Reduction In Harvest Index Research Articles

Is interannual grain yield decline of intermediate wheatgrass influenced by management and climate in the Upper Midwest?

Perennial crops have the potential to provide sustainable food production while promoting multiple ecosystem services. Intermediate wheatgrass (IWG) is a perennial grass that is currently being domesticated as a perennial grain crop. However, one major hurdle limiting producer adoption is its interannual grain yield decline. While such a phenomenon has an evolutionary basis and has been reported in other perennial grain crops, there are currently conflicting reports about the extent of this phenomenon in IWG. To address this challenge, we have assembled a unique dataset integrating 13 field experiments conducted by the same research team in Minnesota, USA where IWG yield trials were established over 3–4 years, covering 24 location-years representing 9 treatments and up to 3424 plot-level yield observations. Our goals were to 1) determine the extent and magnitude of IWG yield decline and 2) examine the relative contribution of crop management and climate in mitigating IWG yield decline if it exists. Our results indicate that IWG grain yield decline starts during the second production year in Minnesota and continues annually at an average rate of 200–225 kg ha−1 yr−1, driven by a reduction in harvest index which declined at a rate of 2% yr−1. This decline occurred regardless of crop management practices, but some approaches, particularly optimal nitrogen application, plant density and cultivar choice increased grain yield potential. IWG productivity was also influenced by environmental gradients, with the strongest effect attributable to rising atmospheric drought or vapor pressure deficit (VPD), which influenced yield decline locally. Overall, the analysis indicated that optimal management, in concert with breeding towards more productive and climate-resilient varieties have the potential to reduce IWG decline in Minnesota.

Impact of Low Light Stress on Physiological Characters, Yield and Yield Attributes of Rice (Oryza sativa L.)

Background: Keeping in view of low light effect on rice yield and quality, identification of low light tolerant genotypes as donor for plant breeding program is needed. Methods: Field experiments were conducted for low light tolerance during kharif 2021 at Regional Agricultural Research Station, Maruteru with an aim to screen and identify low light tolerant cultivars. The impact of low light was investigated on physiological, yield and yield attributes of eighteen rice genotypes. Result: Low light treatment resulted and increase in mean days to 50% flowering and days to maturity. An increment of both plant height and leaf area was noted under low light stress in all the tested genotypes. Yield and yield attributes such as panicle number, grain number per panicle and test weight were also affected. The reduction in total dry matter and harvest index was recorded on exposure to low light condition. Under low light grain yield was maximum in IET 29032 followed by IET 30408 and Gayatri and these were identified as low light tolerant genotypes. These genotypes had a higher panicle number. Genotype Gayatri showed maximum 1000 grain weight and minimum reduction in harvest index was evident in IET 29032 and IET 30408. The chlorophyll a pigment content reduced under low light while majority of the genotypes showed an increase in chlorophyll b pigment. Gayatri followed by IET 29032 and IET 30408 retained higher chlorophyll content under low light stress. Lesser reduction in chlorophyll content (less than 13%) was evident in IET 30408, Gayatri, Swarnaprabha, IET 29031 and IET 29032.

Effect of Auxin and Nitrogen on Seed Yield And Germination Traits of Produced Wheat Seeds

Field and laboratory experiments were conducted to assess the response of wheat to external auxin application and nitrogen. Studied factors in the field experiment were different concentrations of auxin (0, 50, and 100 ppm) and nitrogen fertilizer application (0, 75, and 150 kg/ha). In the laboratory experiment, germination traits of produced seeds from maternal plants under the field experiment treatments were assessed. Results showed that no auxin application with nitrogen application had higher stem and leaf yield than auxin application of 50 ppm with nitrogen application of 150 kg/ha. Under high nitrogen application, the negative effect of external auxin on seed yield occurred at a lower concentration. Under nitrogen application of 75 kg/ha, auxin application of 100 ppm reduced harvest index and seed weight. Nitrogen application reduced seed germination percentage but auxin broke the negative effect of nitrogen on seed germination.

