Spring Irrigation Research Articles

Planting and Irrigation Methods for Cotton in Southern Xinjiang, China

AbstractIn order to provide a scientific technology reference for cotton planting and management in southern Xinjiang that is based on practical investigations and existing achievements, cotton planting and irrigation methods were divided into four groups. In addition, the applications of these methods are discussed. The four types of cotton‐planting methods are as follows: (i) one film + no pipes + four rows; (ii) one film + single pipe + four rows; (iii) one film + double pipes + four rows; and (iv) double films + double pipes + four rows. The four types of cotton field irrigation methods are as follows: (i) winter irrigation (spring irrigation) + routine flooding irrigation; (ii) winter irrigation (spring irrigation) + drip irrigation under mulch; (iii) seeding after drip irrigation + drip irrigation under mulch; and (iv) dry seeding before drip irrigation + drip irrigation under mulch. The planting and irrigation methods for cotton supplement each other and are coupled based on local climate, soil, surface water and groundwater conditions. In addition, the most scientifically reasonable, cost‐effective, water‐saving and productive methods must be selected. Copyright © 2016 John Wiley & Sons, Ltd.

Impact of saline water irrigation on water use efficiency and soil salt accumulation for spring maize in arid regions of China

Saline water irrigation represents the future of agriculture in the arid regions of northwestern China. Therefore, saline water irrigation experiments for spring maize were performed for 3 years from 2009 to 2011 in arid regions of northwestern China, and the impact of irrigation with saline water at different concentrations on the water use efficiency and soil salt accumulation was investigated. A SWAP model was calibrated and verified using field experiment data. The relationships of the salt concentration of the irrigation water with the yield and water use efficiency of spring maize were simulated using the SWAP model. Furthermore, the salt transport across the soil layers was quantitatively analyzed. The results showed the following: (1) irrigation with water containing low concentrations of saline (<3g/L) for 3 consecutive years combined with a single application of fresh spring water before sowing every year did not cause significant changes in the yield of spring maize. (2) Saline water irrigation for 3 consecutive years resulted in an increase in the salt accumulation at a soil depth of 0–100cm in 2011. This finding indicated that spring irrigation did not completely leach the salt introduced by saline water irrigation. (3) The SWAP simulation indicated that the yield of spring maize declined by 622kg/ha for every 1g/L increase in the salt concentration. When the salt concentration of the irrigation water was less than 3g/L, the yield of the spring maize was reduced by less than 10%, whereas salt concentrations above 3g/L decreased the yield much more significantly. A simulation over 10 consecutive years of saline water irrigation showed that the spring maize yields of T3, T6 and T9 will reduce by 8%, 33% and 52%, respectively, compared with the yield in 2009. (4) Despite the differences in the salt concentration of irrigation water, the salt residue in the 0–100cm soil layer due to irrigation with 3g/L, 6g/L and 9g/L saline water accounted for approximately 60% of the total salt in the irrigation water in 2011. The remaining 40% of the salt leached to the soil layer below 100cm. In conclusion, irrigation with saline water at concentrations below 3g/L will reduce the yield by no more than 10% compared with fresh water irrigation, but long-term saline water irrigation will result in significant yield losses, even for low concentrations of salt. Thus, the accumulation of salt in the soil after many years of saline water irrigation needs to be addressed by using a proper irrigation schedule in order to ensure the sustainability of saline water irrigation.

Relationships of climate and irrigation factors with malaria parasite incidences in two climatically dissimilar regions in India

We examine how climate and irrigation conditions are associated with malaria infection from 1986 to 1995 in two climatically dissimilar regions in India. We analyze annually averaged malaria parasite incidence (API) and seasonally averaged climate and irrigation variables in western Rajasthan and Arunachal Pradesh. In arid western Rajasthan, API is significantly positively correlated with summer precipitation and soil moisture, and negatively correlated with summer potential evapotranspiration. Irrigation variables during boreal spring show a significant positive correlation with API in the moisture-limited region. In humid Arunachal Pradesh, API is positively related to summer temperature, but negatively related to summer precipitation and spring irrigation variables, while no statistically significant correlations are observed. During the years of high sea surface temperatures (SSTs) in the tropical western Pacific, increasing precipitation (accompanied by decreasing temperature) in northwestern India appears to promote malaria infection in arid western Rajasthan. However, during the same years, decreasing precipitation and increasing temperature result in increasing malaria incidence in humid Arunachal Pradesh. The statistically significant relationships of climate and irrigation factors with API in western Rajasthan suggest that increasing spring irrigation activity and wetter summer climates related to warmer SST in tropical western Pacific could increase malaria risk in the arid climate region.

