Critical Growth Stages Research Articles

Long-term tillage and irrigation management practices: Strategies to enhance crop and water productivity under rice-wheat rotation of Indian mid-Himalayan Region

Since reckonable understanding of yield response under long-term (16 year) conservation management practices is the key to improve the productivity and physico-chemical indicators of rice-wheat rotation, impact of long-term tillage and irrigation levels on productivity, yield trend, soil organic carbon (SOC) fractions, carbon pools and sequestration under rice-wheat rotation on sandy clay loam soil of the mid-Himalaya were quantified. A field experiment started from 2001 through 2016 to assess the effect of tillage alterations conventional tillage (CT) and zero tillage (ZT) and four irrigation levels I1: pre-sowing (PS), I2: PS + crown root initiation (CRI), I3: PS + CRI + panicle initiation (PI)/flowering (FL), and I4: PS + CRI + PI/FL + grain filling (GF), applied at the critical growth stages to rice-wheat rotation. Results confirmed that irrigation management had a significant (p = 0.001) positive impact on grain yield of rice, wheat and system yield after 16 year continuous cropping.We also recoded that, plot with four irrigation (I4) had ∼ 28, 40 and 35 % higher grain yield of rice, wheat as compared to single irrigation or I1 (2.04, 2.99 and 5.05 Mg ha−1), respectively. Rice yield declined significantly (r = 0.68; p = 0.003) by 70 kg ha−1 year−1 under ZT plots than CT plots (52 kg ha−1 year−1). Decreasing trend of rice yield ranged from 42 kg ha−1 year-1 in four irrigations (I4) to 75 kg ha−1 year−1 single irrigation (I1). Whereas, wheat yield increased (58 kg ha−1 year−1) non-significantly over the years under ZT plots whereas under CT plots (-13.6 kg ha−1 year−1) it had declining trend with time. Unlike rice yield, impact of irrigation on wheat yield had positive trends or increasing trends with time. Plots under long-term ZT along with irrigation practice significantly increased total porosity and decreased pH and bulk density (BD) mainly in surface layer. Different pools of SOC were also significantly increased under ZT as compared to CT only in surface layer (0−15 cm).We conclude that, ZT system increased yield of wheat and diminished rice yield after 16 years of experimentation. But apart from yield, ZT also improved physico-chemical indicators of soil and enhanced carbon sequestration. The WUE of rice and wheat (4.20 and 11.0 kg ha−1 mm−1) had slightly higher under ZT as compared to CT. It is suggested that ZT is more desirable for efficient water utilization in such conditions. Frequent irrigation (I4) was more desirable for maintaining optimum moisture condition for sustainable crop production.

Efficient Control of Apple Scab with Targeted Spray Applications

For two consecutive growing seasons (2017 and 2018), three different fungicide spray programs, each with five sprays from unrelated chemical groups, were evaluated for their effectiveness against apple scab (causal agent: Venturia inaequalis) in an experimental trial in Greece. The targeted application programs consisted of five sprays with protective and systemic fungicides from unrelated chemical groups, in alternation. The applications were started at the pink bud stage (a copper-based fungicide had previously been applied at the green bud stage) and completed at the second fruit fall to arrest the primary infections by ascospores. These five-spray programs were compared to the standard farmer practice (12 sprays per season), whereas untreated plots were used as controls. The timing of the applications was based: a) on the critical growth stage of the crop, and b) on the risk analysis for infection calculated by the software Field Climate, which incorporated meteorological data from the trial site. All the five-spray programs were of very high efficacy against apple scab, showing disease severity ratings on leaves and fruits below 1.88%. In both years, in the untreated control, the disease incidence and severity on leaves ranged from 96.5% to 99.3% and from 65.2% to 75.93%, respectively. The five-spray programs showed similar efficacy to the standard 12-application program in all cases. From the results, it becomes apparent that apple scab can be controlled effectively by five targeted applications with selected fungicides at critical growth stages of the crop.