Elevated CO2 Could Reduce Spikelet Fertility and Grain Appearance Quality of Rice(Oryza sativa L.) Grown under High-temperature Conditions

Two Japanese rice cultivars with different heat-tolerance, Hinohikari (sensitive) and Nikomaru (tolerant), were grown in pots inside open-top chambers and exposed to ambient CO2 (400 µmol mol−1) or elevated CO2 (550 µmol mol−1) from the beginning of the tillering stage to maturity. The study was conducted in Nagasaki, in the Kyushu region of Japan, where heat stress on rice has become increasingly evident. Although elevated CO2 significantly improved the net photosynthesis and whole-plant growth of the cultivars, there were no significant effects on grain yield, which in turn reduced harvest index. In both cultivars, adverse effects occurred with elevated CO2, such as reductions in spikelet fertility and grain appearance quality, which are typical manifestations of heat stress in rice. During the flowering period, the air temperature was high that spikelet fertility was reduced even under ambient CO2 conditions for both cultivars. These results suggest that, under high-temperature conditions, elevated CO2 could induce or exacerbate the manifestations of heat stress in rice. Because transpiration rate in the flag leaf was significantly reduced by the exposure to elevated CO2, it is possible that elevated CO2 increased plant temperature via a reduction in transpiration during flowering period, although we did not detect significance of the increase in leaf and panicle temperature. To ensure a more confident conclusion, further studies focusing on the effects of elevated CO2 on the determinants of spikelet fertility and grain appearance quality with other cultivars in different year are required.

Genotypic variation in the response of soybean to elevated CO2.

The impact of elevated CO2 (eCO2) on soybean productivity is essential to the global food supply because it is the world's leading source of vegetable proteins. This study aimed to understand the yield responses and nutritional impact under free-air CO2 enrichment (FACE) conditions of soybean genotypes. Here we report that grain yield increased by 46.9% and no reduction in harvest index was observed among soybean genotypes. Elevated CO2 improved the photosynthetic carbon assimilation rate, leaf area, plant height, and aboveground biomass at vegetative and pod filling stages. Besides the positive effects on yield parameters, eCO2 differentially affected the overall grain quality. The levels of calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), manganese (Mn), iron (Fe), boron (B), and zinc (Zn) grain minerals decreased by 22.9, 9.0, 4.9, 10.1, 21.3, 28.1, 18.5, and 25.9% under eCO2 conditions, respectively. Soluble sugars and starch increased by 9.1 and 16.0%, respectively, phytic acid accumulation increased by 8.1%, but grain protein content significantly decreased by 5.6% across soybean genotypes. Furthermore, the antioxidant activity decreased by 36.9%, but the total phenolic content was not affected by eCO2 conditions. Genotypes, such as Winsconsin Black, Primorskaja, and L-117, were considered the most responsive to eCO2 in terms of yield enhancement and less affected in the nutritional quality. Our results confirm the existence of genetic variability in soybean responses to eCO2, and differences between genotypes in yield improvement and decreased sensitivity to eCO2 in terms of grain quality loss could be included in future soybean selection to enable adaptation to climate change.

Interactive Effects of Elevated Ozone and Temperature on Growth and Yield of Soybean (Glycine max (L.) Merr.) under Field Conditions

Elevated ozone and rising temperature are both factors in climate change, but they are difficult to study in combination due to exposure system requirements. We developed and deployed an air exclusion exposure system to treat soybean (Glycine max (L.) Merr.) cultivar “Jake” with season-long combinations of sub-ambient ozone (18 ppb, 12 h mean), elevated ozone (66 ppb, 12 h mean), and elevated temperature (+3.5 °C daytime, +2.4 °C nighttime) in irrigated field plots. Warming caused a shift in biomass partitioning from reproductive tissues into stems and petioles at mid-season that resulted in a significant 25% reduction in final seed yield and a significant reduction in harvest index. The elevated ozone treatment delayed mid-season biomass production, and final seed yield was reduced by a non-significant 2%. However, there were significant underlying effects of elevated ozone on seed production. The non-significant impact of ozone on seed yield of cultivar “Jake” resulted from significant increases in pod number (+16%) and seed number (+18%) that were offset by a significant reduction in seed size (−16%). No evidence of significant warming–ozone interactions was found in biomass or seed yield responses. In general, significant impacts of the individual warming or ozone treatments were found to be additive.