Irrigation scheduling and winter wheat grain yield estimation under precipitation uncertainty – A case study in Badjgah area (Fars Province, Iran)

Addressing deficit irrigation scheduling (DIS) for strategic crop production (especially wheat) under precipitation uncertainty is a priority for irrigation scheduling in drought conditions. This research investigated the precipitation uncertainty by enacting optimistic and pessimistic scenarios for the next 20 years by considering the statistical record of climate in Badjgah area. DIS was conducted in spring in two ways: (1) reducing the quantity of irrigation water at each irrigation event; (2) reducing the number of full irrigation events. Results indicated that, owing to the effect of precipitation increase on yield enhancement, grain yield in the optimistic scenario was on average 7% higher than those obtained in the pessimistic scenario. Furthermore, grain yields obtained via the second method of DIS was on average 8% higher than those obtained by the first method of DIS and further by increasing the water reduction fraction (WRF) to 0.6, this difference reached about 20% due to the effect of early spring irrigation events on yield enhancement. At low irrigation application efficiency (Ea), the difference between DIS methods was greater at higher WRF. Net income obtained through the second method of DIS was on average 70% higher than those obtained via the first method of irrigation for all conditions due to decreasing the number of irrigation events and thus decreasing the production costs. Eventually, results indicated that in both scenarios of the precipitation uncertainty in drought conditions, the second method of DIS, i. e., application of available water based on growth stage, was more fruitful.

Irrigation frequency and seasonal timing effects on perennial ryegrass (Lolium perenne L.) seed production

Limited information is available on frequency and seasonal timing of irrigation in perennial ryegrass seed crops. Two field experiments were conducted in Oregon to investigate irrigation effects on seed production in seven cultivars of perennial ryegrass. Three spring irrigation treatments were tested in Experiment 1 over a two-year period: none (control), single irrigation to fill the soil profile to field capacity (FC) at anthesis, and multiple irrigations to maintain soil water deficit ≤50mm below FC until the beginning of seed fill; and single fall and spring irrigation timings were tested in Experiment 2 over a three-year period. Spring irrigation increased seed yield of perennial ryegrass in both experiments while fall irrigation had no effect in the second experiment. A single spring irrigation increased seed yield by an average 16.1% whereas multiple irrigations resulted in an average increased yield of 24.6% in Experiment 1. Single spring irrigation in Experiment 2 increased seed yield by an average 6.5%. Seed yield increases attributable to spring irrigation were the result of a combination of increased seed number and seed weight. Spring irrigation increased harvest index and seed set. Water use efficiency was reduced by spring and fall irrigation. Perennial ryegrass seed crops can benefit from spring irrigation but the frequency of irrigation is best determined by the quantity of water available and economic considerations.

What functional strategies drive drought survival and recovery of perennial species from upland grassland?

Extreme climatic events such as severe droughts are expected to increase with climate change and to limit grassland perennity. The present study aimed to characterize the adaptive responses by which temperate herbaceous grassland species resist, survive and recover from a severe drought and to explore the relationships between plant resource use and drought resistance strategies. Monocultures of six native perennial species from upland grasslands and one Mediterranean drought-resistant cultivar were compared under semi-controlled and non-limiting rooting depth conditions. Above- and below-ground traits were measured under irrigation in spring and during drought in summer (50 d of withholding water) in order to characterize resource use and drought resistance strategies. Plants were then rehydrated and assessed for survival (after 15 d) and recovery (after 1 year). Dehydration avoidance through water uptake was associated with species that had deep roots (>1·2 m) and high root mass (>4 kg m(-3)). Cell membrane stability ensuring dehydration tolerance of roots and meristems was positively correlated with fructan content and negatively correlated with sucrose content. Species that survived and recovered best combined high resource acquisition in spring (leaf elongation rate >9 mm d(-1) and rooting depth >1·2 m) with both high dehydration avoidance and tolerance strategies. Most of the native forage species, dominant in upland grassland, were able to survive and recover from extreme drought, but with various time lags. Overall the results suggest that the wide range of interspecific functional strategies for coping with drought may enhance the resilience of upland grassland plant communities under extreme drought events.