Impact of no-till, cover crop, and irrigation on Cotton yield

Water is the limiting factor for crop production within the southern US Great Plains and it has become a critical resource for multiple stakeholders. Hence, efficient irrigation and cropping systems are of paramount importance to conserve water resources. The objective of this study was to determine the effect of irrigation timing and quantity, cover crop use and tillage on cotton production in an established conservation tillage system. Evaluated tillage systems included: 1) conventional tillage (CT); 2) strip-tillage (ST); 3) no-till (NT); and 4) NT with a terminated wheat cover crop (NT-W). Irrigation treatments included 1) 5.08-6.35 mm d−1 initiated mid-season (LOW); 2) 6.35-8.38 mm d−1 initiated mid-season (MED); and 3) 5.08-6.35 mm d−1 initiated early-season (HIGH). No significant differences in lint yield or irrigation water use efficiency (IWUE) were observed between MED and HIGH. Although HIGH resulted in 12 % greater lint yields than LOW, HIGH resulted in 67 % greater irrigation water applications. LOW resulted in significantly greater IWUE than MED and HIGH. No-till systems, with and without a cover crop, had significantly greater lint yields and IWUE than CT. Furthermore, inclusion of wheat in NT increased yields and IWUE compared with ST. Applying irrigation water at a critical growth stage proved to be more water efficient than early season irrigation that was used to bank moisture in the soil profile. Delaying irrigation application until critical growth stages and using cover crops should be considered as best management approaches to conserve water resources while sustaining cotton production in the Southern Great Plains.

Changes in the Phenotype of Winter Wheat Varieties Released Between 1920 and 2016 in Response to In-Furrow Fertilizer: Biomass Allocation, Yield, and Grain Protein Concentration.

Plant breeding has increased the yield of winter wheat (Triticum aestivum L.) over decades, and the rate of genetic gain has been faster under high fertility in some countries. However, this response is not universal, and limited information exists on the physiological traits underlying the interaction between varieties and fertilization. Thus, our objectives were to identify the key shifts in crop phenotype in response to selection for yield and quality, and to determine whether historical and modern winter wheat varieties respond differently to in-furrow fertilizer. Factorial field experiments combined eight winter wheat varieties released between 1920 and 2016, and two fertilizer practices [control versus 112 kg ha-1 in-furrow 12 -40-0-10-1 (N-P-K-S-Zn)] in four Kansas environments. Grain yield and grain N-removal increased nonlinearly with year of release, with greater increases between 1966 and 2000. In-furrow fertilizer increased yield by ~300 kg ha-1 with no variety × fertility interaction. Grain protein concentration related negatively to yield, and the residuals of this relationship were unrelated to year of release. Yield increase was associated with changes in thermal time to critical growth stages, as modern varieties had shorter vegetative period and longer grain filling period. Yield gains also derived from more kernels m-2 resultant from more kernels head-1. Historical varieties were taller, had thinner stems, and allocated more biomass to the stem than semidwarf varieties. Yield gains resulted from increases in harvest index and not in biomass accumulation at grain filling and maturity, as shoot biomass was similar among varieties. The allometric exponent (i.e., the slope between log of organ biomass and log of shoot biomass) for grain increased with, and for leaves was unrelated to, year of release. The ability of modern varieties to allocate more biomass to the kernels coupled to an early maturity increased grain yield and grain N-removal over time. However, increases in grain yield were greater than increases in grain N-removal, reducing grain protein concentration in modern varieties.

Effects of long-term herbicide application on the crops in soybean-peanut rotations in the red soil upland of Southern China

