An economic evaluation of site-specific input application Rx maps: evaluation framework and case study

Precision Agriculture - Commercial consultants frequently sell site-specific crop input management recommendation maps (Rxs) to their farmer-clients. This study proposes a method to empirically...     

Minimizing environmental impacts of grassland weed management: can Cirsium arvense be controlled without herbicides?

Invasion by undesirable plants, such as Cirsium arvense, can constrain attempts to conserve and restore biodiversity in extensively managed temperate grasslands, but control with herbicides can cause environmental harm. We contrasted herbicides with more environmentally sustainable weed control strategies. Six‐year, large‐scale randomized block experiments were established to determine optimum combinations of grazing management and mechanical or herbicide treatments to control thistles within lowland and upland grazing systems. Factorial combinations of tight vs. lenient grazing in spring and autumn with additional treatments of winter grazing were compared. Thistle control methods were applied in sub‐treatments for the first 2 years: cutting twice yearly, herbicide wiping, and cutting followed by herbicide application. Thistle abundance decreased under lenient grazing in spring, autumn and winter at the lowland site, under lenient spring and winter grazing in the uplands and under cattle compared with sheep grazing. Herbicide wiping was the most effective control measure and cutting the least, but effects of all weed control sub‐treatments were lost rapidly, so lenient grazing was sufficient to give long‐term thistle control. Lenient grazing and herbicide wiping also caused small declines in non‐target forb diversity. Control of creeping thistle can therefore be achieved without herbicides because lenient grazing in spring and autumn can decrease thistle populations to sufficiently low levels. Severe infestations can be more rapidly controlled using herbicides, but are better avoided at botanically diverse sites. Ecologically‐based weed control strategies have great potential, but require well designed field experiments, which run for sufficiently long periods to allow community‐level impacts to develop.     

From Agronomic Research to Farm Management Guidelines: A Primer on the Economics of Information and Precision Technology

An ultimate purpose of much agronomic and agricultural economic research is to provide management guidelines (e.g., on application rates of fertilizer, seed, and herbicides) to farmers. Ideally, farm management guidelines or recommendations would be determined by applying sound economic theory to data from agronomic experiments. While information provided by agronomic data about the relationship between crop yields, managed inputs, soil characteristics, and weather variables has always been valuable, we argue in this paper that because such information and precision agriculture technology are economic complements, the advent of precision agriculture technology has made information provided by agronomic experiments now even more valuable than ever. The purpose of this paper is to point out and respond to two practical implications of the complementarity between precision technology and information from agronomic research. The first implication is that because precision technology has made information more valuable, it is also more costly now when agronomists make mistakes in using economic theory to derive incorrect farm management recommendations from the information. Therefore it is more important than ever that agronomists understand some basic economic theory about agricultural production and precision technology. Our response is to provide here an economic primer on precision agriculture and information. We also recommend increased collaboration between agronomists and agricultural economists in precision technology research. The second implication is that, because precision technology has made the information more valuable, there is more need than ever for long-term, multi-regional agronomic experiments. For before scholarly experts can provide separate management recommendations for many very small areas of farmers' fields, they will need to know much more than they currently do about the relationships between crop yields, input application rates, soil characteristics, and weather variables. Our response is to call for agronomists to begin designing and implementing such experiments, and to call for increased public funding of such experiments.     

The value of conducting on-farm field trials using precision agriculture technology: a theory and simulations

Precision Agriculture - The objectives of this article are to examine the practicality of on-farm precision experiments to sufficiently lower the costs of acquiring the information...     

Estimating the epidemiology of emerging Xylella fastidiosa outbreaks in olives

Xylella fastidiosa is an important insect-vectored bacterial plant pathogen with a wide host range, causing significant economic impact in the agricultural and horticultural industries. Once restricted to the Americas, severe European outbreaks have been discovered recently in Italy, Spain, France, and Portugal. The Italian outbreak, detected in Puglia in 2013, has spread over 100 km, killing millions of olive trees, and is still expanding. To date, quantified assessment of important epidemiological parameters useful for risk assessment and management, such as transmission rates, symptomless periods, and time to death in field populations, has been lacking. This is due to the emergent and novel nature of the outbreak and length of time needed to monitor the course of disease progression. To address this, we developed a Bayesian method to infer epidemiological parameters by fitting and comparing compartmental epidemiological models to short snapshots of disease progression observed in multiple field plots. We estimated that each infected tree with symptoms is able to infect around 19 trees per year (95% credible range 14–26). The symptomless stage was estimated to have low to negligible infectivity and to last an average of approximately 1.2 years (95% credible range 1.0–1.3 years). Tree desiccation was estimated to occur approximately 4.3 years (95% credible range 4.0–4.6 years) after symptom appearance. However, we were unable to estimate the infectiousness of desiccated trees from the data. Our method could be used to make early estimates of epidemiological parameters in other emerging disease outbreaks where symptom expression is slow.     

Modelling historical landscape changes

Landscape Ecology - Historical maps of land use/land cover (LULC) enable detection of landscape changes, and help to assess drivers and potential future trajectories. However, historical maps are...     

Evaluation of the Minolta SPAD‐502 chlorophyll meter for nitrogen management in corn

The field study investigated the relationship of Minolta SPAD 502 (SPAD) readings to applied nitrogen (N) fertilizer rate, corn (Zea mays L.) yield, and leaf N concentration. The experiment was conducted on a total of six sites in Illinois during 1991 and 1992. Ten different open pedigree corn hybrids were grown at a final population of 65,000 plants ha^‐1. Nitrogen was applied at four rates(0, 90, 180, and 270 kgN ha^‐1) as 28% liquid N solution. Significant main effects of environment (E), and hybrid (H), and E x H interaction were detected for all measured parameters. SPAD readings and leaf N concentration at all sampling times (V7, R1, and R4) as well as grain N concentration were affected by N fertilizer rate. Maximum mean grain yield and maximum grain N concentration were obtained at 110 and 195 kg N ha^‐1, respectively. At all sampling times the correlation of SPAD readings to N fertilizer rate were low but significant (R=0.22 at V7 and R1, R=0.11 at R4). SPAD correlation to corresponding leaf N concentration improved over time. The Pearson correlation was R=0.33 at V7 and increased to R=0.78 at R4. The SPAD meter did a good job at providing a measure of the relative greenness of living leaves at a specific point in time. Chlorophyll readings can therefore be useful in detecting N deficiencies in growing crops. But, the SPAD meter cannot be used to make accurate predictions of how much fertilizer N will be needed by a crop during the future growing season. We conclude then that the SPAD meter will be most useful as a diagnostic aid rather than a tool for N management in corn.     

A reduced organic carbon component in martian basalts

The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.