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The model includes a non-linear term for investments in infrastructure

The remainder of the paper is organized as follows: Section 2 reviews previous works and places our paper within that literature. Section 3 develops the econometric methodology, departing from the previous published work on agricultural knowledge that is reviewed in Section 2. Section 4 describes the data and variable creation. Section 4 reports the empirical results, and Section 5 presents the conclusion and policy implications.The knowledge production function has various applications at societal and sectoral levels. A recent published theoretical framework addressing the role of knowledge in society’s growth was developed by Dolgonosov . Distinguishing between technological knowledge and general total knowledge, the author demonstrated that knowledge is essential to allow sustainable population growth within the carrying capacity of the planet. The role of knowledge production is essential, especially with the increasing population and environmental load. This framework suggests that society could introduce policies to improve the efficiency of knowledge production in various sectors. The literature distinguishes also between knowledge of various qualities. Cammarano et al. introduced the notion of quality of innovation output, using patent data from bio-pharmaceutical and equipment-producing companies. The analysis suggests a more productive knowledge process in which innovative firms use knowledge and information produced by external sources. Working on a related industry, Lauto and Valentin estimated a knowledge production function for what was coined the new science development model for clinical medicine,hydroponic dutch buckets in which research can be conducted in a transnational effort, or locally.

This is a very interesting distinction that may indicate the efficiency of transnational simultaneous research benefitting from a variety of conditions and its superiority to knowledge spillover of research conducted separately. However, the authors find that by its nature, transnational research may have lower efficiency and impact because it includes diverse aspects in quantitative comparisons. Some surprising findings are offered by Roper and Hewitt-Dundas , who estimates the interaction between knowledge stocks and flows and their impact on the firm’s innovation. They found that negative rather than positive effects between knowledge stocks and innovation , and knowledge flows dominate the effects of knowledge stocks on the innovation of the firm. Several works address the issue of networking and proximity among the knowledge creation centers , and the effects of collaboration within and between regions on knowledge productivity . Both works were applied to Europe. Ramani et al. develop a model of knowledge production function that can be estimated at both the firm and the sector level and apply it to the bio-food industry. The production function in this work allows to distinguish between the absorptive capacity to exploit inter- and intrasectoral spillovers. Marrocu et al. found that technological proximity outperforms the geographic proximity, suggesting that networking has a limited role in enhancing knowledge creation. The most relevant finding of De Noni et al. to our work is that the impact on knowledge productivity is stronger in the case of collaboration between regions with diversified knowledge base. From a different perspective, Verspagen and De Loo addressed the spillover effect of knowledge, both across sectors and over time using a knowledge flow matrix. The methodology is very relevant for knowledge production investments, but it is heavily dependent on data that might not be readily available everywhere. Two examples of recent studies that address spillover effects in knowledge production are Wang et al. and Neves and Sequeira . Wang et al. estimated the spillover effects in the semiconductor industry to find that the strength of the networking ties between companies explain the level of spillover effect in the knowledge production process. Spillover effects are expected to be stronger in weaker network ties. Neves and Sequeira conducted a meta-analysis of data from 15 published works to find expected, but reassuring results.

They quantify level of spillover effects and discover that the spillover effect will be larger when they include in the estimation of the knowledge production foreign inputs, and it will be lower when only rich economics are included in the estimation. Finally, universities are considered a hub for knowledge production, based on research conducted in addition to their role as educational institutions. Gurmu et al. used patents issued to universities during 1985–1999 as a measure of knowledge. They explained variation in knowledge by field of knowledge, R&D expenditures , as well as detailed human capital variables, and several control variables. Their results indicated marginal contribution of each research variable to the production of knowledge. While the literature review is by no means inclusive, it represents the many efforts that have been made in the literature for understanding the determinants of knowledge production. We will rely on these works while developing our analytical framework.The literature suggests that agriculture-related R&D inputs result in the production of knowledge, which upon application leads to improvement in productivity in the agricultural sector. Alston et al. , Birkhaeuser et al. , and Evenson estimated the impact of R&D and extension-related expenditures on agricultural productivity. The underlying theory is that expenditures made towards R&D and outreach impact productivity, and that impact of research expenditures is differential; old expenditures have a lower impact on current productivity. Evenson and Birkhaeuser et al. reported positive impacts of both R&D and cooperative extensions on productivity for studies from around the world. While these studies provide strong evidence of a long-term impact of R&D-related expenditure as well as the impact of farmer-extension agent contacts on productivity, there is a gap in our understanding of how well these proxies for agricultural knowledge represent actual knowledge produced. This is understandable because measurement of knowledge produced from investments in R&D is conceptually and computationally complicated. Griliches discussed the issues of measurement of knowledge production between public and private sector investments in R&D. He claimed that patents are a good approximation of knowledge and innovation, especially because of the commercial value attached to it. An industry or a firm likes to file for patents to have sole right on its invention and is paid for its use by others. Pavitt mentioned that patents are good proxy measures of innovative activities. Other studies have used patents as proxies for knowledge production.

