A simulation study of chickpea crop response to limited irrigation in a semiarid environment

In West Asia and North Africa (WANA) including northwest (NW) Iran irrigation is becoming increasingly available and investigation of the effect of limited irrigation (LI) is a research need. Only a few seasons of successful experimentation exist with LI effects. Thus, the objective of this simulation study was to examine potential long-term benefits of limited irrigation in NW Iran in terms of grain yield. To do this, a simple, mechanistic chickpea (Cicer arietinum L.) model and 16 years of weather data of Maragheh (NW Iran) were used. Three LI systems with one, two and three irrigations and each with three plant population densities (25, 38 and 50 plants m⁻²) were simulated. Results showed chickpea crop experiences terminal drought stress that is started at a time between flowering and beginning seed growth (BSG). This terminal drought stress severely reduces grain yield by 67%, from 2766 kg ha⁻¹ under full-irrigated conditions to 909 kg ha⁻¹ under rainfed conditions. Grain yield was significantly increased with LI compared to rainfed conditions. Grain yields were reached to 60, 75 and 90% of grain yield simulated under full-irrigated (generally requires five irrigations) conditions. In LI with one irrigation its application at BSG, and in LI with two and three irrigations, application of first irrigation at flowering and application of one or two other irrigations when fraction of transpirable soil water dropped to 0.5 in the root zone resulted in higher grain yield. Water use efficiency was, also, increased with LI by 28, 39 and 52% for one, two and three irrigations, respectively. In LI systems with two and three irrigations it was required to a higher plant density (38 or 50 plants m⁻²) to capture and to use applied water more efficiently.     

Spatial variability of rainfall and yield of maize in a semiarid region

The influence of nonuniform rainfall distribution patterns on the variability of maize yield and soil water use was studied with the aid of the analyses of rainfall and evapotranspiration data of a semiarid region. The analyses enabled us to define homogeneous areas of soil water availability through the application of a geostatistic algorithm developed for the computation of semivariograms, autocorrelograms and crosscorrelation functions.Water economy and yield of nonirrigated maize grown at each homogeneous area is evaluated through the application of a modification of Hanks' yield—evapotranspiration model.To optimize rainfall use by the crop under semiarid conditions, the effect of differences in soil water availability and maize varietal responses to water stress are evaluated. Results indicate that, when these differences are considered in the selection of maize cultivars, a significant increment in total regional production can be expected.     

Estimating reference evapotranspiration with atmometers in a semiarid environment

Reference evapotranspiration (ET₀) estimations require accurate measurements of meteorological variables (solar radiation, air temperature, wind speed, and relative humidity) which are not available in many countries of the world. Alternative approaches are the use of Class A pan evaporimeters and atmometers, which have several advantages compared to meteorological stations: they are simple, inexpensive and provide a visual interpretation of ET₀. The objectives of the study were to compare the evaporation from atmometers (ET_gage) with the evapotranspiration estimated by the FAO-56 Penman-Monteith equation (ET_0PM) and to evaluate the variability between three modified atmometers of a commercial model. Comparison between daily ET_gage measured by the atmometer and ET_0PM showed a good correlation. However, ET_gage underestimated ET_0PM by approximately 9%. Differences between ET_gage and ET_0PM ranged from −2.4 to 2.2 mm d⁻¹ while the mean bias error was −0.41 mm d⁻¹. Underestimations occurred more frequently on days with low maximum temperatures and high wind speeds. On the contrary, atmometer overestimations occurred on days with high maximum temperatures and low wind speeds. Estimates of ET₀ using the atmometer appeared to be more accurate under non-windy conditions and moderate temperatures as well as under windy conditions and high temperatures. Atmometers 2 and 3 overestimated the evaporated water by atmometer 1 with a maximum variability of cumulative water losses of 4.5%. A temperature-based calibration was performed to improve the atmometer accuracy, using maximum temperature as an independent variable, with good results.     

