Tag: macetas para viveros

Weather has often been seen as the ideal exogenous right-hand side variable

The bounty of plenty, in the twenty-first century, is questioned not due to its productive capabilities but rather because of its lack of a palatable narrative of place and transparency to which it could inform, and reassure, its consumers and citizens. This conundrum is eloquently summed up by Connerton : “As natural ecosystems became more intimately linked to the urban marketplace of Chicago, they came to appear ever more remote from the busy place that was Chicago. Chicago both fostered an ever-closer connection between city and country, and concealed the very linkages it was creating.” Problems and issues associated with modern agricultural production, for instance is to a large degree perceptual. This is not to say that these developments are not indeed real, but that the ultimately overall meanings and thus societal importance and individual significance rest, to a large degree, in the perceptions of such developments and their perceived effects, as one cannot know everything for sure, and even what sure, or the truth, means might be debatable as we move from “Authority to Authenticity” . Perceptions about agriculture, food and people, therefore, does not just serve to navigate, interpret and/or internalize the symbols imposed by other agents and structures, but also, in their appropriation, circumvents and re-invents meanings and understandings of these. In other words, the importance of perceptions lies both in their use as “interpreters” of the surrounding world and as creators of the surroundings – the change perspective. These must, surely, not be underestimated, as is evident in the burgeoning food movements and its spatial outlets,precio de macetas de plastico as well as the increasing organic production worldwide. Also, important is the fact that participation in the local sphere is for many in the Western World a choice made out of want and less so out of social and economic necessity as in the past – perhaps reflected in an increase in informalization .

This “choice,” it should be noted still, often, excludes and eludes people with low socio-economic status, who still depend very much on locality, as their mobility and often also skills are more limited and less “mobile.” Context continues to matter, greatly, if for different reasons, and with different effects, than in yesteryears. Lastly, I would like to add that this paper is not a rebuff of the criticism levelled at the food markets and its actors in regards to its, at times, exploitative attitudes towards the nature of resources , workers governance and politics , among others. It is rather an attempt to show how these held perceptions came about, and how structural and historical developments can contribute to explaining their emergence, without retorting to complete structural determinism or complete rational-choice “free” actor perspectives, the two preferred methodological and philosophical lenses that the oppositional camps of these issues wear. Rather, reality is formed by perceptions that both influence and are influenced by individual choices and structural developments, whose autonomy and power structures vary depending on context. There is mounting evidence that the global climate has already changed and it is projected to continue changing for the coming centuries . The world has experienced many new record highs that suggest that the mean temperature is increasing. For example, Munasinghe et al. examine the frequency of new record temperatures across the global landmass and find that the frequency of extremely high temperatures increased tenfold between the beginning of the 20th century and 1999–2008, the most recent decade for which they obtained gridded weather data. At the same time, the frequency of new record lows has also increased, suggesting that the variance and not only the mean may have increased. A spatially disaggregate analysis reveals that the tropics experienced a larger increase in the frequency of record highs during the last 100 years than higher latitudes. This is consistent with forecasts of global circulation models . Looking across 23 circulation models, the authors find that countries in the tropics have a probability greater than 90% of experiencing average summer temperatures by the end of the 21st century that are larger than the hottest summers on record in 1900–2006.

In higher latitudes, the average seasonal temperature will be about equal to the hottest on record for the period 1900–2006. On the other hand, Hsiang and Parshall plot the distribution of absolute changes in predicted temperatures for a number of global circulation models and emphasize that the higher latitudes have larger predicted increases in temperature. While this might at first seem like a contradiction, the reason for this finding is that there is less historic variation in the tropics than in the higher latitudes, and more of the increased warming in the higher latitudes will occur during the winter time. The key features of observed trends as well as future warming are the observed and predicted non-uniformity of warming as well as sharp increase in record highs, especially in lower latitudes that generally have less institutional capacity to adapt to these new records. The predicted change in the mean and variance of weather has direct implications for agriculture, since weather is a direct input into the production function. Unlike many other sectors of the economy that are shielded from weather fluctuations through buildings, agriculture is still at the direct mercy of weather fluctuations . As we will discuss below, the relationship between yields and weather is highly nonlinear and concave. The best predictor of corn yields is a measure of extreme heat over the growing season that only incorporates temperature above29 °C , and slightly higher thresholds apply to soybeans and cotton. Future impacts crucially depend on how often and by how much this threshold will be passed, which can both occur due to an increase in the mean or the variance. As Munasinghe et al. have shown, the observed trend is fairly large. It is generally easier to adapt to shifts in the mean than to shifts in the variance, as optimal crop varieties have to be chosen and planted before the unknown weather is realized. An anticipated change in the mean can be incorporated at the time the planting decision is made, while a change in the variance increases the uncertainty of what will happen after the crop is planted.

