Weed regimes in agro-ecosystems in the changing climate scenario–A review

Changes in temperature, and the amount, intensity, frequency, and distribution of rainfall, collectively known as climate change, can have beneficial or adverse effects on weeds interfering with agriculture. Implicit in discussion of weed management and climate change is the assumption that we know what to do in relation to soil and crop management, but these strategies might not apply to the unexpected future climate change conditions, particularly weed menace. There is confusion in interpreting weed management for the weather fluctuation in a region, as there is a clear-cut distinction between climate change and climate variability. Soil warming could enhance the availability of certain elements in the soil by faster ion-diffusion rate and the soil-moisture stress could boom weed proliferation. Judicious agronomic practices would partially help to offset weed pressure, but climate may have over-riding influence on weeds, as they share the same trophic level with crops. Implications of climate change would be identical with crops, aggravating the crop-weed competition. Many of the most troublesome weeds in crop ecosystems follow C pathway. As atmospheric CO increases, it is conceivable that competitive ability of weeds could be similar to C crops, such as rice, if there is no dearth of soil moisture and nutrients. From a weed-management perspective, C weeds would flourish under the increased temperature scenario and pose serious yield limitation. It is speculated that reduced water availability due to recurrent/unforeseen droughts would alter the competitive balance between crops and some weed species, intensifying the crop-weed competition pressure. Research conducted indicated that a rise in temperature would benefit C weeds but not the rising CO levels

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Not Availablefield experiment was conducted at College of Agriculture, Odisha University of Agriculture and Technology, Bhubaneswar on sandy loam soils during summer season of 2019 to study the effect of varied nutrient doses and tillage on the nutrient uptake and economics of sunflower (Helianthus annuus L.) hybrids under lowland rice fallow environments. Three sunflower hybrids viz., DRSH-1, KBSH-44 and MSFH-17 were tested under three graded fertility levels RDF (recommended dose of fertilizers), 50% RDF (30: 40: 30 kg N: P2O5: K2O /ha), 100% RDF (60: 80: 60 kg N: P2O5: K2O /ha) and 150% RDF (90:120:90 kg N: P2O5: K2O/ha) and four tillage practices viz., reduced, minimum, zero tillage and conventional tillage practice. Sunflower under zero tillage recorded the highest uptake of N (52.65 kg /ha), P (21.87 kg/ha) and K (76.03 kg/ha) besides highest seed yield (1.91 t/ha). On the other hand, conventional tillage recorded the highest post-harvest soil available nitrogen (216.6 kg /ha), phosphorous (12.9 kg/ha) and potassium (214.4 kg/ha). Among the hybrids, KBSH-44 recorded significantly higher seed yield (1.81 t/ha) besides highest nutrient uptake. Raising sunflower hybrid KBSH-44 under rice fallow zero tillage conditions and fertilized with 150% RDF (90:120:90 kg N: P2O5: K2O/ha) was found economically superior in terms of gross returns, net returns and B: C ratio (2.34).Not Availabl

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Not AvailableIt is concluded that rice fallow sesame needs soil disturbance either in the form of reduced or conventional tillage with aminimum of 50% recommended doseof fertilizer forincreasing the sesame productivity. However, neither the tillage practices, nor the fertilizer doses, havebeen enough against a low productivity of rice fallow sesame and additional research is necessary to manage the soil physical properties to build the rice fallow sesame crop.Not Availabl

Weeds in a Changing Climate: Vulnerabilities, Consequences, and Implications for Future Weed Management