Aiming at the problem that the amount of chemical herbicides input is continuously increasing, it may be result in the severe organic chemical pollution, and the negative influence on crop growth is also enhancing in the red soil upland of southern China. Therefore, a long-term location experiment was founded to research the effects of herbicide acetochlor on the crops growth, physiology and yield in soybean-peanut rotations in the red soil upland. The data in 2013 and 2014 indicated that the rate of emergence, number of leaves, stem diameter, plant height of peanut and soybean seedlings were declined by herbicide acetochlor with long-term application, the seedling growth was limited obviously. The root nodule number, shoot dry matter and SPAD value of peanut and soybean were significantly decreased by herbicide acetochlor at four critical growing stages. Moreover, the leaf malondialdehyde (MDA) content, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of peanut were significantly decreased by acetochlor at four critical growth stages. As for soybean, the leaf MDA content at four critical growth stages and SOD and POD activities at seedling stage were significantly enhanced by acetochlor with long-term application, but SOD and POD and CAT activities at pods bearing stage and mature stage were significantly dropped. The yield components of peanut such as plant height, lateral branches number, 100 pods weight, shelling rate and yield were reduced under the treatment of herbicide acetochlor. The plant height, branches number, 100 grains weight, and grain yield of soybean were significantly decreased by the acetochlor treatment, but the empty pods rate was significantly increased. The annual yield in 12 years indicated that long-term acetochlor application reduced the yield of peanut and soybean, and the range of yield reduction was gradually aggravated with the increasing years of application. Compared with manual weeding, the yield decreasing range of soybean was from 5.64%–13.14% and the yield decreasing range of peanut was from 3.85%–12.49% under acetochlor treatment from 2006 to 2017.

Assessing the Climate Change Impacts on Grain Sorghum Yield and Irrigation Water Use under Full and Deficit Irrigation Strategies

HighlightsIrrigated grain sorghum yield and irrigation water use decreased under climate change.Increase in growing season temperature beyond 26°C resulted in a sharp decline in grain sorghum yield.Irrigating during early reproductive stages resulted in the most efficient use of limited water.Irrigating to replenish soil water to 80% of field capacity was found suitable for both current and future climates. Groundwater overdraft from the Ogallala Aquifer for irrigation use and anticipated climate change impacts pose major threats to the sustainability of agriculture in the Texas High Plains (THP) region. In this study, the DSSAT-CSM-CERES-Sorghum model was used to simulate climate change impacts on grain sorghum production under full and deficit irrigation strategies and suggest optimal deficit irrigation strategies. Two irrigation strategies were designed based on (1) crop growth stage and (2) soil water deficit. For the first strategy, seven deficit irrigation scenarios and one full irrigation scenario were simulated: three scenarios with a single 100 mm irrigation scheduled between panicle initiation and boot (T1), between boot and early grain filling (T2), and between early and late grain filling (T3) growth stages; three 200 mm irrigation treatments with combinations of T1 and T2 (T4), T1 and T3 (T5), and T2 and T3 (T6); one 300 mm irrigation scenario (T7) that was a combination of T1, T2, and T3; and a full irrigation scenario (T8) in which irrigation was applied throughout the growing season to maintain at least 50% of plant-available water in the top 30 cm soil profile. For the second strategy, the irrigation schedule obtained from auto-irrigation (T8) was mimicked to create a full irrigation scenario (I100) and six deficit irrigation scenarios. In the deficit irrigation scenarios, water was applied on the same dates as scenario I100; however, the irrigation amounts of scenario I100 were reduced by 10%, 20%, 30%, 40%, 50%, and 60% to create deficit irrigation scenarios I90, I80, I70, I60, I50, and I40, respectively. Projected climate forcings were drawn from nine global climate models (GCMs) and two representative concentration pathways (RCP 4.5 and RCP 8.5). Climate change analysis indicated that grain sorghum yield under full irrigation was expected to be reduced by 5% by mid-century (2036 to 2065) and by 15% by late-century (2066 to 2095) under RCP 8.5 compared to the baseline period (1976 to 2005). Simulated future irrigation water demand of grain sorghum was reduced due to the shorter growing season and improved dry matter- and yield-transpiration productivity, likely due to CO2 fertilization. Based on the simulated grain sorghum yield and irrigation water use efficiency, the most efficient use of limited irrigation was achieved by applying irrigation during the early reproductive stages of grain sorghum (panicle initiation through early grain filling). A 20% deficit irrigation scenario was found to be optimal for current and future conditions because it was more water use efficient than full irrigation with a minor yield reduction of <11%. In summary, these results indicated that strategic planning of when and how much to irrigate could help in getting the most out of limited irrigation. Keywords: CERES-Sorghum, Critical growth stages, Crop yield, Global climate model, Irrigation demand, Soil water depletion.

