Early Water Stress Research Articles

Effects of early water stress levels on berry set and berry development in Merlot cv. (Vitis vinifera L.)

Early water deficit at flowering results in poor berry set or aborted grape yield reduction. The main aim of this study was to find out the effects of water stress levels on berry set and embryo berry development. This study was carried out in Montpellier using by ECOTRON System, SupAgro/INRA, France. Seven years old Merlot / SO 4 grafting combination was used as a plant material. Potted grapevines were grown under natural conditions in open field. A randomized block design was used with 3 replications and each parcel had 2 grapevines and 4 water stress levels. Stress Levels were WS 0 (control) 0; -0.2 MPa, WS 1 -0.2; -0.4 MPa, WS 2 -0.4; -0.6 MPa, and WS 3 -0.6; -0.8 MPa, respectively. The stress period was started in the second week of May in the 17 th E-L stage and ended in the second week of June in 27 th E-L stage. Flower samples from clusters were collected in three days intervals and samples were examined by Technovit method. Under this early water stress conditions, the pollen viability and pollen germination ratios were not affected, but berry set ratio, phenologic stages and berry development were negatively affected. It was determined in Merlot cv. early water stress (between 19 th to 29 th stages) should be avoided especially when Ψ pd values decrease below -0.4MPa Key words : Vitis vinifera L., leaf water potential, embryo development, berry set, Merlot cv.

Using radiation thermography and thermometry to evaluate crop water stress in soybean and cotton

Abstract The use of digital infrared thermography and thermometry to investigate early crop water stress offers a producer improved management tools to avoid yield declines or to deal with variability in crop water status. This study used canopy temperature data to investigate whether an empirical crop water stress index could be used to monitor spatial and temporal crop water stress. Different irrigation treatment amounts (100%, 67%, 33%, and 0% of full replenishment of soil water to field capacity to a depth of 1.5 m) were applied by a center pivot system to soybean ( Glycine max L.) in 2004 and 2005, and to cotton ( Gossypium hirsutum L.) in 2007 and 2008. Canopy temperature data from infrared thermography were used to benchmark the relationship between an empirical crop water stress index (CWSI e ) and leaf water potential ( Ψ L ) across a block of eight treatment plots (of two replications). There was a significant negative linear correlation between midday Ψ L measurements and the CWSI e after soil water differences due to irrigation treatments were well established and during the absence of heavy rainfall. Average seasonal CWSI e values calculated for each plot from temperature measurements made by infrared thermometer thermocouples mounted on a center pivot lateral were inversely related to crop water use with r 2 values >0.89 and 0.55 for soybean and cotton, respectively. There was also a significant inverse relationship between the CWSI e and soybean yields in 2004 ( r 2 = 0.88) and 2005 ( r 2 = 0.83), and cotton in 2007 ( r 2 = 0.78). The correlations were not significant in 2008 for cotton. Contour plots of the CWSI e may be used as maps to indicate the spatial variability of within-field crop water stress. These maps may be useful for irrigation scheduling or identifying areas within a field where water stress may impact crop water use and yield.

Deficit irrigation for enhancing sustainable water use: Comparison of cotton nitrogen uptake and prediction of lint yield in a multivariate autoregressive state-space model