Crop coefficient for drip-irrigated cotton in a Mediterranean environment

A 3-year study was conducted in the eastern Mediterranean region of northern Syria to develop crop coefficient, K _c, for drip-irrigated short-season cotton (Gossypium hirsutum L.). Two sets of K _c curves were determined, the generalized K _c published by the UN’s Food and Agriculture Organization (FAO) that was adjusted for local climate, and the locally developed K _c as the ratio of measured cotton evapotranspiration to calculated reference evapotranspiration. The adjusted FAO K _c curves were the same for the 3 years. However, the locally developed K _c curves not only differed among the 3 years, but also from the adjusted FAO K _c. During the mid-season stage, the adjusted FAO K _c was 24% higher than the locally developed value of 1.05. Variations in locally developed K _c values were caused by normal year-to-year variations in irrigation timing and amount, suggesting sensitivity of K _c that cautions against the use of locally developed K _c based on limited data (i.e., a single season). On the season, the overestimation of crop evapotranspiration by using adjusted FAO K _c was substantial and equivalent to 150 mm water or about two additional irrigations per season. Results caution against blind application of published FAO K _c curve, suggesting some local or regional calibration for increased accuracy.     

Regional calibration of Hargreaves equation for estimating reference ET in a semiarid environment

The Hargreaves equation provides reference evapotranspiration (ET_o) estimates when only air temperature data are available, although it requires previous local calibration for acceptable performance. This equation has been evaluated under semiarid conditions in Southern Spain using data from 86 meteorological stations, comparing daily estimates against those from the FAO-56 Penman–Monteith equation, which was used as standard. Variability of results among location was clearly apparent, with MBE ranging from 0.74 to −1.13 mm d⁻¹ and RMSE from 0.46 to 1.65 mm d⁻¹. Maxima under- and overestimation amounted to 24.5 and 22.5%, respectively. In general, larger under- and overestimations occurred in stations located close to the coast and at inland areas, respectively. Yearly means of windspeed (V) and daily temperature range (ΔT) fairly influenced the accuracy of the equation. It was more accurate for windy locations with large ΔT, and for locations with light wind conditions combined with low to moderate values of ΔT. According to the values taken by V and ΔT, the stations were represented by points on the ΔT–V coordinate plane, in which four regions were delimited. A regional calibration was carried out considering only temperature and wind conditions. Correction was not necessary for stations located within two of them; for the other two regions, new values for the empirical coefficient of the equation are suggested (0.0027 and 0.0021). After correction, average RMSE and maximum and minimum MBE decreased substantially (12, 24 and 41%, respectively), and 74 out of the 86 locations gave quite accurate results, with relative values of MBE lower than 10% in most cases. Alternatively, another method based on kriging interpolation was proposed to obtain, for each individual station, locally adjusted values for the empirical coefficient as a function of the same variables. This second correction procedure behaved even better than the first one. There was a 15% improvement in the average RMSE, and maximum and minimum MBE values decreased 50 and 70%, respectively. At all locations, relative values of MBE were less than 10% and in 70% of them were lower than 5%. Validation was done by using data from 14 meteorological stations for other Spanish regions, and the consequences from the application of the corrections proposed for an irrigation district are discussed.     

Comparison of soil water content and corn yield in furrow and conventional ridge sown systems in a semiarid region of China

Water deficits and unusually warm soil temperatures can adversely affect conventional ridge sown systems. Increasingly serious water and temperature issues associated with global climate change may be problematic in the future, particularly in semiarid regions. This study explored the soil water and crop yield benefits of switching the sowing location of corn from ridges to furrows. Experiments were conducted over three years. Corn was grown in shallow furrow (SF) and deep furrow (DF) sown treatments until the V8 stage (eight visible leaf collars). New ridges were then built over the existing furrows. Grain yield was found to be higher in the SF and DF sown treatments than in a conventional ridge sown treatment (CR), especially in drought years. Switching sowing position from ridge to furrow could increase corn yield, directly, by improving soil moisture early in the growing season and, indirectly, by stimulating the growth of resource-capturing organs (e.g., leaves and roots). This simple and efficient approach to crop production in semiarid climates may be practical for the management of numerous agricultural systems, particularly those that are resource-limited, with greater vulnerability to the effects of global climate change.     