Adequate adaptation to an increase in the variance hence has to allow for flexible adjustments during the growing season, e.g., the construction of irrigation systems that can counterbalance fluctuations in temperatures, which increase water demands, as well as fluctuations in precipitation. The majority of studies so far have examined the effects of changes in the mean climate, while estimates of the effects of an increase in the variance are just starting to emerge. It is therefore paramount that empirical studies as well as integrated assessment models move away from impact evaluations that only look at changes in average global temperature or rely on a single global circulation model . Further, reliance on average temperature in these modeling exercises does not properly capture the spatial and seasonal heterogeneity in predicted temperature changes. This reasoning carries over to predicted changes in precipitation, for which there is much less agreement across models. There is a myriad of studies examining the effect of weather/climate on agriculture, both structural integrated assessment models and reduced-form empirical studies. Chetty sees the advantages of reduced-form strategies in “transparent and credible identification”, while the important advantage of structural models is “the ability to make predictions about counterfactual outcomes and welfare.” This paper discusses the issues involved in identifying the impact of climate change on agriculture both on the intensive and extensive margins. We put a special focus on the role of extreme temperatures. Hertel and Lobell in this issue discuss the literature on structural modeling approaches for this important sector. The paper is not meant to be a universal overview of the literature,macetas para viveros but as a survey of issues facing empirical researchers interested in identifying impacts in this important coupled human/natural system. The remainder of our paper is organized as follows. Section 2 summarizes the issues involved in identifying the impact of climate/ weather on agriculture, emphasizing the importance of extreme weather outcomes. Section 3 discusses issues involved in identifying evidence of adaptation in the agricultural sector. Section 4 concludes.There is a long history of empirical estimates of the effect of weather on agricultural outcomes. For example, Fisher developed the concept of maximum likelihood estimation by linking wheat yields to precipitation outcomes.Weather impacts agricultural outcomes, yet humans traditionally have not been able to influence year-to-year weather fluctuations. Only recently have cloud seeding experiments been used to influence precipitation. While it is impossible to summarize the entire history of empirical studies, we focus our attention to the most recent studies. Advances in computer power and data availability have made it possible to fit models with a huge number of observations, which allow for the identification and estimation of a more flexible relationship between weather variables and agricultural outcomes.

One of the most important differentiating factors between econometric studies is the source of variation the study uses to link agricultural outcomes to weather/climate: one has to either rely on time series variation, cross-sectional variation, or a combination of the two in a panel setting. Each source of identifying variation will be discussed in turn. Agronomic field experiments have linked agricultural outcomes to various weather measures in both controlled laboratory settings as well as real-world settings that rely on farm-level data. The number of plots or parcels has traditionally been very limited. For example, McIntosh outlines how time-series variation over two or more field experiments can be combined in a statistical setting. Such field experiments have been used to examine not only the effects of weather variables, but more generally of all sort of inputs, including fertilizer, CO2 concentrations, etc. The estimated weather parameters have been used to predict the effects of changes in climate. This approach has been criticized as “dumb farmer” scenario, as it implicitly assumes that farmers continue to grow the same crop even if the climate is permanently altered. One extension is hence to derive predicted yields under various climate change scenarios and then model the effect of inputs, crop choice, and prices . In their seminal paper, Mendelsohn et al. use a cross sectional analysis that links county-level farmland values in the United State to climatic variables as well as other controls . The advantage of the cross-sectional approach is that farmers in different climatic zones had time to adjust their production system to different climates. For example, if it were to become permanently warmer in Iowa, farmers could adjust their production systems to cope with the hotter climate, just as farmers in Florida have done in the past. Florida farmers currently face higher average temperatures than farmers in Iowa, and hence might be a good case study of how farmers will adapt. There are, however, at least three significant drawbacks to cross sectional studies of this type. First, any cross-sectional analysis is subject to omitted variable bias, as statistical correlations do not imply causation. For example, Schlenker et al. show that access to highly subsidized irrigation water is positively correlated with hotter temperatures. The benefits of higher temperatures in a cross-sectional analysis are upward biased as they also include the beneficial effect of access to subsidized irrigation water. Second, Timmins shows that within-county heterogeneity and endogenous land use decisions can bias Ricardian analyses by allowing for use-specific error terms in his cross-sectional analysis of county-level Brazilian farmland values. Farmers endogenously select the crop they are best suited to grow. The effect of climate on land values hence depends both on how a particular land use responds to climatic conditions, as well as what land use is selected as a function of climate. Third, traditional cross-sectional analyses of farmland values are partial-equilibrium studies. If weather were to make farming either greatly more or less productive, prices for agricultural goods would adjust, and so would farmland values. This is evident in the recent sharp increase in commodity prices that led to a significant increase in the US farmland values. Consumer surplus decreased while producer surplus increased. A decrease in farm productivity might in some circumstance even be good for farmers as demand for agricultural products is highly inelastic and weather-induced yield reductions increase the price of agricultural commodities.