Deficit irrigation is an optimization strategy for achieving sustainability of irrigated crop production. A field-study of cotton (Gossypium hirsutum L.) response to a limited water supply was conducted in an Alfisol in the southern High Plains of Texas. The objectives were to investigate cotton N uptake, canopy temperature, plant spectral index and lint yield variation under deficit irrigation and to provide information for enhancing sustainability of the water resources and Alfisols in the semi-arid environment. The experimental treatments were two deficit-irrigation levels at 50% and 75% of cotton evapotranspiration (ET). Plant and soil variables were measured 15m apart along the center-pivot irrigation circles. The results show that cotton plants under the 50%-ET deficit irrigation level were 21% more water stressed (P<0.05) based on the reflectance water index ratio. The 50%-ET irrigation resulted in a 25% lint yield loss with a 33% water saving compared to the higher irrigation level (75%-ET). Plant reflectance, canopy temperature, total N uptake and lint yield were correlated with normalized difference vegetative index (NDVI), soil water content (SWC), soil NO3–N concentrations and elevation (−0.69<r<0.72, P<0.05, respectively). Future cotton lint yield is weighted on NDVI and water variation, quantified in a multivariate autoregressive state-space model. Increases in plant reflectance in the water band are signs of early plant water stress. Compared to the 12-year regional cotton lint yield obtained with full irrigation, the 75%-ET deficit irrigation would be agronomical, economical efficient in Alfisoils with only 7.8% of lint-yield loss from water stress but 25% of water saving for sustainable water use.

Re-examining the role of ABA as the primary long-distance signal produced by water-stressed roots

The role of ABA as the primary long-distance signal produced by water-stressed roots and transported to stomata continues to be challenged. We have recently reported that expression of ABA biosynthetic genes in roots only increases in the later stage of water stress. Our results support the hypothesis that in early water stress, increased levels of ABA in xylem sap are due to leaf biosynthesis and translocation to roots and from there to xylem. If so, other xylem-borne chemicals may be the primary stress signal(s) inducing ABA biosynthesis in leaves. We found that apart from ABA, sulfate was the only xylem-borne chemical that consistently showed higher concentrations from early to later water stress. We also found increased expression of a sulfate transporter gene in roots from early water stress onwards. Moreover, using bioassays we found an interactive effect of ABA and sulfate in decreasing maize transpiration rate, as compared to ABA alone. While ABA is undoubtedly the key mediator of water stress responses such as stomatal closure, it may not be the primary signal produced by roots perceiving water stress.

Photochemical reflectance index as a mean of monitoring early water stress

Water stress in plants affects a number of physiological processes such as photosynthetic rate, stomatal conductance as well as the operating efficiency of photosystem II (PSII) and non‐photochemical quenching (NPQ). Photochemical reflectance index (PRI) is reported to be sensitive to changes in xanthophyll cycle which occur during stress and could possibly be used to monitor changes in the parameters mentioned before. Therefore, the aim of this study was to evaluate the use of PRI as an early water stress indicator. Water stress treatment was imposed in a greenhouse tomato crop. CO2 assimilation, stomatal conductance, light‐adapted and dark‐adapted fluorescence as well as PRI and relative water content (RWCs%) of the rooting medium were repeatedly measured. The same measurements were also performed on well‐irrigated plants that acted as a reference. The experiment was repeated in four consecutive weeks. Results showed a strong correlation between RWCs% and photosynthetic rate, stomatal conductance, NPQ and operating efficiency of PSII but not with PRI when the whole dataset was considered. Nevertheless, more detailed analysis revealed that PRI gave a good correlation when light levels were above 700 µmol m−2 s−1. Therefore, the use of PRI as a water stress indicator cannot be independent of the ambient light conditions.