Crop yield and soil water restoration on 9-year-old alfalfa pasture in the semiarid Loess Plateau of China

The alfalfa pastureland in the semiarid Loess Plateau region of Northwest China usually has dry soil layers. A field experiment was conducted from October 2000 to October 2004 to examine soil water recovery and crop productivity on a 9-year-old alfalfa pasture. This experiment included six treatments: alfalfa pasture for 10-14 years, a conventional farming system without prior alfalfa planting, and four alfalfa-crop rotation treatments. For the rotation treatments, after 9 years of alfalfa selected crops were planted from 2001 to 2004 in the following sequence: (1) millet, spring wheat, potatoes, peas; (2) millet, corn, corn, spring wheat; (3) millet, potatoes, spring wheat, corn; (4) millet, fallow, peas, potatoes. The results showed that dry soil layers occurred in alfalfa pasture. We then plowed the alfalfa pasture and planted different crops. The soil water gradually increased during crop growth in the experimental period. The degree of soil water recovery in the four alfalfa-crop rotation treatments was derived from comparison with the soil water in the conventional system. After 4 years, the soil water recovery from the alfalfa-crop rotation systems at 0-500 cm soil depth was 90.5%, 89.8%, 92.2% and 96.7%, respectively. Soil total N content and soil respiration rate were high in the alfalfa-crop rotation systems. The yields of spring wheat in 2002, peas in 2003 and potatoes in 2004 in the alfalfa-crop rotation systems were not significantly different from yields in the conventional system. In the alfalfa-crop rotation systems, the yields of spring wheat and peas were greatly influenced by rainfall and were lowest in the dry year of 2004; the yields of corn and potatoes had a direct relationship with water use and were lowest in 2003. In summary, soil water in dry soil layers can recover, and crop yields in the alfalfa-crop systems were equal to those of the conventional system.     

Accuracy of the Bowen ratio-energy balance method for measuring latent heat flux in a semiarid advective environment

The Bowen Ratio-Energy Balance (BREB) is an accurate method often used to measure the latent heat flux (λE) due to its simplicity and portability. However, its performance in advective areas is less clear and its accuracy may depend on the equality of eddy transfer coefficients for heat and water vapor. In this work, hourly measured λE of a reference crop (Festuca arundinacea Schreb.) using a BREB system was compared with lysimeter-measured λE under moderate to severe advective conditions. The lysimeter resolution for hourly records was 22.6 W m⁻². The analysis of the eddy transfer coefficients was made using simultaneous measurements of fluxes and vertical gradients of temperature and humidity. To avoid computational problems when β→ −1, some hourly periods were discarded in the analysis. Rejected data amounted to 37% of the total, although the cumulative evapotranspiration (ET) during these hours did not exceed 13% of the total ET. The BREB method overestimated daily ET by an average of 5.5% and by 5.7% when only daylight hours were considered. Under stable atmospheric conditions the method was less accurate, with relative errors of 21% vs. 11% under unstable conditions. For daylight hours, accuracy was higher under unstable conditions (RMSE = 36.15 W m⁻²) than under stable conditions (RMSE = 50.20 W m⁻²), which had larger overestimations of ET (6.3 vs. 5.1%). The main source of error appears to come from insufficient fetch resulting in local advective conditions. Nevertheless, and from a purely practical perspective, under the advective conditions of these measurements the BREB technique provides accurate ET fluxes with limited errors.     