Data on patents are well documented in the United States and in the rest of the world and are easily obtainable without the hassle of conversion of units. In the industrial sector, knowledge produced through research is mostly owned as private property by the innovating firm because of the related commercial incentive of private property ownership. This makes patents the most appropriate proxy variable for knowledge production function analysis in the case of private sector research. However, publicly funded research and especially agricultural research creates knowledge, most of which is publicly available. Pardey and Dinar used publications as a proxy for knowledge production. Publications are more prevalent in public research agencies, where research results are typically published in journals. Dinar used peer-reviewed journal publications in different fields as the dependent variable for his study of the agricultural research system in Israel. According to Pardey , publications have been chosen over patented and non-patented output like mechanical innovation processes or new biological material, books, State Agricultural Experiment Station bulletins, and newsletters. Publications capture the knowledge output of a station completely because they establish intellectual property rights of the researchers over their work,bato bucket which in turn affect their salary scale, promotion rate, and tenure status. Link analyzed the determinants of inter-farm differences on the composition of R&D spending, namely basic and applied R&D. He regressed these R&D components on profits, diversification, ownership structure, and subsidies. Jaffe found a significant positive impact of university research on corporate patents for a number of technical areas, such as drugs and medical technology, and electronics, optics and nuclear technology in the United States. The literature on the topic leads us to two main observations: a dearth of papers that deal with the analysis of the knowledge production function and the study of the impact of production inputs on knowledge produced; and the choice of variables representing knowledge produced through investments in R&D only provides a partial picture of the true process. There is little attempt to compute a comprehensive knowledge production variable that captures knowledge produced through all avenues. UCCE follows an input-output framework for research, which involves utilization of research inputs such as manpower and infrastructure, for the production of knowledge to be disseminated to potential clientele from a variety of different sectors. This knowledge is produced through basic and applied research, and extension work, which are targeted to address the needs of the clients at the county level. Agricultural knowledge that is generated by UCCE is public in nature and is freely available to all.

Because of this, it seems appropriate to use various types of peer-reviewed publications by advisors as the representative variable for knowledge. But publications are only a part of the total knowledge produced; there are other modes by which knowledge is produced and disseminated by UCCE. These need to be incorporated into the analysis to capture a more complete representation of the generated knowledge. To achieve this, we collected data on eleven different modes by which UCCE produces knowledge, all of which are aggregated to the county level to create a knowledge index that captures all UCCE knowledge produced.ichotomous variables representing county fixed effects are introduced in the model to control for factors that are common to a county, and possibly impact productivity. Year fixed effects can control for random shocks, e.g., budget surplus leading to a recruitment of more skilled advisors in a particular year, which may have led to larger number of total knowledge produced across all counties in a single year.This is included to capture possible diminishing marginal returns to infrastructure. Expenditure on infrastructure can be beneficial to knowledge production, but after a certain degree of provision the marginal effect may diminish. It makes little sense to keep building laboratories and offices if there are no researchers or staff to fill them. We follow Roper and Hewitt-Dundas , who introduced the plant size as a quadratic Schumpeterian resource indicator, which has also been shown by Jordan and O’Leary to have an inverted-U shaped relationship with knowledge production. A similar specification by Charlot et al. lumps all R&D costs in a quadratic relationship due to economies and diseconomies of scale. The quadratic specification of infrastructure expenses means that over-investment in research infrastructure may turn to be counter-productive and to result in diminishing marginal productivity of knowledge production. To test this hypothesis, the square term for log of infrastructure expenses was included in our model. The choice of the log-log model for the empirical analysis is to facilitate the computation of output elasticity for each of the inputs of production.The University of California Cooperative Extension was established a century ago with the purpose of educating the citizens about agriculture, home economics, mechanical arts and other practical professions.2 Through the course of almost a century since the Smith Lever Act of 1914, the UC Cooperative Extension has grown into an elaborate system that has branched out from handling mainly farm related issues to many other aspects concerning the farm, as well as the overall society. Extension advisors communicate practical research-based knowledge to agricultural producers, small business owners, youth, and consumers, who then adopt and adapt it to improve productivity and income. Today the UCCE works in six major areas,including Agriculture, 4-H Youth Development, Natural Resources, Leadership Development, Family and Consumer Sciences, and Community and Economic Development. This paper focuses on UCCE activities in agriculture. The University of California Division of Agriculture and Natural Resources headquartered in Oakland, California, is the source of data for the analysis in this paper. We collected annual budget data from the database for all UCCE county offices for the period of 2007 to 2013.Our data set includes complete data for seven years for 47 county offices, which serve the 58 counties in California. There are six groups of two counties each, which are served by a single county office. And there is one office that serves four counties. Upon comparing older UCCE budget data with real expenditures, we found that they follow similar time trends for each county office and could be used as proxies for expenditures. This data was converted into constant 2013 US dollars, using GDP deflator data from the World Bank database and is presented as such hereafter.Henceforth, we will refer to the UCCE budget as expenditures, to avoid ambiguity.

