How do you aim to address issues related to livestock and crop systems, as well as forage quality and management practices?

Both animal and crop sciences are very important in different agricultural areas, and I am fortunate in being able to work in a field that combines the two so well. Forage production, although considered an agronomic practice, is mostly intended to support animal production systems and animal nutrition. It can be tricky to produce the right forage to achieve high biomass and yield, since it is well known that high forage mass can negatively impact overall forage quality. Animal performance is a sound theoretical definition of forage quality and can be useful for relative comparison among forages grazed. Ruminants tend to be very selective, grazing forage that is higher in digestibility and protein, with a lower percentage of fibre than the remaining stubble. Since the quality of a forage tends to decline as it accumulates mass and matures, it is very important to determine when to harvest or graze in order to balance forage production and animal production.

With whom are you working to further your research in this area, both industrially and academically?

I’ve been on the faculty at the University of Tennessee, Knoxville (UT) Department of Plant Sciences since 2013, collaborating with many of my departmental colleagues as well as with faculty from other departments within the UT Institute of Agriculture, such as Animal Science, Agricultural and Resources Economics, and Biosystems Engineering and Soil Science. Externally, I have been working with The Ohio State University, Auburn University, North

Carolina State University and others. I have also continued to collaborate with universities in Brazil, such as the University of São Paulo-ESALQ and São Paulo State University, as well as organisations like Embrapa. On the industry side, I have been collaborating with various seed companies in testing different grass and legume cultivars.

In what ways are you supporting producers in their efforts to better manage forage harvesting and grazing?

Most of the research I have been conducting aims to facilitate the daily operations and management of livestock producers. At UT, since I do not hold an extension appointment, I can dedicate all my time to research. I work closely with the UT Forage Extension Specialist Dr Gary Bates, and we constantly discuss ways to address concerns and difficulties that producers currently have. In my view, finding solutions through the development of new research projects and then disseminating our knowledge is the best strategy for supporting livestock producers.

Where do you expect the next big advances in your field to be? Do you have any exciting plans to conduct further research in the pipeline?

One big advance that I can certainly foresee within the US is the integration of animal and crop production into one system. This type of system is not new by any means, and several researchers in Brazil have already been successfully conducting research in this area. However, the concept is fairly new both in the US and many other countries. We are living in a world in which space has become

limited, and instead of invading untouched areas, I foresee the possibility of integrating different agricultural production systems such as livestock, forage and crops, forestry, water quality, soil quality and nutrient cycling.

Having moved from Brazil to the US, what benefits have you enjoyed in your academic and professional career?

Since the beginning of my career, I have considered international networks to be the most powerful and important way of disseminating research and knowledge. We live in a world that is constantly changing and improving, especially now in this new era of social media. Globalisation is all around us, and the world has become smaller with regard to our growing avenues of communication and ease of access to new research and partnerships.

With that being my main overall goal, I have taken advantage of the benefits of living outside my home country of Brazil, which include the opportunity to share recently acquired knowledge, findings and techniques more widely. Partnerships at an institutional level are also important; UT is constantly developing new collaborations that will give US students the opportunity to broaden their experiences overseas, and vice versa.

Brazilian agronomist and crop researcher Dr Renata Nave discusses her unique efforts to inform US agricultural practice with principles garnered from the cattle ranchers of South America

Ruminations on grazing

60 INTERNATIONAL INNOVATION

AgRONOmy

A group of expert agronomists based at the University of Tennessee, Knoxville, USA, has recently shared a valuable evidence base to farmers on how best to optimise the performance of their cattle by improving the quality of the forage available to them

The grass is always greener

THE AMOUNT OF beef produced in Brazil is nothing short of phenomenal. In 2014, almost 17 per cent (around 10 million metric tonnes) of the world’s beef came from Brazil. The South American giant is second only to the US – and not by much. The country’s status as a rising economy and its small size compared with the current champion make this an impressive enough feat – but there is another challenge that elevates it to an extraordinary level. The tropical flora available to feed cows in Brazil is actually quite poor nutritionally, and certainly less nourishing than that available to cattle in more temperate zones.

The problem is that tropical grasses tend to have higher concentrations of lignin, a tough, fibrous biological polymer that is the main constituent of wood. Lignin is very useful to plants because it helps them to maintain a solid structure, as well as providing some level of protection from insects that might feed on or otherwise damage them, and ensuring that water can be distributed efficiently throughout the plant. These advantages are doubly important in the tropics, where extreme weather conditions and large numbers of insects exert a greater pressure on the local flora. As a result, tropical plants grow quickly but, since they are harder to digest, they tend to make worse forage for cattle.

GLOBAL KNOWLEDGEHow then have Brazilian farmers managed to do so well from this seemingly poor starting point? The answer lies in their management techniques; in order to make the most from

tropical grasses, they need to graze their cattle at the right time, and in the right way. Years of experience have helped Brazilian cattle farmers to hone their techniques, but optimal forage management is important in temperate climates as well as tropical ones, and the methods practiced in Brazil – as well as the principles that underlie their success – may have value for cattle farmers around the world.

