tuber growth and water use efficiency (WUE). Reducing irrigation frequency from N1 to N8 resulted in significant yield reductions by 33.4 and 29.1% in 2001 and 2002, respectively. For total ET, little difference was found among the different irrigation frequency treatments.     

Macroscopic scale soil moisture dynamics model for a wheat crop

Summary A numerical soil moisture dynamics model was developed for; wheat crop using either observed or generated root length densities with root sink incorporating diminishing rate of water uptake by plant roots due to decreasing soil moisture in drying cycles and loss of absorptive power of roots due to ageing. The simulated soil moisture contents were overestimated by 6.0 and 9.6% on an overall basis by the model when observed and generated root length densities were used, respectively, in comparison to observed moisture contents. The model using generated root length densities simulated less water uptake in comparison with the model which utilized observed root length densities.     

A comparison of soil moisture sensors for space flight applications

Plants will be an important part of future long-term space missions. Automated plant growth systems require accurate and reliable methods of monitoring soil moisture levels. There are a number of different methods to accomplish this task. This study evaluated sensors using the capacitance method (ECH2O), the heat-pulse method (TMAS), and tensiometers, compared to soil water loss measured gravimetrically in a side-by-side test. The experiment monitored evaporative losses from substrate compartments filled with 1- to 2-mm baked calcinated clay media. The ECH2O data correlated well with the gravimetric measurements, but over a limited range of soil moisture. The averaged TMAS sensor data overstated soil moisture content levels. The tensiometer data appeared to track evaporative losses in the 0.5- to 2.5-kPa range of matric potential that corresponds to the water content needed to grow plants. This small range is characteristic of large particle media, and thus high-resolution tensiometers are required to distinguish changing moisture contents in this range.     

保水剂对冬小麦不同生育阶段土壤水分及利用的影响

为探明保水剂施用后对冬小麦不同生育阶段水分利用的作用机理,在豫西丘陵旱作区,通过大田试验,研究了保水剂对冬小麦不同生育阶段的保水、作物的耗水特征、水分利用效率等的影响。结果表明：保水剂提高了冬小麦不同生育阶段0～100 cm土层的土壤含水量、促进了生物量的积累、降低了小麦耗水量、提高了小麦产量和水分利用效率。各处理中,60和90 kg/hm2处理的土壤含水量及储水量均较其他处理高,而耗水量最低。播种-拔节期,保水剂用量越高干物质积累越显著;拔节-孕穗期及灌浆-收获期,60 kg/hm2处理较对照增加的干物质量最高;而孕穗-灌浆期,30 kg/hm2干物质量增加最为显著。各生育阶段,除孕穗-灌浆期外,60 kg/hm2处理的水分利用效率均较高。最终,60 kg/hm2处理的产量和水分利用效率均最高,较对照增产47.4%,水分利用效率增加10.6 kg/(mm·hm2)。     

不同水分处理下液膜覆盖对夏玉米生长及产量的影响

针对塑料地膜对农业生产造成的严重污染问题,运用对照处理方法,探讨了液体地膜覆盖对夏玉米生长发育及产量等方面的影响。结果表明,液膜覆盖使夏玉米株高和茎粗均比对照偏大,其中,低水分处理下差异最为显著。夏玉米叶面积指数低水分处理时液膜覆盖在生育前期较对照偏大,生育后期偏小;而中、高水分下液膜覆盖叶面积指数在整个生育期内均比对照偏大。液膜覆盖使夏玉米光合速率和蒸腾速率显著增大,有利于光合产物的形成。低水分处理下液膜覆盖增产效果最好,增产率达到56.97%,产投比为1.695,高水分下液膜覆盖增产效果最差,增产率仅为15.57%,液膜覆盖产投比小于对照。研究认为,夏玉米液膜覆盖能有效抵抗干旱逆境从而达到节水增产的显著效果。     

马铃薯联合收获薯土分离技术与装置研究

马铃薯主粮化战略的实施使得国内更加重视马铃薯行业的发展,马铃薯全程机械化、自动化受到更多关注。马铃薯联合收获是其生产过程中的重要一环,而决定收获质量的关键就是薯土分离技术。为进一步了解和掌握国内外薯土分离技术的研究现状,进行综述分析,并重点阐述带杆振动式、振摆结合式、拨动式、旋转式四种不同分离技术的结构原理以及联合收获中的二次薯土分离形式,并对目前联合收获中薯土分离装置的应用做了介绍,明确马铃薯联合收获薯土分离环节当前的主要问题是分离效果和块茎损伤之间的矛盾关系。从不同土壤类型、不同种植区域对薯土分离技术装置的设计思路进行分析,并从智能化、复合型、绿色化三个方面对未来进行展望,以期对从事相关研究的学者提供一定的参考。     

不同沟垄覆盖下土壤水热效应对旱作马铃薯生长及产量的影响

针对宁南山区春季降雨少、低温不利于马铃薯出苗,而作物生育中后期高温胁迫限制马铃薯块茎形成导致减产等问题,于2016年设置垄覆地膜沟内覆盖塑料地膜(DM)、玉米秸秆(JG)、生物降解膜(SM)、麻纤维地膜(MM)、液态地膜(YM)及沟不覆盖(BM),以传统平作为对照(CK),研究沟垄覆盖模式对土壤温度、土壤水分、旱作马铃薯生长及块茎产量的影响.结果表明:处理DM,SM,MM和YM马铃薯生育期耕层土壤温度表现出增温效应,而处理JG和BM表现为降温效应,其中处理DM增温效果和处理JG降温效果最佳.处理YM,JG对马铃薯生长前期保水效果较好,分别较CK显著提高13.3%,27.0%,而处理JG,DM对生育中后期的保墒效果较佳,分别较CK显著提高22.4%,13.2%.处理JG可显著促进马铃薯生长,其增产效果最为显著,DM次之,分别较CK增产47.8%,44.8%,其他处理较CK差异不具有统计学意义.可见,在宁南山区实施垄覆地膜沟覆秸秆模式可调控土壤水热环境,对旱作马铃薯生长及增产效果最佳.     

