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Florence-Graham, United States

Stone K.C.,Water and Plant Research Center | Sadler E.J.,U.S. Department of Agriculture
Transactions of the ASABE

Spatial irrigation of agricultural crops using site-specific variable-rate irrigation (VRI) systems is beginning to have widespread acceptance. However, optimizing the management of these VRI systems to conserve natural resources and increase profitability requires an understanding of the spatial crop responses. In this research, we utilize a recently developed spatially explicit analysis model to reanalyze spatial corn yield data. The specific objectives of this research were to (1) calculate a suite of estimates (estimated yield, rainfed yield, maximum yield, and irrigation at maximum yield) and provide credible intervals (measures of uncertainty) around these estimates for comparing with the previous analysis, and (2) examine whether the conclusions from this rigorous re-analysis were different from the prior analysis and if the results would force any modifications to the conclusions obtained with the prior analyses. The spatially explicit analysis was achieved using a mixed model formulation of bivariate penalized smoothing splines and was implemented in a Bayesian framework. This model simultaneously accounted for spatial correlation as well as relationships within the treatments and had the ability to contribute information to nearby neighbors. The model-based yield estimates were in excellent agreement with the observed spatial corn yields and were able to estimate the high and low yields more accurately than the previous analysis. Credible intervals were calculated around the estimates, and the majority encompassed the observed yields. After calculating estimates of yield, we then calculated estimates of other response variables, such as rainfed yield, maximum yield, and irrigation at maximum yield. These estimated response variables were then compared with previous results from a classical statistical analysis. Our conclusions supported the original analysis in identifying significant spatial differences in crop responses across and within soil map units. These spatial differences were great enough to be considered in irrigation system design and management. The major improvement in the 2014 re-analysis is that the model explicitly considered spatial dependence in calculating the estimated yields and other variables and thus should provide improved estimates of the impact of spatial differences for use in irrigation system design and management. © 2016 American Society of Agricultural and Biological Engineers. Source

Lamm F.R.,Kansas State University | Stone K.C.,Water and Plant Research Center | Dukes M.D.,University of Florida | Howell T.A.,U.S. Department of Agriculture | And 2 more authors.
Transactions of the ASABE

This article is an introduction to the "Emerging Technologies in Sustainable Irrigation: A Tribute to the Career of Terry Howell, Sr." Special Collection in this issue of Transactions of the ASABE and the next issue of Applied Engineering in Agriculture, consisting of 16 articles selected from 62 papers and presentations at the joint irrigation symposium of ASABE and the Irrigation Association (IA), which was held in November 2015 in Long Beach, California. The joint cooperation on irrigation symposia between ASABE and IA can be traced back to 1970, and this time period roughly coincides with the career of Dr. Howell. The cooperative symposia have offered an important venue for discussion of emerging technologies that can lead to sustainable irrigation. This most recent symposium is another point on the continuum. The articles in this Special Collection address three major topic areas: evapotranspiration measurement and determination, irrigation systems and their associated technologies, and irrigation scheduling and water management. While these 16 articles are not inclusive of all the important advances in irrigation since 1970, they illustrate that continued progress occurs by combining a recognition of the current status with the postulation of new ideas to advance our understanding of irrigation engineering and science. The global food and water challenges will require continued progress from our portion of the scientific community. This article serves to introduce and provide a brief summary of the Special Collection. © 2016 American Society of Agricultural and Biological Engineers. Source

Zeng L.,Crop Genetics Research Unit | Campbell B.T.,Water and Plant Research Center | Bechere E.,Crop Genetics Research Unit | Dever J.K.,Texas A&M University | And 7 more authors.