The growth in fresh-cut produce is rapidly reshaping the produce sector

As heightened attention has been brought to bear on obesity as a serious national health concern, in conjunction with mounting scientific evidence regarding the health benefits of fresh produce, more governmental effort is now focused on relaying positive messages to consumers about the potential health rewards of fruit and vegetable consumption. For example, there are new federal school lunch program initiatives featuring fruits and vegetables and a revamped USDA Food Guide Pyramid. The benefits of fruits and vegetables are being promoted by the Produce for Better Health Foundation in conjunction with numerous organizations such as the National Cancer Institute. Increasingly, consumer awareness of the benefits of eating fruits, vegetables and nuts is rising. Per capita consumption of fruits and vegetables, in both fresh and processed form, increased 15 percent from 1976 to 2002, reaching 324 kg, as shown in Table 2. However, examining only the total fruit and vegetable category masks important changes occurring within, such as changes in product form and relative preferences for vegetables versus fruits. Health claims benefited fresh fruits and vegetables proportionally more than processed ones, with 59 percent of total fruit and vegetable consumption in fresh form in 2002, compared to 49 percent in 1976. Fresh fruit and vegetable consumption totaled 145 kg in 2002, up 8 percent over 1989 and 29 percent relative to 1976. These gains are impressive in a developed country with a mature food market in the aggregate. Vegetable consumption, in both fresh and processed form,hydroponic channel grew much more rapidly from 1976-02 than did fruit consumption. Vegetable per capita consumption increased 20 percent to 195 kg, while per capita total fruit consumption grew by only 7percent to 128 kg.

Key forces driving the increase in vegetable consumption include the emergence of fresh-cut salads and vegetables , growth in the fast food industry with its usage of processed tomatoes, primarily for pizza, and processed potatoes, primarily for French fries.In 2002 fresh-cut produce sales were estimated to have reached $12.6 billion , with about 60 percent sold via food service channels and the remainder through retail. However, to date primarily vegetables have benefited from this trend. In 2002 the value of fresh-cut fruit sold through supermarket channels was still quite small, $238 million according to IRI, with total sales including through food service channels estimated by industry sources at over $600 million. Recently fresh-cut fruit new-product introductions have risen and fresh cut fruit post harvest technology is improving. Growing consumer demand for convenient, healthy snack foods and desserts lead some to predict that fresh-cut fruit may be poised for the same type of rapid growth experienced by fresh-cut vegetables over the last decade. California fruit shippers should benefit from this growth, both as producers and as sourcing agents. The diversity of fresh produce offerings in U.S. supermarkets has expanded at an astounding rate. The number of items carried by the average supermarket produce department increased from 133 items in 1981 to 350 items in 2001. This reflects the emergence of more diverse eating habits, and the growing demand for specialty and ethnic fresh fruits and vegetables, as well as the introduction of a myriad of fresh-cut, value-added products, designed to respond to the growing consumer demand for convenience. The abundant supply of increasingly diverse and convenient fruit and vegetable offerings should support continued growth in per capita consumption.