Deficit irrigation in maize for reducing agricultural water use in a Mediterranean environment

Research on crop response to deficit irrigation is important to reduce agricultural water use in areas where water is a limited resource. Two field experiments were conducted on a loam soil in northeast Spain to characterize the response of maize (Zea mays L.) to deficit irrigation under surface irrigation. The growing season was divided into three phases: vegetative, flowering and grain filling. The irrigation treatments consisted of all possible combinations of full irrigation or limited irrigation in the three phases. Limited irrigation was applied by increasing the interval between irrigations. Soil water status, crop growth, above-ground biomass, yield and its components were measured. Results showed that flowering was the most sensitive stage to water deficit, with reductions in biomass, yield and harvest index. Average grain yield of treatments with deficit irrigation around flowering (691 g m⁻²) was significantly lower than that of the well-irrigated treatments (1069 g m⁽²). Yield reduction was mainly due to a lower number of grains per square metre. Deficit irrigation or higher interval between irrigations during the grain filling phase did not significantly affect crop growth and yield. It was possible to maintain relatively high yields in maize if small water deficits caused by increasing the interval between irrigations were limited to periods other than the flowering stage. Irrigation water use efficiency (IWUE) was higher in treatments fully irrigated around flowering.     

The effects of irrigation regimes and nitrogen rates on some agronomic traits of canola under a semiarid environment

This study was aimed to investigate dual effects of irrigation regimes and N fertilizer rates on some agronomic traits (with emphasis on yield qualitative and quantitative characteristics) and finding optimized irrigation level and N application rate for two canola (Brassic napus L.) cultivars. For this purpose, two variety of canola (Zarfam and Modena), four irrigation regimes including 30%, 45%, 60% and 75% (I1-I4) of maximum allowable depletion (MAD) of available soil water (ASW) and four nitrogen rates (viz. 0, 90, 180 and 270 kg N ha⁻¹ (N1-N4) were involved in Karaj, Iran for two successive years (2007-2008). Our results revealed special fertilizer threshold for each irrigation regime in respect to seed yield. Response rate to fertilizers was ceased in lower fertilizer rates by prolonging irrigation. The response rate showed a decrease of 15.4%, 17.2% and 30.7% in I2, I3 and I4 in comparison with I1, but I2 response to fertilizer ceased in higher N rate as N_critical (189.8 kg N ha⁻¹). This implies that I2 improved response of canola cultivars to N fertilizer, which was accompanied by its higher WUE. Also, all estimated N_criticals for all irrigation levels were higher than the current recommendation of 130 kg N ha⁻¹. This show the capability of increasing canola cultivars yield in study region by reasonable increasing of fertilizer rate (decreasing gap between recommended N rate and estimated values) in advisable irrigation regime (I2). Cultivars tended to respond similarly to irrigation and nitrogen for seed yield in both years, but Zarfam was more efficient than Modena in respect to response to diverse treatments.     

Cotton response to non-uniformity of conventional sprinkler irrigation

Sprinkler irrigation systems are characterized by some degree of non-uniformity. The effect of non-uniformity on crop yield has been modelled in different ways but experimental studies are scarce. An experiment was conducted comparing the effects of two levels of uniformity (mean Wilkox and Swailes' uniformity coefficients of 80% and 52%) at two levels of water supply (about 400 and 260 mm for the whole irrigation season) on cotton production. Final yield was not affected either by uniformity or by the amount of water supplied. Vegetative growth was higher in the full irrigation treatments. Maximum leaf area index did not differ statistically between uniformity treatments. The lack of differences was attributed to the curvilinear shape of the yield function and to the dampening of the variations in applied water in the soil, as the coefficient of variation in applied water was more than twice the coefficient of variation of infiltrated water. These results suggest that non-uniformity of conventional sprinkler irrigation has a lower impact on cotton crop performance than expected from previous simulation studies. Received: 1 March 1996     