Agro‐Economic Returns were Reduced for Four Years after Conversion from Perennial Forage

Perennial crops are increasingly converted to annual cropping systems as Conservation Reserve Program (CRP) contracts expire. We compared crop yields and net returns across 2013–2018 for no‐till pulse crop‐wheat (Triticum aestivum L.) (P‐W) systems, preceded either by 10 yr of P‐W or 10 yr of perennial cropping (P‐WPer) at Bozeman, MT. The perennial mixed species planting, dominated by alfalfa (Medicago sativa L.), was split into unharvested and annually harvested treatments 2005–2012. The 2013–2018 experimental design included both systems replicated as main plots, with 50 and 100% recommended available N rates as subplots. Precipitation was below average during three of the first four growing seasons, followed by two wetter than average years. The P‐WPer system had generally lower soil moisture and equal or greater nitrogen supply than the P‐W. ‘Haying off’ (reduced harvest index) occurred in wheat grown 2 and 4 yr after conversion from perennial to annual cropping, which reduced grain yield, and increased grain protein. Crop yield losses in the P‐WPer system averaged 0.84 Mg ha–1 (28%) over 4 yr and two N rates. After adjusting grain prices using historical discounts and premiums for test weight and protein content at Montana grain elevators, P‐WPer net returns were reduced for four consecutive years in three economic scenarios, and for 2 yr in a fourth scenario by a 4‐yr cumulative average of (USD) $731 ha–1 (45%). We conclude annual crop yield and economic returns were compromised for 4 yr following 10 yr of an alfalfa‐dominated perennial cropping system.Core Ideas Ten years of perennial forage generally reduced economic returns for 4 yr of subsequent annual cropping by an average of 45%. Grain yield was more negatively affected by perennial cropping than protein yield. Long‐term assessment may be required to capture economic benefits of improved soil quality.

Yield response to heat stress as affected by nitrogen availability in maize

Maize yield has to be increased in the next decades in order to satisfy world demand. This increase has to be achieved in a scenario of climate change particularly characterised by heat stress. Several agronomic and genetic strategies for increased tolerance to high temperatures will be necessary. Some results in other crops showed interactions between high temperature stress and nitrogen (N) availability. To the best of our knowledge, this interaction has not been tested in maize. Therefore, the aim of this study was to explore, under field conditions, whether the magnitude of yield penalty imposed by elevated canopy air temperature around flowering or during early grain filling is affected by N availability. In particular we aimed to (i) quantify the magnitude of yield losses by heat stress around flowering and during early grain filling, (ii) determine whether N fertilisation affects these magnitudes, and (iii) identify whether the effects are indirect (through affecting growth) or directly on the grain set and/or grain growth capacity. Four field experiments were carried out during four consecutive years in NE Spain. The treatments consisted in a factorial combination of one or two hybrids, two or three levels of N fertilisation and three temperature conditions. The temperature treatments consisted of a control (plots grown under natural temperature throughout the growing season) and two treatments in which the temperatures of the canopy were increased in the field for relatively short periods. All experiments were well watered to avoid water stress.The elevated canopy air temperature treatment only increased the maximum temperature in a relatively small magnitude (mean daily temperature was increased at the ears height by c. 1°C each day of treatment). However, yield penalty imposed by heat stress was in general very noticeable and dramatic when the treatment included the critical period for grain number determination, around silking. The damage was much stronger in the long- than in the short-cycle hybrid. Exposing the plants to elevated canopy air temperature during the critical period reduced harvest index, from values of around 46% in unheated conditions to 20% under elevated canopy air temperature, being the reduction higher under N200 than under N0 fertilisation treatments.As far as we are aware, we showed for the first time in maize grown in field conditions, that the losses in yield in response to elevated canopy air temperature treatment were magnified by the N availability. The effect of N on emphasising the penalties seemed not to be a direct effect of this nutrient but and indirect effect through affecting growth. The effect was through affecting the capacity of the plants to set grains and to a lesser extent to allow grain weight to be maximised; and it was independent of any (potentially additional) effects on either uncoupling anthesis and silking or on pollen amount and viability.

Amelioration of salinity on photosynthesis and some characteristics of three rapeseed (Brassica napus) cultivars under increased concentrations of carbon dioxide

This study was done to evaluate the effects of increasing concentrations of CO2 (CC) on rapeseed. Pot experiments were done with three cultivars (Okapi, Zarfam and RGS003) of rapeseed (Brassica napus) for salinity tolerance. Four levels of salinity (0, 5, 10 and 15 dS m−1) were tested on the three cultivars at three CC (350, 700 and 1050 mmol L−1) at the greenhouse of Tarbiat Modares University, Iran, during the crop seasons of 2010 to 2011. Three CCs were considered as three environments and the other two treatments (salinity and cultivar) were tested within these environments in a complete block design arranged as a factorial. Results indicated that photosynthetic rates declined with increasing levels of salinity. Elevated CC significantly increased rates of photosynthesis. The highest CC reduced the impact of salinity on photosynthesis. Increased CC reduced the rate of transpiration, which had the effects of increasing rates of photosynthesis and water use efficiency (WUE); these effects increased vegetative growth and reduced the adverse effects of salinity. Increased CC and salinity reduced harvest index. WUE increased with CC increment, and decreased with salinity elevation.