Sprinkler irrigation uniformity and crop water productivity of barley in arid region

An investigation has been organized To study the effect of the sprinkler irrigation system design on irrigation uniformity and its impact on barley crop yield and crop water productivity (CWP). The spring irrigation operating pressures (P) were 200 kPa (P1), 250 kPa (P2) and 300 kPa (P3). The sprinkler riser heights were 100 cm (H1), 125 cm (H2) and 150 cm (H3) from the ground. The results demonstrated that the maximum values of coefficient of uniformity (CU) and distribution uniformity (DU) (91.37 % and 0.85, respectively) were obtained at P3H3, while the minimum values (78.21 % and 0.71, respectively) were obtained at P1H1.Under P3H3 treatment, the highest values of 5.50 t ha-1 and 63.49 cm of grain yield (GY) and barely plant height (PH), respectively were recorded. The highest CWP value (0.75 kg m-3) was obtained when the P3H3 treatment was applied, while the lowest yield (0.36 kg m-3) was recorded under P1H1 treatment. According to the results of this experiment, under Sebha environmental conditions and similar regions, it is recommended to operate the solid set sprinkler irrigation system at P3H3 to obtain the highest CU and DU and consequently the highest GY, PH and CWP.

Earth surface deformation in the North China Plain detected by joint analysis of GRACE and GPS data.

Mass redistribution of the Earth causes variable loading that deforms the solid Earth. While most recent studies using geodetic techniques focus on regions (such as the Amazon basin and the Nepal Himalayas) with large seasonal deformation amplitudes on the order of 1–4 cm due to hydrologic loading, few such studies have been conducted on the regions where the seasonal deformation amplitude is half as large. Here, we use joint GPS and GRACE data to investigate the vertical deformation due to hydrologic loading in the North China Plain, where significant groundwater depletion has been reported. We found that the GPS- and GRACE-derived secular trends and seasonal signals are in good agreement, with an uplift magnitude of 1–2 mm/year and a correlation of 85.0%–98.5%, respectively. This uplift rate is consistent with groundwater depletion rate estimated from GRACE data and in-situ groundwater measurements from earlier report studies; whereas the seasonal hydrologic variation reflects human behavior of groundwater pumping for agriculture irrigation in spring, leading to less water storage in summer than that in the winter season. However, less than 20% of weighted root-mean-squared (WRMS) reductions were detected for all the selected GPS stations when GRACE-derived seasonal deformations were removed from detrended GPS height time series. This discrepancy is probably because the GRACE-derived seasonal signals are large-scale, while the GPS-derived signals are local point measurements.

No need for further fruit thinning in water-deprived loquat trees at preharvest

Preharvest deficit irrigation (DI) during fruit growth may reduce fruit size in ‘Algerie’ loquat (Eriobotrya japonica Lindl.), but it can eventually enhance other parameters of fruit quality and earliness, making this crop more profitable. With the aim to determine the optimum level of fruit load per panicle under preharvest DI, we have compared harvest date, fruit size, yield, and revenue from ‘Algerie’ loquat trees analysing four different fruit loads under two irrigation treatments: T1, a control in which the trees’ water requirements were fully satisfied from bloom to harvest; and T2 (a treatment of preharvest DI) in which irrigation was withheld from stage II of fruit development until the end of harvest (a total of 13 and 14 weeks, depending on the season). The four levels of fruit load were 1, 2, 3 and 4 fruits per panicle. The results showed the absence of significant interactions between irrigation and fruit load treatments, probably due to the low levels of water stress reached during preharvest. DI did not enhance fruit maturity substantially and therefore failed to advance the harvest date. Pack out was slightly improved by heavier fruit thinning treatments; however, that improvement did not compensate the important yield loss caused by the reduction in the number of fruit per panicle. Therefore, a crop load of 4 fruits per panicle provided the highest revenue in both irrigation treatments. An average water saving of 2281m3/ha (33% of the water applied in T1) was achieved by preharvest DI. In conclusion, the low levels of water stress reached by withholding irrigation in spring in SE Spain do not impose heavier fruit thinning in ‘Algerie’ loquats.