Yield, quality and drought sensitivity of tomato to water deficit during different growth stages

In areas where the supply of water for irrigation is limited, tomato production is often subject to drought stress. In order to investigate the drought sensitivity of tomato (Lycopersicon esculentum Mill.) yield and quality during different growth stages, field and pot experiments were conducted in a high tunnel in southern China during the 2013 and 2016 growing seasons. The experiments consisted of four treatments. Crops were drip-irrigated to 100 % of field capacity at all growth stages divided into treatment T1 (control) and the treatment group T2, T3 and T4 receiving half the amount of irrigation as T1 when the soil water content reached 70 % of field capacity, the vegetative phase (stage I) T2, the flowering and fruit development phase (stage II) T3, and the fruit ripening phase (stage III) T4. Compared to the control treatment, drought stress at stages II and III caused a decrease in yield of 13 % and 26 %, respectively. Fruit firmness and color index were positively affected by drought stress, while fruit water content and shape index did not show any differences between treatments. Taste and nutritional quality parameters, such as total soluble solids, soluble sugar, organic acids and vitamin C improved in response to limited water supply (p ≤ 0.05). Despite having a negative effect on fruit yield, drought stress applied at stage III tended to enhance fruit quality traits. This study found that applying drought stress at stage I can be a positive management approach as it saves water and has fewer negative effects compared to applying drought stress at the other critical growth stages, thereby minimizing the adverse effects of drought stress.

Scheduling Supplementary Irrigation for Maize Production: Analysis of the Requirements for Climate Smart Farming for Rural Development

The erratic rainfall pattern in sub Saharan Africa is a major threat to rainfed agriculture by consistently reducing yield due to water deficit and threatening food security. In order to address this problem, supplementary irrigation during the raining season is increasingly being encouraged to reduce water deficits during dry spells. The aim of this study is to design a supplementary irrigation for maize cropping during the raining season by using climatic data and water from surface runoff from a nearby catchment area. Climatic data for the study area was used to analyse the water requirement of maize during the rainy season and to propose an irrigation schedule. The results indicated that, out of 620.00 mm (3100 m3) water requirement for the entire growing cycle of maize on a 0.5 ha field, the supplementary irrigation water requirement represents more than a third of the water need of maize during periods of dry spell in the maize crop cycle. With a reservoir volume of 600.00 m3 and a net irrigation application of 60 mm (300 m3), about 5 irrigation applications (with a flow rate of 25.00 m3/hr for 6 hours a day) is required to supplement the irrigation water requirement of maize that can help alleviate soil moisture stress and increase crop yield during critical growth stages.

Agronomic, physiological and molecular characterisation of rice mutants revealed the key role of reactive oxygen species and catalase in high-temperature stress tolerance.

Climatic variations have increased the occurrence of heat stress during critical growth stages, which negatively affects grain yield in rice. Plants adapt to harsh environments, and particularly high-temperature stress, by regulating their physiological and biochemical processes, which are key tolerance mechanisms. The identification of heat-tolerant rice genotypes and reliable selection indices are crucial for rice improvement programs. Here, we evaluated the response of a rice mutant population for high-temperature stress at the seedling and reproductive stages based on agronomic, physiological and molecular indices. Estimates of variance components revealed significant differences (P < 0.001) among genotypes, treatments and their interactions for almost all traits. The principal component analysis showed significant diversity among genotypes and traits under high-temperature stress. The mutant HTT-121 was identified as the most heat-tolerant mutant with higher grain yield, panicle fertility, cell membrane thermo-stability (CMTS) and antioxidant enzyme levels under heat stress. Various seedling-based morpho-physiological traits (leaf fresh weight, relative water contents, malondialdehyde, CMTS) and biochemical traits (superoxide dismutase, catalase and hydrogen peroxide) explained variations in grain yield that could be used as selection indices for heat tolerance in rice during early growth. Notably, heat-sensitive mutants accumulated reactive oxygen species, reduced catalase activity and upregulated OsSRFP1 expression under heat stress, suggesting their key roles in regulating heat tolerance in rice. The heat-tolerant mutants identified in this study could be used in breeding programs and to develop mapping populations to unravel the underlying genetic architecture for heat-stress adaptability.