BIOCHEMICAL CHANGES IN MAIZE SEEDLINGS EXPOSED TO DROUGHT STRESS CONDITIONS AT DIFFERENT NITROGEN LEVELS

Normally, under field conditions, maize seedlings are often exposed to early water stress. The objective of the present study was to evaluate the biochemical changes in maize seedlings exposed to drought stress at different nitrogen levels. Maize (Zea mays L.) hybrid SC 704 plants were grown in 18 kg pots containing the same soil from the field that maize is naturally growing. The treatments consisted of three soil moisture regimes (A: well-watered, i.e., control; B: watered at 50% field capacity; and C: watered at 10% field capacity) and three nitrogen levels [a: 0 control; b: 60; and c: 180 kg nitrogen (N)/ha]. In a factorial experiment based on randomized complete block (RCB) design, each treatment was replicated four times. The results of this study showed that mild drought stress increased the catalase (CAT) activity, however, severe stress decreased it. Moreover, nitrogen fertilizer significantly increased CAT activity when applied at highest level. Also, drought stress significantly increased the superoxide dismutase (SOD) activity. At the mild water stress level, peroxidase (POD) activity met its peak level, however, at sever water stress its activity was suppressed and even fell below the control level. Nitrogen fertilizer significantly increased the POD activity. Also, nitrogen application significantly increased proline concentration; however, there was no significant difference between 60 and 180 kg N/ha levels. Protein concentration was increased by water stress and the highest concentration of protein was occurred at mild water stress level, however, there was not statistically any significant difference between mild and sever water stress levels. In view of biochemical traits, further research is needed on clarifications and understanding of the interactions between nitrogen requirements of maize and drought stress.

Closing the cassava yield gap: An analysis from smallholder farms in East Africa

Cassava yields in Africa are small and it remains unclear which factors most limit yields. Using a series of farm surveys and on-farm and on-station trials in Uganda and western Kenya, we evaluated the importance of abiotic, biotic and associated crop management constraints for cassava production in a range of socio-economic settings as found in smallholder farms in the region. Average yields under farmer management were 8.6 t ha −1, but these were more than doubled to 20.8 t ha −1 by using improved crop establishment, improved genotypes and 100–22–83 kg ha −1 of single-nutrient N–P–K fertilizers. A farm survey revealed large yield differences between farms. Less endowed farmers harvested less cassava per unit area than better endowed farmers (difference of 5.9 and 9.7 t ha −1 in Kenya and Uganda, respectively); differences were associated with less access to labour, poorer soils, and premature harvesting by less endowed farmers. Analysis of 99 on-farm and 6 on-station trials showed that constraints for cassava production varied strongly between sites and years. Poor soil fertility, early water stress and sub-optimal weed management limited cassava production by 6.7, 5.4 and 5.0 t ha −1, respectively, when improved crop establishment and genotypes were used. Pests and diseases were relatively unimportant, while weed management was particularly important in farmer fields during a dry year in Kenya (yield gap of 11.6 t ha −1). The use of complementary analytical tools such as multiple regression and boundary line analysis revealed that many fields were affected by multiple and interacting production constraints. These should be addressed simultaneously if significant productivity improvements are to be achieved. This will be more difficult for less endowed than for better endowed farm households, since the former lack social and financial capital to improve management.

Thermal responses of Durum wheat Triticum durum to early water stress. Consequence on leaf and flower development

Drought can alter stem apex temperature and plant phenological development and it can then have an effect on the duration of the durum wheat stages. Thermal responses of plants to water stress are tentatively analysed as regards microclimate conditions by applying three different water treatments. Apex temperature measurements showed that they are related to radiation and that acceleration of apex development could be related to their increase. To cite this article: N. Rassaa et al., C. R. Biologies 331 (2008).

Additive effects of a potentially invasive grass and water stress on the performance of seedlings of gypsum specialists

Abstract.Question: What is the combined effect of two drivers of local biodiversity changes (presence of a potentially invasive species and seasonal drought) on the performance of seedlings of plants from gypsum habitats under experimental conditions?Location: A controlled microcosm reconstruction of natural assemblages of gypsum plant communities from central Spain.Methods: We evaluated the effects of a potentially invasive grass (Lolium rigidum) and water stress on the survival, height growth and biomass of five woody species (Colutea hispanica, Gypsophila struthium, Thymus lacaitae, Lepidium subulatum and Helianthemum squamatum) from semi‐arid gypsum ecosystems. Seedlings of the five species were grown with or without the potential invader and under three watering regimes: early stress — simulating an advanced summer, late stress — simulating the characteristic timing of current summer drought and well‐watered.Results: Seedling survival and performance were negatively affected by the presence of the potential invader. Early stress had larger impacts on the gypsum species than late stress. No interactions were found between factors for any of the study variables, and responses to both factors were found to be species‐specific.Conclusions: The lack of interactions between factors indicates that the presence of the potentially invasive grass and water stress had additive effects in our study system. The negative impact of early water stress draws attention to the possible consequences of the advances of summer drought predicted for Mediterranean ecosystems. Finally, the differential responses found for the study species suggest that plant communities will not respond as a unit to global change, leading to significant changes in species composition and dominance.