Genotypic differences of maize in grain yield response to deficit irrigation

This study was undertaken to investigate genotypic differences of five maize cultivars in grain yield response to two different modes of deficit irrigation, conventional deficit irrigation and partial root zone irrigation. Three irrigation treatments were implemented: (1) FULL irrigation, the control treatment where plant water requirement, 100% Class-A pan evaporation, was fully met and the furrows on both sides of the plant rows were irrigated; (2) partial root zone irrigation (PRI), 35% deficit irrigation, compared to FULL treatment, was applied in every other furrow thus irrigating only one side of the plant rows. The furrows irrigated were alternated every irrigation; (3) conventional deficit irrigation (CDI), the same amount of water as PRI was applied in furrows on both sides of the plant rows, similar to FULL irrigation treatment. Five maize cultivars (P.31.G.98, P.3394, Rx:9292, Tector and Tietar) showing extreme growth response to water stress were selected out of ten cultivars tested with earlier completed greenhouse-pot experiment. A split-plot experimental design, comprising three irrigation treatments and five maize cultivars with four replicates, was used during two years of work, in 2005 and 2006. Total of nine irrigations, with one-week irrigation interval, were annually applied using a drip-irrigation system. Soil water status was monitored using a neutron moisture gauge, in addition to measuring leaf water potential and above-ground biomass production throughout the growing season. Grain yield and other yield attributes were measured at harvest as well as assessing differences in plant root distributions. Decrease in grain yield and harvest index of the tested cultivars, compared to FULL treatment, was proportionally less under PRI than CDI. Whether or not a significant yield advantage can be obtained under PRI compared to CDI showed significant (P < 0.05) genotypic variability. Tector and Tietar among the tested cultivars of maize showed significantly higher grain yield (P < 0.05) under PRI than CDI. The yield advantage of the genotypes (P.3394 and Tector) under PRI compared to CDI seems related to their enhanced root biomass developed under PRI.     

Yield, water and nitrogen-use response of rice to zeolite and nitrogen fertilization in a semi-arid environment

Water scarcity and soil nitrogen (N) loss are important limitations for agricultural production in semi-arid region especially for rice production. Zeolite (Z) as a soil conditioner can be used to retrain water and nitrogen in near-surface soil layer in lowland rice production system. The objectives of this study were to investigate the effects of different application rates of natural zeolite (clinoptilolite) and nitrogen on rice yield, yield components, soil nitrogen, water use, water productivity in a silty clay soil in 2004 and 2005. Zeolite was only applied in the first year. In order to study the long-term and continuous effect of zeolite on the objectives of the study, no zeolite was applied in the second year and the study was conducted on the same land as the first year. Zeolite and N were applied at rates of 0, 2, 4, and 8 t ha⁻¹ and 0, 20, 40, and 80 kg ha⁻¹, respectively in 2004. In 2005, each plot received the same amount of N as received in 2004. It is concluded that by decreasing N application rates, higher Z application rate is needed to improve grain yield. Highest grain yield was obtained at N application rate of 80 kg ha⁻¹ and Z application rate of 4 t ha⁻¹. Higher grain yield was mostly attributed to lower unfilled grain percentage and higher 1000-grain weight that were a result of higher N application rate and N retention in soil due to Z application. Nitrogen and Z applications resulted in higher grain protein contents and nitrogen recovery efficiency (NRE). Based on these results and due to higher N retention in soil under Z application, improved grain yield quality, nitrogen-use efficiency (NUE), and nitrogen recovery efficiency (NRE) could be obtained at Z application rate of 8 t ha⁻¹ and N application rate of 80 kg ha⁻¹ or more. However, this was not satisfied for NUE. Moreover, it is found that at higher N application rates lower Z application rates are needed to effectively retain soil residual mineral nitrogen. Furthermore, at N application rates of 80 kg ha⁻¹ or more, Z application increased soil water retention and resulted in lower seasonal water use and higher water productivity. In general, it was concluded that the effect of Z application in retaining soil N was also effective in the second year.     