Techniques of orchard establishment in arid and semi-arid regions

Orchard establishment is a long term investment, so careful planning and proper techniques of planting are prerequisites. There are two ways of orchards arranged i.e., traditional and modern or high density planting. In arid and semi arid conditions its more matter in context of location/site, crops & its varieties selection as well as techniques of planting and after care over other climatic regions. This region mostly having fragile ecosystem (unpredictable weather, limited and erratic rainfall) and poor in soil organic matter and available nutrients as well as other conditions for normal growth and development of the plant. Most suitable arid fruit crops are ber, ker, lasoda, pomegranate, fig, date palm, karonda, phalsa etc or having xerophytic adaptation, similarly semi-arid region potential crops are sweet orange, lime, jamun, khirni, bael, guava, aonla, custard apple, tamarind, mahua, chironji etc or possessing phonological adjustment (critical growth stage completion in optimum moisture available season). Apart from adaptations proper care and management techniques are require for sustainable/ potential production of these fruit crops in this region.

Effect of household waste based vermicompost and fertilizer on phosphorus and potassium mineralization in calcareous soil of Bihar

An incubation experiment was conducted during Kharif 2018 at RPCAU, Pusa to examine the mineralization of vermicompost in calcareous sandy loam soil at five different stages which match with the critical growth stages of rice crop and the experiment was conducted in Completely Randomized design (3 factors) replicated thrice. There were four levels of vermicompost along with three levels of chemical fertilizers used at field capacity (19.47%) in combinations and alone. Results indicated that content of available P2O5 and K2O in soil increased up to 65 DAI then decreased gradually. Application of increasing level of vermicompost and fertilizer alone or in combination resulted in corresponding increase in the available nutrient content of soil. During the study, it was observed that the treatment combination involving application of highest dose of vermicompost (3.75 t ha-1) along with full dose of fertilizer (RDF) was significantly superior.

Nationwide crop yield estimation based on photosynthesis and meteorological stress indices

There is considerable demand for nationwide grain yield estimation during the cropping season by growers, grain marketers, grain handlers, agricultural businesses, and market brokers. In this paper, we developed a semi-empirical model (Crop-SI) to estimate the yield of the three major crops in the dryland Australian wheatbelt by combining a radiation use efficiency approach with meteorology driven Stress Indices (SI) at critical crop growth stages (e.g., anthesis and grain filling). These crop-specific SI (e.g., drought, heat and cold stress) help explain the impact of high spatial agro-environmental heterogeneity, which lead to substantial improvement in grain yield prediction. Crop-SI explains 87%, 69% and 83% of the observed field-scale grain yield variability with root mean square error of ~0.4, 0.4 and 0.5 t/ha for canola, wheat, and barley, respectively. At the pixel-level, Crop-SI reduces the relative error in grain yield estimation to 34%, 25%, and 20% for canola, wheat, barley, respectively, compared to two benchmark models. By incorporating water- and temperature-driven stresses, Crop-SI's predictive skill in highly variable environments is enhanced. As such, it paves the way for the next generation of agricultural systems models, knowledge products and decision support tools that need to operate at various scales.

Effect of potassium and sulphur levels on available K2O and available sulphur at critical growth stages at harvest of groundnut

Effect of potassium and sulphur levels on available K2O and available sulphur at critical growth stages at harvest of groundnut

The synchrony of cover crop decomposition, enzyme activity, and nitrogen availability in a corn agroecosystem in the Midwest United States