Relationship between Carbon Isotope Discrimination and Grain Yield in Spring Wheat Cultivated under Different Water Regimes

Abstract In C3 plants, carbon isotope discrimination (Δ) has been proposed as an indirect selection criterion for grain yield. Reported correlations between Δ and grain yield however, differ highly according to the analyzed organ or tissue, the stage of sampling, and the environment and water regime. In a first experiment carried out in spring wheat during two consecutive seasons in the dry conditions of northwest Mexico (Ciudad Obregon, Sonora), different water treatments were applied, corresponding to the main water regimes available to spring wheat worldwide, and the relationships between Δ values of different organs and grain yield were examined. Under terminal (post‐anthesis) water stress, grain yield was positively associated with Δ in grain at maturity and in leaf at anthesis, confirming results previously obtained under Mediterranean environments. Under early (pre‐anthesis) water stress and residual moisture stress, the association between grain Δ and yield was weaker and highly depended on the quantity of water stored in the soil at sowing. No correlation was found between Δ and grain yield under optimal irrigation. The relationship between Δ and grain yield was also studied during two consecutive seasons in 20 bread wheat cultivars in the Ningxia region (Northern China), characterized by winter drought (pre‐anthesis water stress). Wheat was grown under rainfed conditions in two locations (Guyuan and Pengyang) and under irrigated conditions in another two (Yinchuan and Huinong). In Huinong, the crop was also exposed to salt stress. Highly significant positive associations were found between leaf and grain Δ and grain yields across the environments. The relationship between Δ and yield within environments highly depended on the quantity of water stored in the soil at sowing, the quantity and distribution of rainfall during the growth cycle, the presence of salt in the soil, and the occurrence of irrigation before anthesis. These two experiments confirmed the value of Δ as an indirect selection criterion for yield and a phenotyping tool under post‐anthesis water stress (including limited irrigation).

Using spectral reflectance to document water stress in bermudagrass grown on water repellent sandy soils

AbstractTo conserve natural water resources, athletic fields may be mandated to follow phase water restrictions. In order to optimize irrigation reduction, early plant responses to water stress need to be identified to avoid loss in turfgrass performance and the requirement of additional irrigation to overcome water stress. Current irrigation scheduling based on using potential evapotranspiration (ET) and water stress indices are not suitable for all growing conditions, especially in the water repellent sand soils of South Florida. This experiment was conducted to use spectral reflectance as a means to document normal and progressive water stress in ‘Tifgreen’ bermudagrass (Cynodon dactylon (L.) Pers. X Cynodon transvaalensis Burtt Davy) grown on a native water repellent sand soil. Three consecutive trials were conducted, in which bermudagrass was subjected to either no irrigation until severe visual wilt (non‐irrigated) or irrigated daily (irrigated) over a dry down period. Visual assessment of turf quality and localized dry spot occurrence verified that bermudagrass receiving daily irrigation was not water‐limited and bermudagrass receiving no irrigation was experiencing increased water stress over time. An experimentally active near‐IR/red sensor was used to monitor changes in plant architecture as a means to determine early water stress. Monitoring near‐IR/red ratios determined mid‐day depression when water demand is at the highest as well as overnight rehydration in both bermudagrasses. At the end of the dry down period, pooled trial morning near‐IR/red ratios‐afternoon near‐IR/red ratios from non‐irrigated bermudagrass was significantly greater than irrigated bermudagrass (P = 0·0035), documenting severe water stress from the non‐irrigated bermudagrass. Spectral reflectance allows real‐time, site‐specific bermudagrass water stress evaluation before it is visually identifiable. Using spectral reflectance as an early warning detection tool can be used for better irrigation decisions including pre‐emptive irrigation to avoid water stress, compared to models based on predetermined ET and water stress indices. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Photosynthesis on individual leaves of sugar beet (Beta vulgaris) during the ontogeny at variable water regimes