Exports have come to represent an increasingly important growth market for U.S. food marketers, in light of a mature domestic market. The importance of the export market varies widely by commodity and state, with a weighted average export share of 18 percent for the top 50 products produced in California in 2002 . Among horticultural crops export shares are higher for nuts than for fruit and vegetables, due to the lower perishability of nuts and California’s important role in world production. Over 60 percent of California’s almond crop is exported annually compared with 10 percent of lettuce and around 12 percent of strawberries. With certain important exceptions California is a net exporter of most of the crops it produces, even those facing import competition. Most fresh produce imports tend to enter during the off- or early-season when domestic production, including in California, is low. Trade liberalization negotiated under the Uruguay Round of the GATT and implemented under the World Trade Organization , as well as through regional trade agreements such as NAFTA, has expanded market access and strengthened mechanisms for combating non-tariff trade barriers such as scientifically unfounded phytosanitary restrictions. Advances in post harvest technology, including the development of container-level modified atmosphere technologies, have also facilitated exporting perishables to distant markets. Total U.S. horticultural exports, including fresh and processed fruits, vegetables, and nuts, were $11.3 billion in 2002, up from $2.7 billion in 1985. California firms captured a sizable share of this export growth, exporting $4.9 billion worth of horticultural products in 2002 according to USDA. However, trade liberalization has also led to greater import demand, with U.S. horticultural imports reaching $18.7 billion in 2002.

In recent years imports have grown more rapidly than exports but imports are still a small share of total U.S. horticultural consumption, 18 percent in 2001. As markets become more open, they become globalized and many California commodity sectors are increasingly impacted by changes occurring in international markets. Expanding export demand, in particular in Asia, led by Japan, in the first half of the 1990s caused producers to increase plantings of perennial fruit crops, for example. By the time this area was coming into production as of around 1995 and beyond, export markets had peaked and declined due to Japan’s economic recession and the resulting Asian flu. A growing export market in Mexico also temporarily peaked in 1995 due to an economic crisis there. Simultaneously, greater world production of many commodities also grown in California has increased competition for California firms in third country markets. The rapid emergence of China as a major producer and growing exporter of fruits and vegetables is already having a competitive impact on demand for California products in Asian markets and will continue to do so as China improves its infrastructure and export quality. China is the world’s largest producer of vegetables, apples and pears. Although most of the production remains in China to serve internal demand generated by its 1.3 billion inhabitants,hydroponic dutch buckets even a small export share can be significant relative to the international volumes normally traded in any given commodity. On the other hand, income growth should expand import demand as Chinese consumers demand a greater array of higher quality food products, including fruits and vegetables. Import demand is being further stimulated by the explosion in supermarkets which require year-round availability of produce. Indeed, a recent trend throughout the developing world away from wet markets and toward supermarkets bodes well for international fresh produce trade, and hence, for California producers. It is estimated that the 30 largest retail grocery chains now account for at least 10 percent of world food sales. Many of these chains have stores located on several continents and their global procurement practices and cold chain management investments and exigencies mean that these modern produce departments must be kept full year-round. Since no country produces all of the fruits and vegetables it needs year-round, international trade will undoubtedly expand. As some California commodity sectors adjust to new market realities, structural adjustments may occur. However, in general, California agriculture remains very competitive with imports still a small share of supply. California growers and shippers substitute capital and technology for labor, enabling them to remain competitive even in the most labor-intensive horticultural crops. The primary crops for which sizable production has moved off-shore, in this case to neighboring Mexico, are those requiring bunching at harvest, such as green onions, asparagus and radishes. Still, over the next decade it is likely that many California commodity sectors will face greater import competition and more competition in export markets. While competition in third country markets will be strong, total international trade should expand as trade liberalization continues under the WTO.The principal marketing channels in the U.S. fresh fruit and vegetable marketing system are shown in Figure 1. Final value in 2002 is estimated to be at least $81 billion with roughly equal amounts distributed through food service and retail channels and around 2 percent comprised of direct farm to consumer sales.