A Modeling Study of Irrigation Effects on Surface Fluxes and Land–Air–Cloud Interactions in the Southern Great Plains

AbstractIn this study, the authors incorporate an operational-like irrigation scheme into the Noah land surface model as part of the Weather Research and Forecasting Model (WRF). A series of simulations, with and without irrigation, is conducted over the Southern Great Plains (SGP) for an extremely dry (2006) and wet (2007) year. The results show that including irrigation reduces model bias in soil moisture and surface latent heat (LH) and sensible heat (SH) fluxes, especially during a dry year. Irrigation adds additional water to the surface, leading to changes in the planetary boundary layer. The increase in soil moisture leads to increases in the surface evapotranspiration and near-surface specific humidity but decreases in the SH and surface temperature. Those changes are local and occur during daytime. There is an irrigation-induced decrease in both the lifting condensation level (ZLCL) and mixed-layer depth. The decrease in ZLCL is larger than the decrease in mixed-layer depth, suggesting an increasing probability of shallow clouds. The simulated changes in precipitation induced by irrigation are highly variable in space, and the average precipitation over the SGP region only slightly increases. A high correlation is found among soil moisture, SH, and ZLCL. Larger values of soil moisture in the irrigated simulation due to irrigation in late spring and summer persist into the early fall, suggesting that irrigation-induced soil memory could last a few weeks to months. The results demonstrate the importance of irrigation parameterization for climate studies and improve the process-level understanding on the role of human activity in modulating land–air–cloud interactions.

Spring irrigation of tall fescue for seed production

No information is available on irrigation management in tall fescue [Schedonorus phoenix (Scop.) Holub] seed crops. The objective of this study was to investigate spring irrigation effects on six cultivars of tall fescue managed for seed production. Field trials were conducted with three irrigation treatments: none (control), single irrigation to fill the soil profile to field capacity at anthesis, and multiple irrigations to maintain soil water deficit ≤50mm below field capacity until the beginning of seed fill. Wet conditions in Year 1 prevented multiple irrigations, so only the single (78mm) application was made. Dry conditions in Year 2 were conducive to both single (112mm) and multiple (172mm) treatments. Crop responses to single irrigation were the same as multiple irrigations. Fertile tiller number, spikeletspanicle−1, and floretsspikelet−1 were not affected by irrigation treatments. Irrigation×cultivar interactions for seed yield were evident in both years. Yield increases varied among cultivars and irrigation treatment, ranging from 15% to 47% in Year 1. In Year 2, seed yield in ‘Velocity’ was not affected by irrigation but was increased by 14% across other cultivars. Seed number and weight were independently influenced by irrigation and cultivar. Irrigation consistently increased seed weight, but increased seed number only in Year 1 which led to the greatest seed yield increases observed. There was no effect of irrigation on HI but WUE was influenced by irrigation×cultivar interactions. Tall fescue seed yield can be increased by strategically timed spring irrigation but the response is dependent on year and cultivar.