AbstractIt is well known that the extent of yield reduction depends not only on the severity of water stress but also on the stage of plant development. Assessing photosynthetic response of individual leaves to water deficit during the ontogeny may, therefore, offer a clue to better understand the whole plant behaviour. This research aimed at investigating the influence of early and late water stress on net photosynthesis (Pn), carbon‐isotope discrimination and other related traits on individual leaves during ontogeny. Sugar beet plants were grown in rain‐sheltered soil columns of relevant volume (300 L), subdivided into well‐watered (WW); early (S1) and late (S2) stress. In general, water stress significantly reduced leaf lifespan and Pn. Relieving the stress at about one‐third and two‐thirds of potential leaf life substantially restored Pn at the levels of WW. Stressing a previously WW leaf brought about a comparatively heavier loss than stressing a leaf since the beginning. As for leaves at different phenological times, the early leaves had higher initial photosynthetic peaks but steeper falls during their lives. An insight into the relationships between Pn and substomatal CO2 concentration (Ci) shows that in mature leaves the photosynthetic restoration following stress relief did not entail a full recovery of the electron transport rate, the parameter most severely affected by the stress. The partial reversibility of the effects of water deficiency, associated to the anticipated leaf senescence and to the natural slow‐down of net assimilation during leaf life, may be seen as a key factor in predicting to what extent the plant can tolerate drought and the damages caused by water stress.

Nitrogen dynamics and fertilizer use efficiency in leaves of different ages of sugar beet (Beta vulgaris) at variable water regimes

AbstractThe consequences of nitrogen and water stress on sugar beet yield and quality are well documented in literature, whereas their interaction has been, surprisingly, little investigated. In the present research, the influence of early and late water stress on the dynamics of N uptake in leaves of different ages and on fertilizer efficiency was studied. Sugar beet plants, grown with a 15N‐labelled fertilizer in 20 soil columns (300 L each) under a rain shelter, were subjected to three water regimes: well‐watered control (WW); early (S1) and late (S2) stress, in a completely randomized design. Periodical samplings on succeeding leaves showed a decline in nitrogen concentration with ageing, compensated for by a recovery at each new leaf. Fertilizer N was mostly taken up early in the season, as its falling contribution to total leaf nutrient shows (from 35% to 17% in 63 days). The early stress constrained the availability of fertilizer N, whose uptake was later compensated for by younger leaves, after restoration of soil moisture. At harvest, WW yielded about 20% more biomass and sugar than S1 and S2. Nitrogen concentration in stressed plants compensated for biomass losses, and the total amount of nutrient did not vary among treatments, as well as the recovery of fertilizer N (41%) and the share of plant nutrient deriving from fertilizer (16%). It is perceived that sugar beet possesses an ability to buffer the effects of water stress on nitrogen nutrition, thanks to a flexibility concerning timing and the leaves acting as sinks for either a fertilizer‐derived or soil‐derived nutrient.