The solids were then quickly centrifuged and excess solvent was decanted to avoid moisture uptake

Dry trehalose was then added and completely dissolved. Finally, 4- vinylbenzyl chloride was added dropwise. The reaction was stirred for 22 hours at 22 °C. The reaction mixture was then precipitated into a rapidly stirring solution of methylene chloride and hexanes . The solids were collected by vacuum filtration through a sintered glass funnel equipped with a filter flask.Solvents were further removed in vacuo over 10 hours and then solids were broken up with a spatula to increase surface area and make drying more efficient. The solids were dried for an additional 24 hours before being used for gelation without further purification. To synthesize the gels, the crude trehalose monomer and cross-linker mixture was completely dissolved in Milli Q water . To this, tetramethylethylenediamine was added. This mixture and a 10 mg mL-1 stock solution of ammonium persulfate in Milli Q water were separately degassed for 30 minutes by sparging with argon. Under an inert atmosphere of argon gas, the APS solution was added to the crude styrenyl-trehalose solids and TEMED for a final ratio of 1 g crude material for every 1 mL Milli Q water, 5 µL TEMED, and 250 µL APS solution . The solution was gently shaken for 12 hours to form a gel. The crude gel was washed with a Soxhlet extractor for three days with deionized water to removed unreacted monomers, crosslinkers, and other impurities,fabrica de macetas plasticas providing a clear gel. The yields of gelations were based on comparing the moles of limiting reagent, 4-vinylbenzyl chloride, to the moles of final product.

The final product molecular weight was calculated based on the molecular weights of each of the individual components of the crude mixture, and the distribution of these products was determined by LCMS . Finally, the gel was lyophilized and then ground to produce a fine, white powder. The overall yield of the two-step synthesis was 87.5%, providing 155.9 mg of gel. The synthesis was increased 100-fold and carried out as outlined above with the following exceptions: the monomer/cross-linker reaction was stirred for 46 hours instead of 22 hours as a longer reaction time was required to have sufficient styrene-functionalization on trehalose, the reaction was then precipitated in 100 mL aliquots into DCM and hexanes at an approximate rate of 150 mL per minute while the suspension stirred at 800 rpm, and the final crude gel was washed for 7 days with deionized water in a Soxhlet extractor. The reaction gave an overall yield of 75.6%, providing 81.02 g of monomer/cross linker and 13.8 g of gel. Gelation was confirmed by examining physical properties of the gels, e.g. storage and loss modulus as well as swelling ratio. Storage and loss modulus were measured by trimming hydrogels to 8-mm diameters to match the top parallel plate geometry and with an applied constant strain of 1% and angular frequency range of 0.1 to 10 rad/s at 22 °C. Swelling ratio was determined by swelling completely dried hydrogels in Milli Q water over 72 hours and calculating the mass ratio between the swollen gels and their initial dry weights. All physical properties are displayed as the average and standard deviations of three independent hydrogel measurements.Phytase activity was measured by modifying a previously reported method.Phytase stock solution was added to trehalose gels and prepared as described above. Heated and control hydrogels were removed by centrifugation after addition of sodium acetate buffer and incubation.