Effects of irrigation on precipitation in the arid regions of Xinjiang, China

Soil moisture is an important parameter for the interaction between soil and atmosphere. It is the sec- ond important factor that influences climate change, next to sea surface temperature (SST). Most previous studies focused on the monsoon regions in East China, and only a few laid emphases on arid environments. In Xinjiang, which is located in Northwest China, the climate is typically arid and semi-arid. During the past 20 years, the pre- cipitation in Xinjiang has shown a significant increasing trend, and it is closely related to oasis irrigation. This paper aims at discussing whether abnormal soil moisture in spring can be the signal to forecast summer precipitation. The effects of abnormal soil moisture due to farm irrigation in spring in arid environments on regional climate are inves- tigated by using a regional climate model (RegCM3). The results indicate that positive soil moisture anomaly in irrigated cropland surface in May led to an increase in precipitation in spring as well as across the whole summer. The impact could last for about four months. The effects of soil moisture on the surface air temperature showed a time-lagging trend. The summer air temperature declined by a maximum amplitude of 0.8oC. The increased soil moisture could enhance evaporation and ascending motion in the low troposphere, which brought in more precipi- tation. The soil moisture affected regional weather and climate mainly by altering the surface sensible and latent heat fluxes.

Yield and water use response of winter wheat to winter irrigation in the North China Plain

With intensifying water shortage, adoption of deficit irrigation strategies is likely to increase around the world. Winter wheat (<i>Triticum aestivum</i> L.) is one of the crops that has successfully been grown with deficit irrigation in the North China Plain. However, irrigating once before winter wheat enters dormancy (simplified as winter irrigation [WI]) is still a popular practice in this region. This study investigated the necessity of this irrigation and its effects on crop performance to provide guidelines for better irrigation management. Field experiments at two sites with up to five irrigation treatments (from rainfed up to three irrigations with or without WI) in a randomized block design with four replications were conducted for two to three winter wheat growing seasons from 2006 to 2009 in the North China Plain. Results showed that with good soil moisture at sowing, winter wheat achieved its maximum grain production with two irrigation applications in dry seasons and one irrigation application in wet seasons, both without WI. Winter irrigation increased evapotranspiration by 20 to 25 mm (0.79 to 0.98 in) and increased drainage from the root zone profile by 20 mm during the long winter dormancy period. With good soil moisture conditions at sowing plus some rainfall, soil moisture before winter wheat enters dormancy would be adequate so WI would have little effect on crop growth. Otherwise, the moisture for the top 50 cm (19.69 in) soil profile might become too dry, which would have a negative affect on winter wheat growth at the recovery stage without WI. However, even under dry conditions, WI didn9t increase yield of winter wheat with a postdormancy irrigation in early spring. With the same number of irrigation applications, the ones with WI produced lower water-use efficiency (WUE) values than the ones without WI. Under limited irrigation application, irrigation in early spring after winter dormancy produced greater yield and WUE than that with WI. Applying WI encouraged root growth at the topsoil profile, while withholding WI enhanced root length density in the deep soil layer. The results showed that WI increased evapotranspiration and drainage and reduced WUE. Thus, WI should be replaced by early or late spring irrigation after winter dormancy depending on soil moisture conditions.

Rice striped stem borer, Chilo suppressalis (Lepidoptera: Pyralidae), overwintering in super rice and its control using cultivation techniques

Super rice has the potential to deliver very high yields but is also susceptible to attack by the striped rice stem borer, Chilo suppressalis. In this study, surveys and field trials were performed to examine this problem and efficient ways were found to lower the borer’s population density. It was found that larger super rice plants provided more refuges for borers to evade insecticide contact and had a longer growth period allowing borers to complete their larval development in an intact environment. The current cultivation regime was shown to favour outbreaks of borers. Super rice is harvested leaving tall field stubbles until the following growing season, thus providing food and cover in which borers may successfully overwinter. We found that borer larvae were distributed to a greater height in the plants of super rice than in common rice, making control through agricultural operations more feasible. Burning fields after harvest, which killed 84.5% of borers, seemed the best remedy, though this practice is forbidden in China for ecological reasons. Leaving short stubbles followed by appropriate treatment of the rice straw killed 74.0% of the borer population. In addition, spring irrigation after the pre-pupation dispersal movements of borers killed more than half of the overwintering population. Pre-winter rotary tillage had little effect on borer numbers but enhanced the population reduction effect of irrigation the following spring. Based on the results obtained, efficient control of borers on super rice can be achieved by harvesting leaving short stubbles, followed by rotary tillage and spring irrigation. This regime can reduce the borer population by more than 98%, minimising chemical use and maximising use of a reduced agricultural workforce.