Physiological analyses of traits associated with tolerance of long-term partial submergence in rice.

Floods are major constraints to crop production worldwide. In low-lying, flood-prone areas of the tropics, longer-term partial submergence (stagnant flooding [SF]) greatly reduces rice yield. This study assesses shoot growth and several physiological mechanisms associated with SF tolerance in rice. Five rice genotypes with contrasting responses to SF were evaluated in field ponds. Following transplanting, floodwater was gradually increased at a rate of ∼2 cm day(-1) to reach a final depth of 50 cm and then maintained until maturity. Although plants were not fully submerged, the yield was reduced by 47 % across genotypes compared with those grown under control conditions (6.1 vs. 3.3 t ha(-1)). This reduction was mainly attributed to the reduction in biomass caused by reduced light interception and leaf growth above the water. Stagnant flooding also reduced panicle number per unit area by 52 % because of reduced tillering. Shoot elongation rate kept pace with rising floodwater and correlated positively with leaf growth and biomass production. Conversely, stem non-structural carbohydrate (NSC) concentration correlated negatively with shoot elongation rate, suggesting that fast-elongating genotypes actively consume NSCs to avoid complete submergence. Moderate shoot elongation rate strongly and positively correlated with grain yield under SF; however, elongation at rates >2.0 cm day(-1) was associated with reduced harvest index due to a smaller panicle size and increased lodging. Tolerant varieties were found to be either inherently tall or elongate moderately with rising floodwater. Our studies suggest that to improve tolerance of SF an appropriate phenotype should combine both of these traits. Fine-tuning for optimum shoot elongation with rising floodwater is, therefore, a priority for future work.

Effect of pre-sowing plants and different nitrogen levels on the yield and yield components of wheat (Triticum aestivum L.)

A field experiment was conducted to determine the most appropriate level of nitrogen fertilizer and wheat presowing plants during 2012- 2013 sowing season under the temperate climate of Ilam province, IRAN. The experiment was performed in a split plot arrangement based on randomized complete block design with 4 replications. The main plots consisted of 6 pre-sowing plant treatments (control, Perko PVH, Buko, Clover, Oilseed radish and the combination of three plants Ramtil, Phacelia and clover), and sub-plots were allocated to four levels of nitrogen fertilizer (0, 75, 150 and 225 kg/ ha ). The results showed that there were significant differences among the treatments for the biological yield, total dry weight, protein content, protein yield and the percentage of organic carbon in soil after planting. Boko and Perko produced the highest yield as a pre-sowing plant. The type of Pre-sowing plant significantly affected grain yield, number of spikelets per spike and harvest index. However, the effect of pre-sowing plant type was not significant on the number of grains per spike, thousand grain weight, spike number and grain weight per spike. Increasing the nitrogen levels significantly improved the number of spikelets per spike, grains per spike, grain weight, and the number of spikes per unit area. However, there was a reduction in harvest index and grain weight per spike by increasing the levels of nitrogen. The highest wheat grain yield (8440.8 kg ha -1 ) was achieved at 150 kg N ha -1 and the lowest (5039 kg ha -1 ) belonged to control (no N fertilizer). The highest and lowest grain yields were obtained for Buko and no pre-sowing plant with 8345, and 4491 kg ha-1, respectively.