Root growth, available soil water, and water-use efficiency of winter wheat under different irrigation regimes applied at different growth stages in North China

Field experiments were conducted at the Luancheng Agro-Ecosystem Experimental Station of the Chinese Academy of Sciences during the winter wheat growing seasons in 2006-2007 and 2007-2008. Experiments involving winter wheat with 1, 2, and 3 irrigation applications at jointing, heading, or milking were conducted, and the total irrigation water supplied was maintained at 120 mm. The results indicated that irrigation during the later part of the winter wheat growing season and increase in irrigation frequency decreased the available soil water; this result was mainly due to the changes in the vertical distribution of root length density. In ≤30-cm-deep soil profiles, 3 times irrigation at jointing, heading, and milking increased the root length density, while in >30-cm-deep soil profiles, 1 time irrigation at jointing resulted in the highest root length density. With regard to evapotranspiration (ET), there was no significant (LSD, P < 0.05) difference between the regimes wherein irrigation was applied only once at jointing; 2 times at jointing and heading; and 3 times at jointing, heading, and milking. Compared with 1 and 3 times irrigation during the winter wheat growing season, 2 times irrigation increased grain yield and 2 times irrigation at jointing and heading produced the highest water-use efficiency (WUE). Combining the results obtained regarding grain yield and WUE, it can be concluded that irrigation at the jointing and heading stages results in high grain yield and WUE, which will offer a sound measurement for developing deficit irrigation regimes in North China.     

Combining remote sensing and in situ soil moisture data for the application and validation of a distributed water balance model (HIDROMORE)

An application of the FAO56 approach to calculate actual evapotranspiration (AET) and soil moisture is reported, implemented by means of the HIDROMORE computerized tool, which performs spatially distributed calculations of hydrological parameters at watershed scale. The paper describes the application and validation of the model over 1 year in an area located in the central sector of the Duero Basin (Spain), where there is a network of 23 stations for continuous measurement of soil moisture (REMEDHUS; Soil Moisture Measurement Stations Network) distributed over an area of around 1300 km². The application integrated a series of Landsat 7 ETM+ images of 2002, from which the NDVI series (Normalized Difference Vegetation Index) and the map of land covers/uses were derived. Validation consisted of the use of the REMEDHUS soil moisture series and their comparison with the series resulting from the application. Two simulations were performed, with soil parameters values at the surface (0-5 cm depth) and at the mean of the profile scale (0-100 cm depth). The behaviour of the simulated soil moisture was described by means of its correlation with the measured soil moisture (determination coefficient, R² = 0.67 for the surface values and 0.81 for the mean profile values), and the Root Mean Square Error (RMSE), resulting in a range of it for the 23 stations between 0.010 and 0.061 cm³ cm⁻³. The application afforded an underestimation of the soil moisture content, which suggests the need for a redefinition of the limits of the plant available water used in the calculation. The results showed that HIDROMORE is an efficient tool for the characterization of hydrological parameters at global scale in the study zone. The combination of the FAO56 methodology and remote sensing techniques was efficient in the spatially distributed simulation of soil moisture.     

Evapotranspiration relationship with pan evaporation and evapotranspiration ratio of corn under different nitrogen levels and moisture regimes

In a field experiment with four moisture regimes and eight nitrogen levels, the ratios between evapotranspiration and pan evaporation ($\text{Et}\text{Eo}$) were low in the initial stages of crop growth and attained maximum values at 70–80% (20 and 40% available soil moisture depletion (ASMD)), 65% (60% ASMD) and 55% (80% ASMD) of the crop growth stage. Amongst nitrogen levels, the evapotranspiration ratio (ETR) was highest (3573) under no nitrogen and lowest (1312) with 180 kg N/ha. The 20% ASMD regime utilised less water (ETR= 1499 to produce a kilogram of grain than did the other moisture regimes. The lowest evapotranspiration ratio (914) was recorded with 20% ASMD and 180 kg N/ha in combination. The highest ETR (3954) was found with 60% ASMD and no nitrogen. An additive effect of nitrogen and moisture was found, in indicating that they can be substituted one for the other, when one of them becomes a constraint.     

Distribution of water and salt in soil under trickle and pot irrigation regimes

An ellipitical clay pot was buried vertically in the centre of a lysimeter as a means of supplying water to the soil. The distribution of water and salt in the soil emerging from the pot source was compared with that under trickle irrigation. Five hundred milliequivalents of calcium chloride was applied to the soil by both methods. Calcium chloride was subsequently leached by applying 50 l of tap water. The soil solution was sampled periodically using suction cups. Soil samples were also taken for measurements of water content and chloride ion concentration. Water applied at the rate of 130 ml/h by the pot moved the salt to a radial distance of 41.5 cm in 390 h, but applying water by trickle at the rate of one l/h moved the salt 42 cm in 52.5 h. For an equal amount of water applied, salt moved deeper in the profile at the lower application rate. More salt spreading was observed from the trickle source with higher application rate. After 72 h of redistribution, the wetted volumes were approximately equal for trickle and pot irrigation regimes.