Supernatant was added to 1 mL of 0.2 M sodium citrate buffer, pH 5.5. Aliquots were transferred to Lobind Eppendorf tubes. To all sample tubes, 10 µL of 1% phytic acid was added. The reactions were then incubated at 37 °C for 15 minutes before quenching with 15% trichloroacetic acid and then diluted ten-fold with Milli Q water . Aliquots were transferred to a 96-well plate and then diluted with a 1:3:1 solution of 2.5% ammonium molybdate , 10% sulfuric acid , and 10% ascorbic acid . The plate was covered with parafilm and then incubated at 50 °C in a water bath for 15 minutes, cooled at 4 °C for 15 minutes, and absorbance measurements were taken at 820 nm. Phytase activity was defined as the quantity of enzyme that catalyzes the liberation of 1.0 µmol of inorganic phosphate from 1 % phytic acid per minute at 37 °C and pH 5.5. Assay was run in triplicate. Note that generally this assay is difficult to reproduce due to the fast reaction between phytase and phytic acid. We advise that the assay be done as quickly as possible, using a multi-pipetter.Stock solution of b-glucanase was added to trehalose gels and prepared as described above. Heated and control hydrogels were centrifuged after addition of sodium acetate buffer and incubation. Supernatant was pre-warmed along with azoBarley glucan substrate provided in Megazyme assay kit at 30 °C for five minutes. Due to the viscous nature of the glucan substrate, it was transferred using a positive displacement pipet. Aliquots of the supernatant was added to azo-Barley glucan substrate and then mixed vigorously before incubating at 30 °C for 10 minutes. Precipitation solution was made by dissolving sodium acetate and zinc acetate in distilled water . The pH was then adjusted to 5.0 with concentrated hydrochloric acid, and the volume was adjusted to 200.0 mL. Finally, 2-methoxyethanol was added. An aliquot of this precipitation solution was added to each sample, and the contents were mixed vigorously, incubated at ambient conditions for five minutes, and then mixed vigorously again.

Finally, the samples were centrifuged at 6,000 rpm for 10 minutes, supernatant was added to a 96-well plate, and the absorbance was read at 590 nm. b-Glucanase activity was defined as the quantity of enzyme that catalyzes the liberation of 1.0 µmol of glucose reducing sugar equivalent from azo-Barley glucan substrate per minute at 37 °C and pH 4.6. Experiments were repeated in triplicate.Note that all LB media used throughout these studies contained 50 µg/mL kanamycin to prevent other strains of bacteria from growing. A colony of kanamycin-resistant strain of BL21 E. Coli bacteria was grown in 50 mL LB media in a 250 mL sterilized Erlenmeyer flask at 37 °C and 200 rpm. At an OD600 of 0.426, the bacteria was diluted in 50 mL LB media and incubated at 37 °C and 200 rpm for an additional 1.5 hours. The bacteria was diluted 1:1 in LB media containing P3, free trehalose or no excipient . The samples were frozen and lyophilized for 24 hours. Following lyophilization stress, 200 µL of LB media was added to each condition. Aliquots of 150 µL were added to 3 mL of fresh LB media in culture tubes and incubated at 37 °C and 200 rpm. Cell growth was monitored by measuring the absorbance at 600 nm.As drought frequency, severity, and duration are exacerbated by climate change,improving the efficiency of water resources is crucial for a sustainable future. Drought affects agriculture globally and poorly affects food security, water availability, and rural livelihoods. In the developing world alone, drought caused $29 billion agriculture revenue loss between 2005 and 2015.Drought cannot be avoided, but mitigation practices can negate its deleterious effects. In particular, drought reduces crop productivity due to high temperatures and limited water,but on-farm water and soil management have proven successful in abating these issues. Despite this, many inefficient practices, such as flood irrigation, are still widely applied.Technologies that prevent agricultural water wastage must be developed and implemented to improve the health of crops subjected to drought. Hydrogels are hydrophilic polymeric materials capable of absorbing and releasing water many times their weight.In soil, swollen hydrogels act as water reservoirs by slowly releasing captured water through a diffusion-driven mechanism that arises from humidity variation between the internal environment of the material and the soil surrounding it. Hydrogels have been mixed into soil to prevent water irrigation loss caused by drainage and evaporation. They also offer a potential scaffold for controlled release of nutrients,and provide better oxygenation to plant roots by increasing soil porosity. By improving the water holding capacity of soil and water available to plant roots, hydrogels have demonstrated the ability to increase plant survival rate, water use efficiency, and growth.While superabsorbent polyacrylate gels have demonstrated success as soil conditioners,precio de macetas de plastico it is hypothesized that anionic moieties within hydrogels create electrostatic repulsions with negative charges on the surface of soil particles.The anion-anion repulsive forces can reduce adsorption of the hydrogel to soil and therefore allow the polymer to be leached by water over time. The development of alternative hydrophilic gels for soil conditioning could help overcome these issues and potentially demonstrate other advantages. The Maynard lab has designed a scalable, two-step synthesis of a trehalose-based hydrogel for the thermal stabilization of enzymes.The synthesis yield was greatly improved from 17 % to 88 %, scaled 100-fold while retaining a high yield at 76 %, and was optimized to eliminate the use of halogenated and toxic solvents .