Impact of primary treated sewage water on the chemical composition of safflower oil as a potential candidate for biodiesel production

Biodiesel is gaining expanded interest all over the world. It is considered a renewable source of energy. In this work, safflower was irrigated with primary treated sewage water (PTSW) without fertilization and the extracted seed oil was transesterified to yield biodiesel. Harvest index and oil yield was compared to that irrigated with fresh water (FW). Physical properties for both oils and their parent biodiesels were carried out i.e. viscosity, specific gravity, Iodine value, and cetane number for biodiesel (CN) and chemical composition using gas chromatography.A reduction in harvest index reached 47% for PTSW in comparison to FW was recorded. Also, there were many differences in physical properties (sp. gr., viscosity, and iodine value) and chemical composition (fatty acid profile) between both oils and their parent biodiesels. It was found that poly unsaturated fatty acids were increased in PTSW treatment compared to FW especially linoleic acid. The produced biodiesel complied with the standards in many aspects except CN as it was 35.2 against >54 for

Gibberellin-responsive and -insensitive dwarfing alleles on wheat performance in contrasting tillage systems

Near-isogenic lines (NILs) of winter wheat varying for alleles for reduced height (Rht), gibberellin (GA) response and photoperiod insensitivity (Ppd-D1a) in cv. Mercia background (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht8c+Ppd-D1a, Rht-D1c, Rht12) and cv. Maris Widgeon (rht (tall), Rht-D1b, Rht-B1c) backgrounds were compared to investigate main effects and interactions with tillage (plough-based, minimum-, and zero-tillage) over two years. Both minimum- and zero- tillage were associated with reduced grain yields allied to reduced harvest index, biomass accumulation, interception of photosynthetically active radiation (PAR), and plant populations. Grain yields were optimized at mature crop heights of around 740mm because this provided the best compromise between harvest index which declined with height, and above ground biomass which increased with height. Improving biomass with height was due to improvements in both PAR interception and radiation-use efficiency. Optimum height for grain yield was unaffected by tillage system or GA-sensitivity. After accounting for effects of height, GA insensitivity was associated with increased grain yields due to increased grains per spike, which was more than enough to compensate for poorer plant establishment and lower mean grain weights compared to the GA-sensitive lines. Although better establishment was possible with GA-sensitive lines, there was no evidence that this effect interacted with tillage method. We find, therefore, little evidence to question the current adoption of wheats with reduced sensitivity to GA in the UK, even as tillage intensity lessens.

Mechanisms of Yield Loss in Maize Caused by Weed Competition

The physiological process underlying grain yield (GY) loss in maize as a result of weed competition is not understood clearly. We designed an experiment to test the hypotheses that early season stress caused by the presence of neighboring weeds will increase plant-to-plant variability (PPV) of individual plant dry matter (PDM) within the population. This increase in PPV will reduce GY through a reduction in harvest index (HI). Field experiments were conducted in 2008, 2009, and 2010. A glyphosate-resistant maize hybrid was cropped at a density of 7 plants m−2. As a model weed, winter wheat was seeded at the same time as maize and controlled with glyphosate at the 3rd or 10th to 12th leaf-tip stage of maize. Weed competition early in the development of maize decreased PDM and GY. This reduction in PDM, which occurred early in the development of maize, was attributed initially to a delay in rate of leaf appearance. Reductions in PDM were accompanied by an increase in PPV of PDM. This increase in PPV, however, did not reduce HI and did not contribute to the GY reductions created by weed competition, as hypothesized. As weed control was delayed, a reduction in fraction of photosynthetically active radiation (fIPAR) accounted for a further reduction in PDM and notably, a reduction in DMA from 17th leaf-tip stage through to maturity. The rapid loss of PDM and the subsequent inability to accumulate dry matter during maturation accounted for a rapid decline in kernel number (KN) and kernel weight (KW).

Nitrogen and Potassium Fertilization Responses of Potato (Solanum tuberosum) cv. Spunta

A potato field experiment was conducted for 2 consecutive years to determine the effects of nitrogen (N) and potassium (K) fertilization rates on the yield and quality of potato cv. Spunta cultivated on soil low in N and K. A 3 × 4 complete factorial experiment was used with three rates of nitrogen (330, 495, and 660 kg N ha–1) and four rates of potassium (112, 225, 450, and 675 kg K2Ο ha–1). An additional treatment without fertilization was used as the control. On soils low in N and K, potatoes showed low yield response to K fertilizer. The greatest tuber yields for both years were achieved at 495 kg N ha–1 and 112 kg K2O ha–1 (29.81 t ha–1) and 225 kg ha–1 (27.13 t ha–1), respectively. Differences in mean fresh weight due to treatment application were not significant. Application of 495 kg N ha–1 significantly reduced harvest index (the ratio of tuber dry weight to the total dry weight at harvest) compared to 330 kg N ha–1, but at 660 kg N ha–1 harvest index achieved the greatest significant value. Potassium fertilization had no significant influence on harvest index. Nitrogen rates positively influenced the number of tubers. The addition of 450 kg K2O ha–1 significantly enhanced the number of tubers compared to the lower K rates, and the number was significantly decreased by the application of 675 kg K2O ha–1. Tuber dry-matter concentration was significantly promoted by N fertilization in both cultivation years, but it was negatively affected by K fertilization in the first year of cultivation. There was no change in tuber N with N application, but N application strongly increased nitrate (NO3) concentration, which fluctuated between 360 and 1382 mg kg–1 wet mass. Tuber NO3 was negatively correlated with tuber yield, indicating that high levels of NO3 in tubers can adversely affect yield. Tuber response to K fertilization was not in accordance with the rate of applied nutrient.