Reduced water consumption of dormant-seeded sugar beet in a semiarid climate

Dormant seeding refers to sowing spring crop species in fall. In the spring, seedlings start growing and the crop is established before spring sowing is normally completed. A dormant-seeded crop can establish quickly in spring and may escape from early season drought. A study was conducted to compare performances of dormant seeding with early and late spring seeding of sugar beet. Field experiments were carried out in the Khorasn province (NE of Iran) in 2002 and 2003 by growing a bolting resistant variety (BR1). The experiment consisted of a randomized complete block design with four replications. Dormant seeding was subjected to six irrigation treatments in addition to an early and late spring seeding. The first irrigation was applied 0, 10, 20, 30, 40 and 50 days after 60% soil moisture depletion. After harvest, root yield, sugar concentration, white sugar yield, and non-sugar components of the root samples were measured and analyzed. The results of the dormant seeding showed that root yield of sugar beet decreased with increasing delay of irrigation at the early stages of plant growth. High white sugar yield was obtained at dormant seeding without irrigation delay compared to the early seeding. No significant differences were observed for white sugar yield until three and five water withholdings in 2002 and 2003, respectively. In the second year of the experiment (2003), a relatively cold winter induced about 4.5% bolters and reduced plant population with 33% compared to the early and late spring sowing treatments. In general, white sugar yield produced in response to specific irrigation amounts for dormant-seeded treatments was higher compared to early and late seeding. However, dormant seeding cannot yet be recommended as a comprehensive agricultural practice for sugar beet and, therefore, further investigations are required to improve the quality of the beet by both agronomic techniques and new improved varieties.     

Application of the CSM-CERES-Rice model for evaluation of plant density and irrigation management of transplanted rice for an irrigated semiarid environment

The objectives of this study were to evaluate the performance of the Cropping System Model (CSM)-CERES (Crop-Environment Resource Synthesis)-Rice for simulating growth and yield of rice under irrigated conditions for a semiarid environment in Pakistan and to determine the impact of plant density and irrigation regime on grain yield and economic returns. The crop simulation model was evaluated with experimental data collected in 2000 and 2001 in Faisalabad, Punjab, Pakistan. The experiment utilized a randomized complete block design with three replications and included three plant densities (one seedling hill^?1, PD₁; two seedlings hill^?1, PD₂; and three seedlings hill^?1, PD₃) and five irrigation regimes (625 mm, I₁; 775 mm, I₂; 925 mm, I₃; 1075 mm, I₄; and 1225 mm, I₅). To determine the most appropriate combination of plant densities and irrigation regimes, four plant densities from one seedling hill^?1 to four seedlings hill^?1 and 17 irrigation regimes ranging from 0 to 1600 mm, for a total of 68 different scenarios, were simulated for 35 years of historical daily weather data. The evaluation of CSM-CERES-Rice showed that the model was able to accurately simulate growth and yield of rice for irrigated semiarid conditions, with an average error of 11% between simulated and observed grain yield. The results of the biophysical analysis showed that the combination of the two seedlings hill^?1 plant density and the 1,300 mm irrigation regime produced the highest yield compared to all other scenarios. Furthermore, the economic analysis through the Mean-Gini Dominance (MGD) also showed the superiority of this treatment compared to the other treatment combinations. The mean monetary return ranged from ?47 to 1,265 $ ha^?1 among all 68 scenarios. However, to be able to furnish the demand of rice grain for local consumption and to increase export, there is a need to expand this technology among the rice growers of other rice producing areas in Pakistan through extension workers.     

滚筒式种子干燥机设计与试验

论述作物种子干燥机的特殊要求，介绍所研制的作物种子干燥机结构，分析其工作原理，确定关键参数的设计原则和方法。使用表明：该机自动化程度高，结构和参数选择合理，能满足作物种子干燥的特殊要求，具有良好干燥效果。     

Regional assessment of evaporation from agricultural irrigation reservoirs in a semiarid climate