Cover cropping is commonly associated with increased soil microbial activity and soil health. Cover cropping in the Upper Mississippi River Basin has increased rapidly in the last decade due to the demonstrated ability that cover crops can increase soil health and decrease nitrate losses in tile-drained fields. One reason cover cropping is not adopted in the Midwest United States is the lack of knowledge on the synchrony of cover crop residue nitrogen (N) release and corn N demand. Therefore, the overarching goal of this research was to investigate soil enzyme activity and inorganic N availability during the decomposition period of common winter cover crops. Objectives were: i) to determine if soil enzyme activity (β-glucosidase and urease) is influenced by different cover crops (cereal rye (CR), hairy vetch (HV), and HV/CR mixture) and tillage systems (reduced tillage and no-tillage residue management) during the residue decomposition period, and ii) to determine the relationship between soil enzyme activity, inorganic N availability, and critical corn growth stages during cover crop decomposition. Cover crops in this study were selected due to contrast in residue carbon (C):N ratios, their commonality among regional farmers, and their differences in physiology. Spring tillage and no-tillage were investigated because of the differing levels of soil disturbance and residue incorporation. Enzyme activities were quantified at seven sampling dates following cover crop termination from April-October during the 2016 and 2017 corn growing seasons. Results revealed significant effects of sampling date (p < 0.001) and cover crop treatment (p < 0.05) on soil β-glucosidase activity and significant interaction effects between sampling date and cover crop treatment (p < 0.05) on potential soil urease activity. Tillage had a significant impact on soil β-glucosidase (p < 0.001) and urease (p < 0.05) activities in 2017, with higher activity observed in the no-tillage soil. These findings indicate that enzyme activity fluxes can be observed in agroecosystems one year after introducing conservation practices, such as cover crops and no-tillage. Greater than 50 % of C release from cover crop residue occurred from corn emergence to tasseling, and significantly greater β-glucosidase activity for CR-based treatments during corn peak N demand did not result in more soil inorganic N. This indicates a loss of plant-available N from the agroecosystem, which could be attributed to N immobilization by the soil microbial community. This study demonstrates a need to develop adaptive N fertilization management for corn that can overcome the potential impact of N immobilization during peak corn N demand following CR.

Estimation of Nitrogen Nutrition Status in Winter Wheat From Unmanned Aerial Vehicle Based Multi-Angular Multispectral Imagery

Rapid, non-destructive and accurate detection of crop N status is beneficial for optimized fertilizer applications and grain quality prediction in the context of precision crop management. Previous research on the remote estimation of crop N nutrition status was mostly conducted with ground-based spectral data from nadir or oblique angles. Few studies investigated the performance of unmanned aerial vehicle (UAV) based multispectral imagery in regular nadir views for such a purpose, not to mention the feasibility of oblique or multi-angular images for improved estimation. This study employed a UAV-based five-band camera to acquire multispectral images at seven view zenith angles (VZAs) (0°, ± 20°, ± 40° and ±60°) for three critical growth stages of winter wheat. Four representative vegetation indices encompassing the Visible Atmospherically Resistant Index (VARI), Red edge Chlorophyll Index (CIred-edge), Green band Chlorophyll Index (CIgreen), Modified Normalized Difference Vegetation Index with a blue band (mNDblue) were derived from the multi-angular images. They were used to estimate the N nutrition status in leaf nitrogen concentration (LNC), plant nitrogen concentration (PNC), leaf nitrogen accumulation (LNA), and plant nitrogen accumulation (PNA) of wheat canopies for a combination of treatments in N rate, variety and planting density. The results demonstrated that the highest accuracy for single-angle images was obtained with CIgreen for LNC from a VZA of -60° (R2 = 0.71, RMSE = 0.34%) and PNC from a VZA of -40° (R2 = 0.36, RMSE = 0.29%). When combining an off-nadir image (-40°) and the 0° image, the accuracy of PNC estimation was substantially improved (CIred-edge: R2 = 0.52, RMSE = 0.28%). However, the use of dual-angle images did not significantly increase the estimation accuracy for LNA and PNA compared to the use of single-angle images. Our findings suggest that it is important and practical to use oblique images from a UAV-based multispectral camera for better estimation of nitrogen concentration in wheat leaves or plants. The oblique images acquired from additional flights could be used alone or combined with the nadir-view images for improved crop N status monitoring.