Dual-purpose use of winter wheat in western China: cutting time and nitrogen application effects on phenology, forage production, and grain yield

Conventional rainfed mixed crop–livestock systems of western China lack high-quality forage and restrict livestock production. This study explored the forage potential from wheat and its effects on subsequent grain yield. Different cutting times were imposed on winter wheat (Triticum aestivum) at Qingyang, Gansu Province, in two growing seasons, and the effect of nitrogen (N) topdressing rates (0, 60, and 120 kg N/ha) on grain yield recovery was explored. Results showed the potential to produce 0.8–1.6 t DM/ha of wheat forage with high nutritive value when cut before stem elongation (GS 30). In the wetter year, cutting before stem elongation did not delay crop development significantly (<3 days at anthesis and 5 days at maturity), but grain yields were reduced by 17–28% compared with the uncut crop (5.8 t DM/ha), mainly due to reductions in number of spikes per m2 and, consequently, number of grains per m2. In both seasons, more forage biomass was available if crops were cut later than GS 32, but this came with large reductions (>62%) in grain yield and delays in crop development (>9 days or 131 degree-days). Crops cut later than GS 30 had greatly reduced harvest index, tillers per m2, and total N uptake but higher grain protein content. There was no significant effect of N topdressing rate on grain yield, although provided the crop was cut before GS 30, higher rates of N increased maturity biomass and crop N uptake by replacing N removed in cut biomass. This study showed that physiological delay of wheat due to cutting was not significant. The forage harvested from winter wheat before stem elongation could be a valuable feed resource to fill the feed gap in western China.

Nitrogen rate and plant density effects on yield and late-season leaf senescence of cotton raised on a saline field

Plant density and nitrogen fertilization are two important practices for field-grown cotton ( Gossypium hirsutum L.). The objective of this study was to investigate the effects of plant density and N fertilization rate, especially their interactions, on yield, yield components, late-season leaf senescence and Cry1Ac expression in Bt ( Bacillus thuringiensis) cotton under salinity conditions. To achieve this goal, we conducted a three-year experiment with a high-yielding Bt cotton cultivar (SCRC 28) in a moderately saline (ECe = 11 dS/m) field, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to low, medium and high plant densities (3.0, 5.25 and 7.5 plants/m 2), while low, moderate and high nitrogen rates (120, 225 and 300 kg N/ha) were assigned to the subplots. Biological yield, lint yield, yield components, harvest index, boll load, Cry1Ac expression and leaf senescence were significantly affected by plant density and N rate. Lint yield was also affected by plant density × N rate interaction. Increased plant density or N rate enhanced biological yield, but reduced harvest index. Considerably high lint yield (1604 kg/ha) was achieved only with a high dose of N fertilizer under low plant density, but comparable yields (1693 and 1643 kg/ha) were achieved with moderate and low N rate under medium and high plant density. Increased plant density and N rate reduced boll load, which had highly significant negative correlation with late-season leaf photosynthesis ( r = −0.928) and significant correlation with Cry1Ac protein concentration ( r = −0.8131). Leaf senescence was delayed by increasing plant density and N rate mainly due to reduced boll load and a combination of reduced boll load and nutritional effect. Medium plant density with moderate N rate or high plant density with low N rate would enhance cotton yield and moderate Cry1Ac expression at reduced cost in the Yellow River Delta of China and other areas with similar ecologies.