Exploring six reduced irrigation options under water shortage for ‘Golden Smoothee’ apple: Responses of yield components over three years

Abstract Water for irrigation is in short supply worldwide, therefore reduced irrigation options will have to be explored. We did this for ‘Golden Smoothee’ apple over the growing seasons of 2003–2005 at the IRTA-Estacio Experimental de Lleida (41°37′ N; 0° 52′ E; 260 m a.s.l.), Catalonia, Spain. This region has a temperate climate with winter-dominant rainfall. Averages of annual rainfall and reference evapotranspiration over 2000–2009 were, respectively, 371 and 1023 mm. The treatments were: Control (C), receiving full irrigation; spring irrigation (SI), where at the budbreak 80 mm of water was applied followed by watering so that the total water applied in the season was either at 33% of C (SI-33) or at 50% of C (SI-50); and deficit irrigation (DI), where trees were irrigated either with 33% of C (DI-33) or with 50% of C (DI-50). Water in DI was applied either through one dripper per tree (DI-33-1d and DI-50-1d) or through two drippers per tree (DI-33-2d and DI-50-2d). Trees showed biennial bearing with 2004 being an ‘off-year’ when treatment effects on yield were largely masked by the higher values of stem water potential associated with lower crop loads. SI-50 and SI-33 performed poorly and cannot be recommended. For each of the DI treatments, the one-dripper version increased fresh market yield and fruit size. For example, although DI-50 performed better than DI-33, DI-33-1d was similar in performance to DI-50-2d. Under water shortage, we recommend whole-season application of DI-50-1d and DI-33-1d depending on the availability of water supply.

Dunhuang Gazetteers of the Tang Period

AbstractThe collection of Dunhuang manuscripts discovered in the beginning of the twentieth century contains several gazetteers about the Dunhuang region itself. During the Han to late Tang dynasty, the period covered by these gazetteers, Dunhuang was a western frontier consisting mainly of a few remote oases surrounded by expansive desert. Our analysis of the geographical and historical descriptions found in these rare fragments reveals that the overabundance of water once seriously threatened the livelihood of its residents while the availability of drinkable spring water and irrigation projects may have led to the prosperity of the region. This prosperity was manifested by active commerce with Central Asia through the Silk Road and the establishment of courier stations. These gazetteers are important because they supplement the accepted standard histories with more accurate accounts of historical events than previously available. Of particular interest is a one-sheet fragment that is likely the earlies...

Storage Efficiency of Off‐Season Irrigation

Water levels in the Ogallala aquifer are declining, and with the resultant decrease in water capacity of wells, irrigators face difficulty in meeting crop water needs. Off‐season irrigation is common in the region, although research has shown it is often inefficient. Storage efficiency of off‐season irrigation is affected primarily by the amount of water in the soil profile during storage. Because of much interest in off‐season irrigation, our objective was to describe the relationship between water storage efficiency and soil profile water content. Through use of simulation results from a water balance model, we calculated net water gain on 15 May that resulted from fall or spring irrigation. Storage efficiency was related with the maximum of soil water (SW) from irrigation to 15 May. Storage efficiency was 90 to 95% of spring, or 80 to 85% of fall net irrigation amount, with SW in the lower half of the available water (AW) zone. As SW increased above ≈55% AW for fall or ≈60% AW for spring irrigation, storage efficiency decreased and approached zero with SW near 100% AW. This analysis will help producers understand water storage efficiency of off‐season irrigation and how storage varies with SW.