English

Chickpea pod borer (Helicoverpa armigera) is a major insect pest constraining chickpea production in Tigray, northern Ethiopia, as there is no recommended management option in the area. Therefore the present study was conducted to assess the efficacy of insecticides and to determine the critical growth stage of the crop for effective spray at Axum Agricultural Research Center. Results indicated that in laboratory profit 72% EC (profenofos), abema 3% EC (abamectin 20 g/L + emamectin benzoit 10 g/L), perfecto (imedachloprid + lambda-cyhalothrin) and hamectin (abamectin) reduced the number of larvae by 75, 55, 44 and 34%; 86, 82, 65, 56% and 83, 83, 66 and 83% at 24, 48 and 72 h after spray, respectively. Similarly abema 3%EC and profit (Profenofos) 72% EC were the most effective insecticides to give high mortality of pod borer on chickpea under field conditions. These insecticides reduced the number of larva per plant by 51 to 56.7% five days after spray. The number of damaged pods per plant was very low in both insecticides (0.91 and 1.05) but on the untreated check 3.05. The highest yield was also obtained from chickpea treated with abema 3%EC at podding stage (23.92 qt/ha). Comparatively the most effective insecticides against pod borer were abema and profit and the best application time were at podding stage of the crop. Thus chickpea growers in the area should prefer these insecticides for better pod borer management. Key words: Chickpea, Helicoverpa armigera, insecticides, growth stage.

Soil water extraction and use by winter wheat cultivars under limited irrigation in a semi-arid environment

Water supply and distribution are the main limiting factors to wheat (Triticum aestivum) yield in a semi-arid region of the U.S. southern Great Plains. To manage crop water demand, limited irrigation (also called deficit irrigation) is commonly practiced in the region. A 4-yr study was conducted to evaluate yield in winter wheat cultivars as influenced by the depth and amount of net soil water extraction (SWE) under limited irrigation. For timing the irrigation application, we considered critical growth stages (jointing, tillering, and anthesis) as well as soil water depletion at the crop root zone below 50%. Volumetric soil water content was measured in 0.2 m increments to the depth of 2.4 m at planting, jointing, anthesis, and physiological maturity. Since the irrigation capacity was limited, seasonal precipitation was still an important factor for determining SWE. The 2011 season was one of the historic drought seasons with only 60 mm of seasonal precipitation and the net SWE in that season was limited to the upper 1.2 m profile. In contrast, the 2016 season was more favorable for crop growth with 315 mm of seasonal precipitation and the net SWE in that season reached to 2.0 m deep. Grain yield was largely influenced by the amount of net SWE during the growing season. For the wheat with grain yield of 4807 kg ha−1, net SWE was 165 mm (2016). However, wheat with grain yield of 2933 kg ha−1 only extracted 70 mm stored soil water (2011). The 2012 and 2017 seasons remained intermediate in terms of seasonal precipitation, SWE, and yield. Although the 2011 and 2016 seasons had similar stored soil moisture at planting, more early-season as well as total precipitation in 2016 appears to have enabled plant growth to access the deeper water. In contrast, a greater amount of stored soil water was left unused at the end of the 2011 season due to drought and poor plant growth. Hence, in addition to adding water at critical growth stages, ensuring early plant growth to promote root development for extracting soil water from the deeper profile later in the season should be a key strategy to take full advantage of limited irrigation.

Principal variable selection to explain grain yield variation in winter wheat from features extracted from UAV imagery