The aim of this study was to assess the magnitude of evaporation loss from the agricultural water reservoirs (AWRs) for irrigation at a regional scale and to analyze its impact on water storage efficiency. To this end, we identified the extant AWRs for irrigation in the Segura River Basin (SRB) in southeastern Spain, and calculated the water loss from each AWR per month and year. In order to accomplish this, we determined the monthly and yearly values of the pan coefficient, K_p, taking into account the geometric dimensions (area and depth) of the AWRs and local climate conditions through a function of air vapour pressure deficit (VPD). AWR areas were identified by interpreting aerial images, while climate conditions were assessed using daily meteorological data obtained from 74 automated agro-meteorological stations located in irrigated areas. Regional evaporation losses were estimated using aggregation GIS techniques. A total of 14,145 AWRs covering 4901 ha were identified, which represents 0.26 and 1.81% of the total area of SRB and the irrigated land, respectively. Results indicated that annual water loss at a basin scale reaches 58.5 × 10⁶ m³, which corresponds to 1.404 m of water depth over the flooded area and to 8.3% of irrigation water use in the basin. This quantity is higher than the industrial demand and similar to the environmental demand, and is equivalent to 27% of the domestic water use in a region with approximately two million inhabitants. The method used, based on annual K_p, appears the most straightforward to assess regional evaporative losses from AWRs, and can be extended to other regions and climates, provided that the VPD-dependent function that gives the pan coefficient is available.     

Evapotranspiration of an hedge-pruned olive orchard in a semiarid area of NE Spain

The evapotranspiration of hedge-pruned olive orchards (Olea europaea L. cv. Arbequina) was measured under the semiarid conditions of the middle Ebro River Valley in a commercial olive orchard (57 ha) during 2004 and 2005. No measured ET_c values for this type of olive orchards have previously been reported. An eddy covariance system (krypton hygrometer KH20 and 3D sonic anemometer CSAT3, Campbell Scientific) was used. The eddy covariance measurements showed a lack of the energy balance closure (average imbalance of 26%). Then sensible and latent heat (LE) flux values were corrected using the approach proposed by Twine et al. (2000) in order to get daily measured olive evapotranspiration (ET_c) and crop coefficient (K_c) values. The highest measured monthly ET_c averages were about 3.1-3.3 mm day⁻¹, while the total seasonal ET_c during the irrigation period (March-October) was about 585 mm (in 2004) and 597 mm (in 2005). Monthly K_c values varied from about 1.0 (Winter) to 0.4-0.5 (Spring and Summer). These K_c values were similar to K_c values reported for round-shape canopy olive orchards, adjusted for ground cover, particularly during late Spring and Summer months when differences among measured and published K_c values were about less than 0.1.     

四波段作物冠层分析仪设计

为解决当前作物氮素分析成本较高、分析过程复杂、分析时间长等问题,设计了一款基于光谱学原理的四波段作物冠层分析仪,通过快速检测作物冠层植被指数预测作物长势.分析仪主要由控制单元和测量单元组成.控制单元只含一个控制器,该控制器作为整个无线传感网络的协调器,负责将各个传感器节点发送的数据进行分类、显示以及存储等,并根据测量结果计算作物营养成分含量.测量单元则由多个光学传感器组成,主要负责光学信号的采集、放大、发送等.每个传感器可以在4个光学波段进行测量,分别是绿色植物可见光主要反射峰550 nm,可见光主要吸收波段650 nm,近红外波段766、850 nm.标定试验显示光学传感器工作稳定,仪器具有较高的精度.初步玉米田间试验表明,仪器的测量结果与玉米叶片全氮含量的相关系数达到0.884.     

Seasonal water production functions and yield response factors for maize and onion in Perkerra,Kenya

Water production functions (wpf) giving the relation between crop yield and water application under furrow irrigation on a clay loam soil in the semi-arid region in Kenya (Perkerra) were derived for maize and onion. Due to deep percolation the functions were found to be curvilinear. The seasonal yield response factors K_y, giving the relationship between evapotranspiration deficit and yield depression for maize and onion for the area was computed as 1.21 and 1.28, respectively. Analytical analysis using the derived wpf for maize and existing conditions in an irrigation system located in the area confirmed that if rainfall is significant, deficit irrigation will be more attractive, and at a certain point, it is profitable to cultivate all available area.