Determination of environmental influence on seed traits is critical for genetic improvement of seed quality in upland cotton (Gossypium hirsutum L.). The objective of this study was to analyze the relative contribution of environment and genotype (G) for seed oil, nitrogen (N), and gossypol contents using historical data from the regional high quality (RHQ) tests conducted from 1996 through 2013. The 18-year tests of RHQ were divided into six 3-year cycles with an average of about 20 genotypes and 7–10 testing locations (loc) in each cycle. Variance components of oil, N, and gossypol contents were estimated in each cycle and expressed as percentages of the total variance. Highly significant G × loc effects were identified for all seed quality traits in each cycle. For oil content, variance estimates of G to the total variance ranged from 20 to 57 % in different cycles. For N content, loc was the main source of variance with variance estimates of loc to the total variance ranging from 44 to 73 % in different cycles. In most cycles, loc and G were the main source of variance for free-gossypol content. For most seed quality traits, there was not a clear trend of changes among testing cycles for the variance estimates of G to the total variance. Broad-sense heritability for oil content, N content, and free-gossypol ranged from 0.79 to 0.96, 0.65 to 0.86, and 0.28 to 0.93, respectively. Highly significant G × loc interactions indicate that multiple location trials for testing seed quality traits are necessary. However, heritability estimates for these seed traits indicate stability across environments as well as the potential for genetic improvement. Significant reduction in seed index was observed in half of the testing cycles with a range of 10.4–9.52 within cycles. Correlation between seed index and oil content was positive with r values ranging from 0.23 to 0.77 in different cycles. © 2015 Springer Science+Business Media Dordrecht (outside the USA) Source

Karunanithi R.,University of South Australia | Szogi A.A.,Water and Plant Research Center | Bolan N.,University of South Australia | Naidu R.,University of South Australia | And 6 more authors.
Advances in Agronomy

Phosphorus (P) is a macronutrient essential for all living organisms. Regrettably, it is a finite resource since phosphate rock (PR) is the main material used for production of P fertilizers. Globally, the demand for quality PR is escalating due to many factors including increasing human population. Inevitably, the demand for PR will exceed its supply capacity. This condition will be very difficult to manage as living systems have no alternative for P. Moreover, P use efficiency is low; only 15-20% of applied P is used by crops and animals. Globally, the remaining P is shunted into various waste streams. These waste streams include large quantities of effluents rich in P from both municipal and industrial wastewater treatment systems and manure from livestock production. The P present in these waste streams poses a threat to the environment by nutrient enrichment resulting in serious ecological issues such as eutrophication of waterways. However, P in these waste streams, if economically recovered, can contribute to a sustainable management of P resources. This review covers the following aspects: global importance of P as an essential nutrient; efficient and sustainable utilization of P; waste stream production, their suitability for P recovery, and limitations; current and emerging technologies for recovery of P; and the use of recovered P material. Finally, future research needs are identified associated with P recovery from waste streams and reuse in agriculture. © 2015 Elsevier Inc. Source

Stone K.C.,Water and Plant Research Center | Bauer P.J.,Water and Plant Research Center | Andrae J.,Clemson University | Busscher W.J.,Water and Plant Research Center | And 3 more authors.
Transactions of the ASABE

In the southeastern region of the U.S., the cattle industry has a critical need for sustainable hay production. Yet this production is threatened by frequent short-term regional drought. This drought threat can be mitigated by properly managed irrigation. In this study on Tifton 85 bermudagrass, irrigation management, nitrogen fertility levels, and harvest interval were evaluated for their impact on hay quality and yield. The experimental treatments were arrayed in a split-plot design with harvest interval as the main treatment; irrigation by nitrogen (N) levels were the subplots. Treatments had four replicates and were repeated for two years. The optimal irrigation rate was set to maintain soil water potentials below -30 kPa. When needed, the full irrigation treatment received a 12.5 mm irrigation application. The reduced irrigation treatments received water at rates of 0%, 33%, and 66% of the full irrigation rate. In addition, each irrigation treatment had nitrogen rates of 168, 336, and 504 kg N ha-1. The irrigation and nitrogen treatments were harvested at four-week or eight-week intervals. Total harvests per year ranged from three to six. Over both years and for all harvests, there was no irrigation-nitrogen interaction for hay yield. Over all harvests, nitrogen significantly increased bermudagrass hay yield, nutrient concentrations, and forage quality. Forage quality was higher for the four-week harvest interval. Throughout the study, forage quality was maintained within desired industry standards. When irrigation was required, it significantly increased hay yield. During these periods, the four-week and eight-week 100% irrigation treatments yielded 612 and 1600 kg ha-1 greater, respectively, than the non-irrigated treatments. The four-week harvest interval was more sensitive to irrigation. Additionally, we observed a linear relationship between non-irrigated bermudagrass hay yields and average soil water potential. As soil water was depleted, non-irrigated hay yields decreased 31 kg ha-1 per kPa. Timely supplemental irrigation to maintain soil water potentials above -30 kPa can increase bermudagrass yields. Thus, irrigation management should be critically assessed for its potential role in sustaining hay production in the southeastern Coastal Plain. © 2012 American Society of Agricultural and Biological Engineers. Source

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