Now, researchers at the University of Tennessee, Knoxville (UT) are making the most of this key knowledge, first acquired more than 4,000 miles away. Dr Renata Nave, a native of Brazil, has a research appointment at UT’s Department of Plant Sciences – and she has made it her goal to apply her unique experience and advanced training to answer some of the most critical questions posed by livestock and crop producers as well as agricultural professionals. “My main interest is in disseminating some of the knowledge I have acquired while in Brazil in order to produce cattle in a cost-effective and economical way here in the US,” she explains.

A PERFECT BALANCEWhen it comes to optimising forage for animal production, the key is in balancing production against nutritional content. When plants – like the tropical grasses of Brazil – put out new growth, that material will usually be tender and easily digestible, as well as containing more nutrients than a well-established part of the plant. This poses a problem in terms of forage production, in which grasses may either be grazed by livestock or harvested for

www.internationalinnovation.com 61

FORAGE PRODUCTION MANAGEMENT ISSUES AND INCREASING SUSTAINABILITY

OBJECTIVESTo develop science-based solutions to address livestock and crop systems, focusing on forage production management problems by increasing sustainability through improved forage quality and management practices.

PARTNERSUSA:Institute of Agriculture, University of Tennessee, Knoxville:Department of Animal ScienceDepartment of Agricultural and Resources EconomicsDepartment of Biosystems Engineering and Soil Science

The Ohio State UniversityAuburn UniversityNorth Carolina State University

Brazil:University of São Paulo-ESALQSão Paulo State UniversityEmbrapa

CONTACTDr Renata NaveAssistant Professor

Department of Plant SciencesUniversity of Tennessee2431 Joe Johnson DriveKnoxville, Tennessee 37996-4561USA

T +1 931 486 2129 E rnave@utk.edu

http://bit.ly/1GiBVWP

RENATA NAVE is a researcher native of Brazil, where she has completed both her Bachelor’s and Master’s degrees, and studied forages and grasslands with a focus

on evaluating different grazing strategies to improve forage productivity and forage nutritive value. In 2008, she was awarded a scholarship to complete her PhD degree at The Ohio State University, where she continued her studies in crop science and forage crops.

use later; if grass is allowed to grow long, then more forage will be available – but the quality will be lower. In Brazil, cattle are typically raised in big herds on large pastures; they can therefore browse freely and selectively, preferring nutritious new-growth grass and making the most of the tropical forage.

The work Nave’s team has conducted towards optimal forage began with an important study on management strategies for xaraés palisade grass, a tropical grass that is prolific in South America. The researchers wanted to find out which grazing strategies would make the best use of the plant, and they compared approaches based on time – grazing the land every 28 days – and the ability of the grass canopy to intercept sunlight. The results demonstrated that the highest nutritional content was achieved by grazing in a targeted fashion, when the light interception of the grass reached 95 per cent.

SERVED ON A PLATEWhile discussing relative light interception is informative for agronomic researchers, it is not a particularly useful measurement for agricultural workers in the field. In industry, the standard tool for measuring grass cover is the rising plate meter, a device that measures the height of the grass canopy above the ground and approximates the mass of dry matter per unit area from a small number of sample readings. Using this tool, farmers can get a good idea of the value of the pasture available to them – and can also define a ‘slope’ of mass values across all of their pastures, as grazing livestock are rotated between them.

It seems like a simple process, but an element of complexity is introduced in the calibration equations that convert the height reading from the meter into the dry mass estimate that the user is primarily interested in. Far from being universal, this equation will vary depending on the time of year, species of grass and sward composition – but most practitioners stick with the basic equation because they do not have sufficient information to improve its accuracy. In order to help producers achieve this, Nave and her colleagues published a 2012 paper on optimal calibration for rising plate meters, concluding that frequent alterations were most important in spring, when slope coefficients decrease most rapidly.

OUTSTANDING IN THE FIELDParticularly influential in the last few years, however, have been the in-field studies carried out by Nave and her collaborators towards better understanding and

recognising nutritive value in grasses. Published in 2013, the first of these papers looked at how nutritive value could be recognised by grass canopy characteristics – in other words, how farmers could gauge the value of a particular paddock merely by looking at it. The results were surprising: simply from the dry mass of the grass, the researchers were able to accurately model the digestibility of the neutral detergent fibre component.

The second study, which concluded in 2014, built on this work by examining the actual vertical distribution of nutrients in the living plant over the seasons. Nave and her group found that the nutritional content of a sward changed dramatically as it aged, with the neutral detergent fibre increasing in line with dead material that accumulated in the grass canopy through time. The paper placed particular emphasis on the importance of maintaining the grass in a vegetative state – especially in spring, when the accumulation of mass accelerates.

WATCH THIS SPACEToday, Nave and her group continue their important work, seeking to keep pace with the needs of farmers and growers. In recent years, nitrogen prices have risen dramatically in the south-eastern US, pushing many producers to look for alternatives; accordingly, the UT researchers are now beginning to explore fertilisation methods and their impact on forage production. “We are soon to publish this data to the public and, though more research is needed in this area, we are confident that we could find solutions to improve forage production in a more economical system,” Nave reveals.

In Brazil, cattle are typically raised in big herds on large pastures; they can therefore browse freely and selectively, preferring nutritious new-growth grass and making the most of the tropical forage

62 INTERNATIONAL INNOVATION