In California, there are about 400 Certified Public Markets and many fresh produce growers participate in these markets for at least a part of their sales. Produce sold in retail or food service outlets may be procured directly from shippers or from wholesalers operating in terminal markets or in independent warehouses in local communities. Terminal markets have steadily declined in importance since the 1950s. Today there are major terminal markets serving only 15 cities, and these markets primarily handle the residual fresh market domestic production that cannot be marketed directly to retail or food service buyers. The largest terminal markets tend to be located near port areas since many imports are still handled by importers/intermediaries physically receiving the product upon arrival to the U.S. Terminal markets are no longer a factor in the distribution of processed food. The decline in terminal market share is largely a result of the increased buying power of integrated wholesale-retail buying entities, which operate large-volume centralized buying operations, and enhance efficiency by purchasing directly from the source, bypassing the wholesaler and thereby avoiding intermediary margins and handling costs. Also, the retailer- or food service-buyers are able to communicate directly with suppliers concerning important issues such as desired product quality, safety/traceability, packaging characteristics and shipment timing, improving their management of the supply chain. For fresh products, direct production-source-to buyer shipments have the additional advantage of not breaking the cold chain, better preserving product quality. Brokers may be used by either buyers or sellers at any level of the distribution system. Most brokers do not take title to or physically handle the goods, and, rather, assist in making the sale and possibly arrange transportation and other logistics. Their role had grown in importance since World War II. However, retail consolidation has been reducing the role of brokers as buyers seek closer relationships with preferred suppliers with strong category management skills. Today successful brokers tend to be those with global sourcing capabilities and account-specific service-orientations, including category management, designed to meet specialized buyer needs.Turning now to the opposite end of the marketing system, farm production of most commodities in California remains atomized in the sense that producer volumes, although often large in absolute terms, are small relative to the size of the market. It is estimated that there are about 16,500 fruit, vegetable and nut growers in California producing about half of the total volume of these crops grown in the U.S. However, most fresh produce growers don’t market their own produce, marketing instead via shippers acting as agents. Most shippers are large growers that have integrated their operations downstream into the marketing of their own production and the production of other growers—hence their designation as forward-integrated “grower-shippers.” These grower-shippers generally control harvesting, packing, and cooling, and arrange for domestic and export sales, transportation, and promotion of production. They are the dominant type of marketer of California fresh produce. According to the Red Book Credit Services there are around 5,000 fresh produce shippers in the U.S. as a whole, with about 900 located in California. These shippers are selling to an estimated total of 1,079 principal buyers, including 267 retail chains, 188 produce wholesalers, with the difference accounted for by independent retailers and other types of buyers. The bulk of retail chain purchases are being made by 161 retail chains each selling at least $64 million in 2001 . Consolidation at the buying end of the food marketing system has driven consolidation at the production level. Today’s large, integrated wholesale-retailer and food service buyers demand more services from their suppliers, tailored to their specific needs, including: category management, ripening and other special handling and packaging, including private labels, and year-round availability of a wide line of consistent-quality fruits and vegetables. Grower-shippers have responded with improved communication and information management programs and by becoming multi-regional and multi-commodity in focus.

Self-reported information on personal or family history of kidney disease was collected

All study procedures were approved by the University of California, Davis Institutional Review Board. AKI during the work shift, defined by a specified increase in serum creatinine from the preshift to the post shift measure, was the primary outcome of interest. Using the recommended definition and stages of injury from the Kidney Disease: Improving Global Outcomes group,AKI was defined as an increase of the post shift serum creatinine by ≥0.3 mg/dL or ≥1.5 times the preshift creatinine. AKI staging was based on the following: stage 1 ; stage 2 and stage 3 . Variables thought to be associated with AKI were selected a priori based on a review of the literature and feasibility of collecting data in the field. Demographic variables included sex , age and level of education . Clinical data were also obtained. Estimated glomerular filtration rate was calculated using preshift serum creatinine based on the Chronic Kidney Disease Epidemiology Collaboration equation and categorised as ≥90 mL/min/1.732, ≥60 to <90 mL/min/1.732 or <60 mL/min/1.732 . Body mass index was calculated from preshift height and weight measurements , and classified based on WHO recommendations as normal weight , overweight or obese . Diabetes status was defined by standard categories of HbA1c:no diabetes , prediabetes or diabetes . Seated blood pressure was categorised as recommended by the Joint Commission:normal blood pressure , prehypertension , or hypertension .Variables related to occupation included years in agricultural work , how the worker was paid or salary, and the farm task they engaged in most during that day.Descriptive statistics were calculated for the outcome and potential risk factors,hydroponic growing in pooled models and stratified by sex. Differences between males and females were tested using χ2 tests.