Economic evaluation for Alfalfa Farms under spring irrigation system

Hence this study directed to evaluate Alfalfa farm irrigated by Springer irrigation system, which located in western desert, north Eufraties river away from its stream about 6 k.m. Technical and economical criteria have been got via on going work of this farm ,it point out that this farm has sound contribution to preserve water comparing with same area planted with same crop irrigated in traditional water flow irrigation system, it is fund that annually consumption water for sprinkler system about 5000 m3/ Donam less than the other way which consumpt about 8690 m3/ Donam. The production of each m3 for the farmer is about 2.1 k.g. of dried Alfalfa to the price of 320 I.D. More that its counter part of wheat, which is 6 k.g. per m3 its price about 240 I. D. Economically the economic criteria point out the positive ness of this farm performance, when the addative value reaches to total of 399 Million I.D. annually and the pure addative value of about 355 Million I.D., it is found that the invester can regain his capital in about 4.6 year and he obtained aprofit of about 204.8 Million I.D. and the invested Dinar achieved about 25% profit in average.

Accumulation and Profile Distribution of Soil Mineralized Nitrogen in Fallow Season

Two long‐term field experiments were conducted in the Shenyang Ecological Experimental Station, aimed to study accumulation and profile distribution of soil mineralized nitrogen (N) in upland and paddy fields with different fertilization treatments in the fallow season. Results showed that normal fertilizer application could result in accumulation and leaching loss of mineralized nitrogen (N) in the deeper layer of the soil profile in the nongrowing season in monoharvesting farmland. Accumulation of mineralized N reached the highest in the 1‐m soil profile before freezing. Compared with the upland field, the accumulation amount of inorganic N in the 1‐m paddy soil profile with different fertilization treatment was significantly lower. The loss profile of nitrate (NO3 −)‐N is observed before and after the first irrigation in spring; the first irrigation before transplanting rice seedlings in spring can cause soil nitrate leaching. Fertilization could obviously increase the accumulation and loss of NO3 −‐N in upland and paddy fields in the fallow season, which creates the potential for groundwater nitrate pollution.

Effects of Water Deficit and Supplemental Irrigation on Winter Wheat Growth, Grain Yield and Quality, Nutrient Uptake, and Residual Mineral Nitrogen in Soil

Water deficit (WD) is a primary factor that limits winter wheat (Triticum aestivum L.) production in the Loess Plateau of China, as rainfall during the growing season is usually low and erratic in this region. Supplemental irrigation (SI) in early winter and/or early spring has been widely practiced to mitigate this problem. However, the timing at which WD and SI occur can influence grain yield and quality. A simulation pot experiment was conducted from October 1999 to June 2000 to determine the effects of WD and SI applied at different stages on winter wheat growth, grain yield and quality, nutrient uptake, and residual mineral nitrogen (N) in soil. The results showed that wheat at tillering, stem elongation, and grain‐filling growth stages was more sensitive to WD than at dormant stage. Water deficit at stem elongation or grain‐filling stage not only decreased biomass, but it also appeared to have inhibited the translocation of assimilates from the vegetative plant parts to the heads, especially when WD occurred during grain‐filling stage. Water deficit at dormant stage had no significant effect on biomass production, but it may have hindered the allocation of assimilates to the heads. Water deficit at tillering tended to increase grain harvest index but decreased biomass. Grain yield was significantly decreased (15–91%) by WD at all four growth stages. Translocation of N, phosphorus (P), and potassium (K) also appeared to have been pronouncedly impeded by WD. This inhibitory effect was more apparent at the advanced growth stages of winter wheat. Supplemental irrigation applied at dormant or grain‐filling stage increased grain yield (12% and 35%, respectively). Of the nutrients uptake, only N uptake in grain was increased (21%) when SI occurred at grain‐filling stage. Application of SI at tillering stage significantly decreased grain yield and N and P uptake in the grain, possibly due to decreased biomass and nutrient uptake in the whole plant. Supplemental irrigation at elongation stage increased biomass and N, P, and K uptake in the whole plant, but it appeared to have decreased translocation of assimilates and nutrients to the heads. Supplemental irrigation decreased or had no effect on N, P, and K concentration in grain. The main form of residual mineral N in soil was nitrate‐N, and it was markedly increased when WD was applied at all growth stages or when SI was applied at tillering stage. Supplemental irrigation at elongation or grain‐filling stage significantly decreased residual soil nitrate‐N.