BackgroundAutomated phenotyping technologies are continually advancing the breeding process. However, collecting various secondary traits throughout the growing season and processing massive amounts of data still take great efforts and time. Selecting a minimum number of secondary traits that have the maximum predictive power has the potential to reduce phenotyping efforts. The objective of this study was to select principal features extracted from UAV imagery and critical growth stages that contributed the most in explaining winter wheat grain yield. Five dates of multispectral images and seven dates of RGB images were collected by a UAV system during the spring growing season in 2018. Two classes of features (variables), totaling to 172 variables, were extracted for each plot from the vegetation index and plant height maps, including pixel statistics and dynamic growth rates. A parametric algorithm, LASSO regression (the least angle and shrinkage selection operator), and a non-parametric algorithm, random forest, were applied for variable selection. The regression coefficients estimated by LASSO and the permutation importance scores provided by random forest were used to determine the ten most important variables influencing grain yield from each algorithm.ResultsBoth selection algorithms assigned the highest importance score to the variables related with plant height around the grain filling stage. Some vegetation indices related variables were also selected by the algorithms mainly at earlier to mid growth stages and during the senescence. Compared with the yield prediction using all 172 variables derived from measured phenotypes, using the selected variables performed comparable or even better. We also noticed that the prediction accuracy on the adapted NE lines (r = 0.58–0.81) was higher than the other lines (r = 0.21–0.59) included in this study with different genetic backgrounds.ConclusionsWith the ultra-high resolution plot imagery obtained by the UAS-based phenotyping we are now able to derive more features, such as the variation of plant height or vegetation indices within a plot other than just an averaged number, that are potentially very useful for the breeding purpose. However, too many features or variables can be derived in this way. The promising results from this study suggests that the selected set from those variables can have comparable prediction accuracies on the grain yield prediction than the full set of them but possibly resulting in a better allocation of efforts and resources on phenotypic data collection and processing.

Mitigating crop yield losses through weed diversity

Reconciling crop productivity and biodiversity maintenance is one of the main challenges of agriculture worldwide. Moreover, the importance of weed diversity in mitigating yield losses has been identified as one of the top five research priorities in weed science. We tested the hypotheses that (1) not all weed communities generate yield losses and (2) that more diversified weed communities can mitigate yield losses. The study is based on three years of observations of weed densities, weed biomass and crop biomass at four critical growth stages of winter cereals across 54 zones (36 unweeded and 18 weeded). Out of the six communities identified, only four generated significant yield losses in unweeded zones, ranging from 19% to 56%. The number of ears per plant and the number of grains per ear were systematically affected. Only one weed community was capable of reducing 1,000-kernel weight. Weed biomass decreased by 83% over the gradient of weed community evenness, whereas crop productivity increased by 23%. Diversified weed communities limited the negative effect of competitive and dominant species on crop productivity while potentially promoting ecosystem services provided by subordinate species. Reducing herbicides exposes crops to yield losses from weeds. This study on winter wheat and barley finds that more even weed communities reduce yield losses by suppressing dominant weeds.

Using High-Spatiotemporal Thermal Satellite ET Retrievals for Operational Water Use and Stress Monitoring in a California Vineyard

In viticulture, deficit irrigation strategies are often implemented to control vine canopy growth and to impose stress at critical stages of vine growth to improve wine grape quality. To support deficit irrigation scheduling, remote sensing technologies can be employed in the mapping of evapotranspiration (ET) at the field to sub-field scales, quantifying time-varying vineyard water requirements and actual water use. In the current study, we investigate the utility of ET maps derived from thermal infrared satellite imagery over a vineyard in the Central Valley of California equipped with a variable rate drip irrigation (VRDI) system which enables differential water applications at the 30 × 30 m scale. To support irrigation management at that scale, we utilized a thermal-based multi-sensor data fusion approach to generate weekly total actual ET (ETa) estimates at 30 m spatial resolution, coinciding with the resolution of the Landsat reflectance bands. Crop water requirements (ETc) were defined with a vegetative index (VI)-based approach. To test capacity to capture stress signals, the vineyard was sub-divided into four blocks with different irrigation management strategies and goals, inducing varying degrees of stress during the growing season. Results indicate derived weekly total ET from the thermal-based data fusion approach match well with observations. The thermal-based method was also able to capture the spatial heterogeneity in ET over the vineyard due to a water stress event imposed on two of the four vineyard blocks. This transient stress event was not reflected in the VI-based ETc estimate, highlighting the value of thermal band imaging. While the data fusion system provided valuable information, latency in current satellite data availability, particularly from Landsat, impacts operational applications over the course of a growing season.