Whilst it is agreed that climate change will impact on the long-term interactions between crops and weeds, the results of this impact are far from clear. We suggest that a thorough understanding of weed dominance and weed interactions, depending on crop and weed ecosystems and crop sequences in the ecosystem, will be the key determining factor for successful weed management. Indeed, we claim that recent changes observed throughout the world within the weed spectrum in different cropping systems which were ostensibly related to climate change, warrant a deeper examination of weed vulnerabilities before a full understanding is reached. For example, the uncontrolled establishment of weeds in crops leads to a mixed population, in terms of C3 and C4 pathways, and this poses a considerable level of complexity for weed management. There is a need to include all possible combinations of crops and weeds while studying the impact of climate change on crop-weed competitive interactions, since, from a weed management perspective, C4 weeds would flourish in the increased temperature scenario and pose serious yield penalties. This is particularly alarming as a majority of the most competitive weeds are C4 plants. Although CO2 is considered as a main contributing factor for climate change, a few Australian studies have also predicted differing responses of weed species due to shifts in rainfall patterns. Reduced water availability, due to recurrent and unforeseen droughts, would alter the competitive balance between crops and some weed species, intensifying the crop-weed competition pressure. Although it is recognized that the weed pressure associated with climate change is a significant threat to crop production, either through increased temperatures, rainfall shift, and elevated CO2 levels, the current knowledge of this effect is very sparse. A few models that have attempted to predict these interactions are discussed in this paper, since these models could play an integral role in developing future management programs for future weed threats. This review has presented a comprehensive discussion of the recent research in this area, and has identified key deficiencies which need further research in crop-weed eco-systems to formulate suitable control measures before the real impacts of climate change set in. © 2017 Ramesh, Matloob, Aslam, Florentine and Chauhan

Analysing the SPAD dynamics of water-stressed vs. well-watered sesame (Sesamum indicum L.) accessions and establishing their relationship with seed yield

Background The chlorophyll content is susceptible to deficit moisture stress and may affect the plant yield. Leaf chlorophyll content is directly related to tolerance and higher productivity under deficit moisture stress (WS). The SPAD meter is an excellent tool for rapid analysis of crop chlorophyll content. Therefore, establishing a relationship between leaf chlorophyll content and seed yield is crucial in sesame, particularly under deficit moisture stress. Methods Seeds of 37 sesame genotypes with checks were used in this study. These genotypes were mostly landraces, adapted to different agro-ecological zones in India. The selected genotypes were evaluated under well water (WW) and deficit moisture stress (WS) conditions. The SPAD readings were recorded ten (10) times each at every seven days intervals from the juvenile/first bud (30–35 days after sowing) to ripening/ physiological maturity (95–100 days after sowing) stage. This study aimed to identify the association between leaf SPAD readings (recorded at 7-days interval) and seed yield of sesame genotypes. Results The analysis of variance revealed the presence of significant variation in SPAD readings due to treatment (WW and WS), genotypes, and their interaction effects. The SPAD readings at all stages were positively correlated with seed yield in both WW and WS. High values of correlation coefficients were observed at 52 (r: 0.672) and 59 (r: 0.655) DAS under WS; whereas at 59 (r: 0.960), 66 (r: 0.972) and 73 (r: 0.974) DAS under WW at one percent significance level (p < 0.01), which coincided with the mid-bloom stage of the sesame crop. The best-fit multiple regression model revealed that the dependence of sesame seed yield is significantly influenced by SPAD reading at 52 DAS under WS and 59 to 73 DAS under WW. Both these models provide a good fit with the chi-squared test, which compares the predicted and observed yield

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Not AvailablePotassium (K) is the most neglected nutrient in Indian agriculture and accounts only 10% of the total fertilizer use. The increased cropping intensity and use of high yielding cultivars since the green revolution led to heavy withdrawal of K from soil. Persistent K mining over the past six decades has mined soil K level in many cultivated areas and continuously transforming sufficiency into deficiency. A recent soil test a little over 1 lakh samples from 33 states of India have categorized 41.1%, 29.3%, and 29.5% of soil samples as low, medium and high in available K respectively. Further, the trend of soil available K status showed a persistent decline in percentage of area under high and medium soil K. Consequently, the evidence of rice crop responding to K nutrition is increased. This review attempts the nexus of K nutrition in rice for devising strategies for potassium management in rice-based cropping systems in the countryNot Availabl