Effects of Water Deficit Stress on Several Quantitative and Qualitative Characteristics of Canola (Brassica napus L.) Cultivars

Water deficit stress considered as one of the most important limiting factors for oil seed canola (Brassica napus L.) growth and productivity in Iran. To evaluate the effects of water deficit stress on some qualitative and quantitative characteristics of canola cultivars, this experiment in a greenhouse trial carried out as factorial based on completely randomized design with three replications in Shahid Chamran University of Ahwaz (Iran). Canola cultivars, including ‘Hyola 308’, ‘Hyola 401’ and ‘RGS 003’ as first factor, and the second one was three levels of water deficit stress, including stress at early stem elongation stage to early flowering (D1), early flowering stage to early emergence of sacs (D2), beginning of stem elongation stage to early emergence of sacs (D3) and normal irrigation (C, as check). Results showed that the interaction between water deficit stress and cultivars affected biological yield, seed oil yields and harvest index (p≤0.01), dry matter and economic yield (p≤0.05). Water deficit stress reduced grain oil yields. ‘Hyola 308’ under stress at beginning stem elongation stage to early flowering had the lowest oil yields (1.1 g plants-1) and ‘Hyola 401’ under non-stress conditions showed highest oil yields (4.3 g plants-1). The decrease of oil yields at the flowering stage to stem elongation stage was more than the other stages. In addition, water deficit stress reduced harvest index in the three stress levels due to reduced economic yield and reduced biological yield. Stress susceptibility index for ‘Hyola 401’ at the beginning of stem elongation stage to early emergence of sacs was 0.914 and the ‘Hyola 308’ showed 1.12 at the beginning of stem elongation stage to early emergence of sacs respectively, which it can implies that ‘Hyola 308’ is more sensitive than ‘Hyola 401’ to water deficit stress.

Effect of water stress at different periods on seed yield and water use efficiency of guar under Shambat conditions

Water stress effects on seed yield and water use efficiency of three indeterminate guar (Cyamopsis tetragonoloba L. Taub.) lines (L12, L18 and L33) were investigated in the experimental farm of the Faculty of Agriculture, University of Khartoum for two seasons (2005 and 2006). The guar lines were subjected to water stress induced by withholding irrigation for three weeks. Three water stress treatments were imposed 35, 50 and 65 days after sowing (DAS), and a control treatment irrigated every two weeks. The treatments were arranged in a split-plot design with three replications; with water regime treatments assigned to the main plots and guar lines to the subplots. Data were recorded on seed yield (t.ha–1), number of pods per plant, 1000- seed weight (g), harvest index (HI) and water use efficiency at harvest. The results indicated that exposure of several cultivars of guar to water stress at the three stages of growth didn’t induce any significant effect on number of pods per plant, 1000-seed weight, seed yield and water use efficiency (WUE). On the other hand there was significant reduction in harvest index as a result of imposition of water stress at 35 and 50 DAS. It was also evident that plants re-watered after the stress recovered and had the same values as the control treatment.

Durum wheat (Triticum durum Desf.) in rotation with faba bean (Vicia faba var. minor L.): long-term simulation case study

The aim of this work was to apply the CropSyst simulation model to evaluate the effect of faba bean cultivation as a break crop in the continuous durum wheat cropping system in southern Italy. The model was previously calibrated and validated for durum wheat and faba bean on data derived from experiments carried out in southern Italy (for different years and treatments), comparing observed and simulated crop growth, yield, soil water, and nitrogen output variables. The validation showed good agreement between simulated and observed values for cumulative above-ground biomass, green area index, and soil water content for both crops and grain yield for durum wheat; a negative correlation for grain yield in faba bean was observed due to a reduction in harvest index in the well-watered crop, which the model does not simulate well. Subsequently, a long-term analysis was carried out to study the effects on durum wheat of introducing a legume crop in rotation with the cereal in 2 and 3-year sequences. A long-term simulation, based on 53 years of daily measured weather data, showed that faba bean, due to a lower level of transpirated water (on average 247 mm for durum wheat and 197 mm for faba bean), allowed for greater soil water availability at durum wheat sowing for the cereal when in rotation with a legume crop (on average, +84 mm/m for durum wheat following the faba bean), with positive effects for nitrogen uptake, above-ground biomass, and grain yield of wheat. The yield increase of wheat when following a faba bean crop was on average +12%, but this effect was amplified in drier years (up to 135%). In conclusion, the case study offered the potential to confirm the positive results previously obtained in long/medium-term field experiments on the introduction of faba bean in rotation with durum wheat, as well as reduction in the chemical application of nitrogen.