We determined AKI classification using the three stages of AKI. We then estimated the association of categories of per cent change in body mass and heat strain with AKI categories. In regression models, we dichotomised AKI as ‘any’ versus ‘none’. Logistic regression models assessed the associations between AKI and predictor variables. Because of concerns that sex might modify the effects of interest, we fit models stratified by sex in addition to pooled models. To aid in interpretation of the main effects in models which included interaction terms, we centred the PSI at a selected reference point and subtracted 4 from each value of PSI. We defined heat strain as a continuous variable based on the PSI. Our first model estimated the age-adjusted association of body mass change and heat strain on AKI. The second model added physiological or traditional risk factors, including weight class, diabetes status, hypertension status, and personal or family history of kidney disease. The final model added occupational risk factors, including years in farm work, payment method and farm task. We tested for effect modification of significant predictors . The Akaike and Bayes information criteria are model goodness of fit measures that incorporate a complexity penalty in favour of parsimonious models, with smaller values indicating better model fit. We report these measures for all models and used them to select the final model, with preference going to Akaike in case of conflicting results. Investigator beliefs about possible causal linkages were encoded using directed acyclic graphs, to develop a parsimonious set of candidate covariates . Covariates were also screened for variation. Those without sufficient variation were dropped . For some categorical variables, levels were combined to increase the precision of estimates involving these factors. For example, diabetes was collapsed to HbA1c<5.7 vs ≥5.7. Farm task was also collapsed to picking versus other. Participants with missing values for critical variables were dropped . A total of 300 participants were enrolled in the study. Five participants were missing either preshift or postshift creatinine measures, and an additional 12 were missing variables required for calculating heat strain, and the final analyses therefore included 283 participants . Our sample consisted of 182 males and 101 females, and the majority of the participans were from Mexico . The mean age was 38.6 years . Most participants were overweight or obese and were prehypertensive or hypertensive . Most had eGFR≥90 mL/min/ 1.732 , were not patients with diabetes or prediabetes , and had no personal or family history of kidney disease .

The mean maximum temperature was 38.0°C , and the mean maximum heart rate was 130 bpm . Statistically significant differences between the two sexes are shown in table 1. Overall, men reported higher levels of education than women. Men also had higher rates of prehypertension or hypertension than women . Men reported more years working in agriculture . There were also differences in the payment method, with 30.8% of men being paid by the piece versus 19.8% of women . Using changes in serum creatinine from preshift measures to post shift measures, 31 participants met KDIGO criteria for stage 1 AKI . An additional four participants met criteria for stage 2 AKI. Stratified by sex, 22 males and 13 females met criteria for AKI. Among men, 10 experienced heat strain, as estimated by PSI≥7.5, and 3 of those met criteria for AKI. No women experienced heat strain. Additionally, most of the sample experienced loss of body mass during the shift, but most did not lose more than recommended by OSHA. For example, 118 of men and 53 of women lost <1.5% body mass. However, five of the men and two of the women who lost ≥1.5% body mass met criteria for AKI. There were no statistically significant unadjusted associations of AKI with either heat strain or the change in body mass classification. Table 3 shows the results of logistic regression models. In the age-adjusted and sex-adjusted model, heat strain was associated with 1.29 adjusted odds of AKI . In this model, stratified by sex, the association among men was significant , but not among women. In the model adding physiological characteristics, the association of heat strain on AKI was virtually unchanged . Obesity was significantly associated with AKI . In the stratified model, men who were overweight or obese had reduced odds of AKI . There were no statistically significant associations among females. The addition of occupational characteristics in the final model did not appreciably change previous associations. However, piece rate work was associated with 4.24 adjusted odds of AKI . In stratified models, this association was not significant among men. Among females, the adjusted odds of AKI rose to 102.81 . Additionally, there was a statistically significant association of years in agricultural work to AKI among females . We modelled BMI as a continuous variable and found an inverse linear association with AKI: for every one-point increase in BMI, the odds of AKI went down 0.09 .