This multi-gram, green synthesis makes the gel more practical for agricultural applications where materials need to be cost-efficient and scalable.20 Moreover, trehalose has been shown to stabilize desiccant-intolerant soil bacteria necessary for plant growth.As such, trehalose hydrogels have great potential for water management as well as stabilization and delivery of plant nutrients while being beneficial to soil. Here, two hydrogels, a commercially available poly-based gel, Terra-sorb , and a trehalose hydrogel, synthesized by our lab as described in Chapter 2, were separately applied as soil amendments for tomato plants, Solanum lycopersicum, subjected to drought conditions. Performance of the gels was evaluated by monitoring tomato plant health through chlorophyll content, water potential, stomatal conductance, and relative growth rate measurements. We hypothesized that presence of the trehalose hydrogel would boost tomato plants’ physiological function after extended droughts . We also hypothesized that since the trehalosehydrogels were less hydrophilic than the Terra-sorb hydrogels, they would likely not be as efficacious as the positive control.Due to climate change, water availability has become more sporadic with cycles of drought and rewatering, which ultimately stresses plants.We therefore tested the ability for the hydrogels to retain their swelling ratio through repeated drying and wetting cycles. After purification and lyophilization, the trehalose hydrogels were swollen to their maximum capacity in 72 hours in deionized water. This drying-swelling cycle was repeated where the dry weight was taken after lyophilization and swollen weight was taken after swelling the gel in deionized water. The swelling ratio was calculated for each cycle by dividing the difference between the gels’ swollen weight and dry weight by the dry weight . Over the course of ten drying-swelling cycles , the hydrogels swelling ratio decreased from 16.3 ± 2.9 to 14.9 ± 1.1 . This minimal loss in swelling ratio during these cycles is an indicator that the gel could be subjected to multiple drought cycles without compromising its swelling abilities. Next, we evaluated how the water holding capacity of a sandy loam soil is affected by Terra-sorb and the trehalose hydrogel. We applied Terra-sorb at the manufacture’s recommended concentration, 0.4 wt %, and trehalose hydrogel at 0.4 wt % and 0.8 wt % . We saturated the soil then allowed it to desaturate over eight days while monitoring water loss by weight. All of the amendments improved the water holding capacity of the soil over the entirety of the experiment. Consistently, soil amended with Terra-sorb gels had the highest WHC, followed by soil with trehalose hydrogel at 0.8 wt % and then 0.4 wt %. We then rehydrated the soils to evaluate the gels’ capacities to work through multiple drying cycles. The conditioners maintained their previous trends and most of their WHC percentages. While WHC is an important factor for soil health, the water held by hydrogels is not necessarily available to crops.As such, it is vital to monitor plant growth in soil with the hydrogel amendments.Previous reports have demonstrated that hydrogel soil conditioners are not always effective in improving plant health and growth, and, in fact, are sometimes detrimental, depending on the soil type, plant species, and experimental conditions.So, before testing trehalose hydrogels directly, we ensured that tomato plants and our simulated drought conditions could benefit from soil conditioners by using commercially available hydrogel, Terra-sorb at 0.4 wt %, that has previously demonstrated delayed moisture loss for Quercus ruba seedlings subjected to short-term desiccation stress.