Variation in pod production and abortion among chickpea cultivars under terminal drought

The effect of terminal drought on the dry matter production, seed yield and its components including pod production and pod abortion was investigated in chickpea ( Cicer arietinum L.). Two desi (with small, angular and dark brown seeds) and two kabuli (with large, rounded and light coloured seeds) chickpea cultivars differing in seed size were grown in a controlled-temperature greenhouse, and water stress was applied by withholding irrigation 1 (early podding water stress, ES), 2 (mid-podding water stress, MS) or 3 (late-podding water stress, LS) weeks after the commencement of pod set. In addition, the pod and seed growth of well-watered plants was followed for the first 19 days after pod set. Growth of the pod wall followed a sigmoid pattern and was faster in the desi than in the kabuli cultivars, while no difference was found in early seed growth among genotypes. Time of pod set affected the yield components in all treatments with the late-initiated pods being smaller, having fewer seeds per pod and smaller seeds, but no significant difference between pods initiated on the same day on the primary and secondary branches was observed. Early stress affected biomass and seed yield more severely than the later stresses, and in all stress treatments secondary branches were more affected than primary ones. Pod production was more affected by early stress than by late stress, regardless of cultivar. Pod abortion was more severe in the kabuli than in the desi cultivars, but final seed size per se did not appear to be a determinant of pod abortion under terminal drought conditions. The data indicated that the production and viability of pods was affected as soon as water deficits began to develop. The results show that pod abortion is one of the key traits impacting on seed yield in chickpeas exposed to terminal drought and that irrespective of differences in phenology, kabuli types have greater pod abortion than desi types when water deficits develop shortly after first pod set.

Effect of Water Stress at Various Growth Stages on Some Quality Characteristics of Winter Wheat

AbstractA field experiment was carried out in Erzurum (Turkey) on winter wheat to analyse the effect of water stress at different growth stages – fully irrigated (FI), rainfed (R), early water stress (EWS), late water stress (LWS) and continuous water stress (CWS), on some quality characteristics – in the 1995–96 and 1996–97 cropping seasons. Water stress had a substantial effect on most of the quality characteristics. As averages of cropping seasons, CWS, EWS, R and LWS treatments decreased grain yields by 65.5, 40.6, 30.5 and 24.0 %, respectively, compared with the FI treatment. CWS increased grain protein content by 18.1 %, sedimentation volume by 16.5 %, wet gluten content by 21.9 % and decreased 1000‐kernel weight by 7.5 g compared with FI treatment. LWS caused an increase of 8.3 % in grain protein content, 8.7 % in sedimentation volume, 10.8 % in wet gluten content and a reduction of 3.8 g in 1000‐kernel weight compared with FI. EWS and R increased sedimentation volume and wet gluten content, but decreased 1000‐kernel weight compared with FI. The effect of LWS on grain quality was more significant than that of EWS. The results suggest that soil moisture conditions increase grain yield and kernel weight of winter wheat but decrease its quality.

In-row residue management effects on seed-zone temperature, moisture and early growth of barley and canola in a cold semi-arid region in northwestern Canada

AbstractSpring crop growth is often influenced by water stress and lower soil temperature in the northern Canadian prairies. Tillage system effects on soil temperature, moisture and establishment of barley and canola in silt loam and sandy loam soils in northern British Columbia were investigated in 1992 and 1993. The tillage systems were: no-tillage (NT), modified no-tillage where surface residue was pushed aside from a 7.5cm zone above the planting rows (MNT), and conventional tillage (CT). The MNT and CT had higher weekly maximum and weekly mean seed zone temperatures than NT. Mean weekly maximum seed-zone soil temperature was 1.6°C lower in MNT and 3.7°C lower in NT than in CT during the first 10 weeks after planting (WAP) in 1992. Compared to NT and MNT, barley in CT was slow to establish during the first three WAP in the silt loam in 1992 and 1993, and in the sandy loam in 1992, due to early water stress from low rainfall. Barley emergence was delayed by 6 days in NT and 11 days in CT in 1992 and by 3 days in NT and 7 days in CT in 1993 compared to MNT in the silt loam soil. Early in the growing season, barley growth was retarded more in the CT than NT and MNT at both sites. Canola growth was significantly improved in the MNT over that in the NT and CT in 1993. The MNT was more beneficial for crop establishment during prolonged dry periods than CT, and for emergence and growth compared with NT under extremely wet soil conditions.

Mitogen-activated protein kinase signaling in postgermination arrest of development by abscisic acid.