In subsequent pooled models, we added the interaction terms. None were statistically associated with AKI, nor did the additions appreciably change the estimations. Additionally, the model-fit statistics did not improve with the addition of the interaction terms . Incident AKI occurred in 35 participants in our sample of 283 California agricultural workers in the summer of 2014, in 22 of the 182 males and 13 of 101 females . In males, heat strain as estimated by PSI was associated with increased odds of incident AKI. In females, heat strain measurement was not associated with AKI, but occupational factors such as years in agricultural work and being paid by the piece were associated with AKI. While manifested differently between the two sexes, these findings together suggest that incident AKI is an occupational risk factor of agricultural work. The association of heat strain and AKI is not surprising, given that occupational heat strain has been associated with increased risk of renal insufficiency.In particular,hydroponic dutch buckets heat strain has been named as one of the potential risk factors for the development of a chronic kidney disease identified among agricultural workers in Central America, India and Sri Lanka.Moreover, heat exposure has been linked to AKI in other studies of otherwise healthy individuals such as athletes and military recruits.Given the high ambient temperatures in the Central Valley and the strenuous nature of agricultural work, our estimates of heat strain using the PSI were surprisingly lower than we expected, particularly among women, none of whom experienced heat strain. Other researchers have found agricultural work to be associated with high levels of heat strain both in the USA and in other countries.The Central Valley has low levels of humidity, which may allow workers to maintain cooler body temperatures than in other agricultural areas with high humidity. In addition, California is progressive in its prevention of heat related illness through regulations of the state Occupational Safety and Health Administration . Under Cal-OSHA requirements, farmers are required to provide heat illness prevention training for workers and offer regular breaks to cool off and rehydrate . Despite research that suggests workers do not remember the information provided in the trainings and do not take recommended breaks,443 our estimates of heat strain indicate that workers in our sample do not experience high levels of heat strain. This may be related to the different farm tasks performed, suggesting that not all farm work is strenuous. For example, the majority of the women were involved in packing or weeding, which is less strenuous than picking. However, the finding that heat strain in males was statistically associated with incident AKI suggests that agricultural workers who do experience high levels of heat strain are at risk of adverse renal effects.

Fortunately, current research into simple interventions, such as the use of backpack water reservoirs and the enforcement of rest periods during agricultural work, has had an effect on symptoms of heat strain and may provide a potential means of protecting the kidneys. The finding that women are affected differently by occupational exposures than men may be expected due to known gender differences in agricultural work. However, we were surprised to see that the occupational risk factors of years in agricultural work and payment method were associated with AKI in women in our sample. Studies of women’s experiences in agricultural work have documented the risk of sexual harassment or assault, which often occurs around bathroom facilities.Women may tend to limit drinking or eating during their work shift to reduce their need to use these facilities, or may delay trips to the bathroom during the work day out of fear for their safety. In a study of women in India who experienced heat stress at work, researchers found that delayed urination among women was associated with increased risk of urinary tract infection and AKI.The association of years of agricultural work and AKI among women in our sample could suggest that chronic delayed urination may increase the risk of AKI.Our finding that workers paid by the piece had higher odds of AKI requires further investigation, particularly because our sample size yielded imprecise estimates, and wide CIs may be attributed to the low numbers of women who experienced AKI and were paid by the piece . Piece rate work incentivises the worker to work harder and to take fewer breaks by financially rewarding higher productivity.Women who are paid by the piece may have an extra incentive to not visit the bathroom during the work shift, and piece rate work is associated with other poor health outcomes, including higher rates of accidents,musculoskeletal injury and risk-taking among workers.The independent association of piece rate work on AKI among women in our models suggests that piece rate work is a marker of conditions potentially damaging to kidney function, and that this mechanism is separate from heat strain or hydration status. Alternatively, piece rate work may be a better measure of the factors suspected to be involved in the development of AKI, which could explain the associations found here. In either case, modifications to the pay structure may help prevent AKI in agricultural workers. While not a risk factor for AKI in our estimations, the majority of workers in our sample experienced volume depletion after an agricultural work shift as measured by change in body mass. Other estimates of fluid intake among agricultural workers suggest that the amount of water workers drink is not sufficient to replace fluids and electrolytes lost during the work shift,as many do not believe they are at risk for injury and do not adequately rehydrate.