Abscisic acid (ABA) mediates plant responses to environmental stress, particularly to water status. During germination, the embryo emerges from dormancy as the ABA concentration declines. Exposure to exogenous ABA during germination arrests development rapidly, but reversibly, enabling seedlings to withstand early water stress without loss of viability. Postgermination proteolytic degradation of the essential ABI5 transcription factor is interrupted by perception of an increase in ABA concentration, leading to ABI5 accumulation and reactivation of embryonic genes. Making use of the ABA-hypersensitive hyl1 mutant of Arabidopsis, we show that the ABA signal is transmitted to the transcriptional apparatus through mitogen-activated protein kinase signaling.

WATER STRESS DETECTION BY MONITORING FLUORESCENCE OF PLANTS UNDER AMBIENT LIGHT

Plant fluorescence is inherently weak, and it is difficult to detect and measure under broadspectrum ambient light.The relative referencing method is a technique developed to acquire a plants fluorescence signal in the presence of ambientlight. This study evaluated the methods ability to detect early signs of water stress in freestanding tomato plants as the plantswere continuously illuminated by fluorescent lamps. Water stress was initiated by imposing drought conditions, and thesubjects were tested daily over a sevenday period. Transpiration, chlorophyll content, and water status data were taken toquantify physiological changes in the plants. The relative referencing method was able to monitor early signs of water stress,but the results differed from those previously reported. The percent overshoot parameter correlated well with the early onsetof water stress, but the time to peak parameter correlated poorly. The main difference between this and the previous studywas that freestanding plants were tested, which affected the amount of incident light on the leaves during testing. In addition,younger plants were used, which had an effect on the fluorescence response. In spite of these differences, the results showedthat the relative referencing method was able to detect early signs of water stress in freestanding tomato plants.

Use of sub-hourly soil water content measured with a frequency-domain reflectometer to schedule irrigation of cabbages

Laboratory and field measurements of soil water content were obtained using gravimetric and Theta-Probe methods, the latter a frequency-domain reflectometry method. We obtained real-time in situ measurements of soil water content at depths of 30, 80, 160, 240 and 350 mm to evaluate irrigation practice. A datalogger recording the change in soil water content (and cumulative irrigation) at 20-min intervals was used, with appropriate calculations and graphical presentation, to predict the time and amount of irrigation water required for soil water content to reach field capacity. Measurements at three instead of five depths yielded a different depth-averaged soil water content under relatively dry conditions (less than 0.273 m3 m−3), and predicted a later start for irrigation and early crop water stress. Investing in additional sensores for scheduling irrigation would be compensated by financial resources saved through avoiding excess or deficit irrigation, and the associated application cost, loss of nutrients and soil due to deep percolation and erosion, and loss of crop production.

Model of crop:weed competition applied to maize:Abutilon theophrasti interactions. II. Assessing the impact of climate: implications for economic thresholds

The practical application of single‐season economic thresholds for post‐emergence weed control decisions has been frustrated by the impact of growing season, climate and edaphic factors on crop:weed interactions. Competition in a mixed plant community is a dynamic process that is contingent upon species‐specific growth characteristics and their expression based on environmental conditions. To address these issues, a modified version of the ALMANAC competition model was parameterized and run to simulate maize:Abutilon theophrasti competition with 30 years (1966–95) of historical climate data for a site in New York State. Simulations indicate that, when weeds do not emerge before maize, maize will only suffer substantial yield reductions from A. theophrasti competition in two out of every 10 years at this site. It is also evident that economic thresholds based solely on the level of weed infestation are inherently flawed. Long‐term simulation results suggest that estimates of early season water stress could be used as an independent tool for rationalizing post‐emergence control decisions. Shifting the focus from quantifying the infestation intensity of the weed population to assessing the competitive status of the maize crop indirectly with climate information may alleviate many of the problems commonly associated with threshold management strategies.