# A statistical handbook for agricultural field trials specialists

## Which is the best Field Trial Manual for agriculture?

Manual no. 1, MR 1 Field trial manual Principles, planning and Implementation of Agricultural Field Trials By Peter Kurt Hansen with staff of the Shifting Cultivation Research Sub-programme Shifting Cultivation Research Sub-programme Lao Swedish Forestry Programme Luang Prabang, Lao P.D.R August 1997 Field trial manual 20040103 i Preface

## What is the field trial manual 20040103?

Field trial manual 20040103 i Preface This manual introduces the principles and methods of field trial experiments. It was originally intended for staff of the Lao Swedish Forestry Programme and for staff in its associated target districts. Most of these officials have little theoretical and practical experience in carrying out field trials.

## Who is the author of the Handbook on statistics?

The Handbook was prepared by Peter Lys, Senior Consultant, and Franck Cachia, Associate Statistician at FAO’s Statistics Division (ESS) from 2011 to 2014, under the guidance of Sangita Dubey and Carola Fabi, Senior Statistician and Statistician, respectively, in ESS.

## What is the scope and statistical unit of commercial farming?

The scope is commercial farms registered in the taxation system; the statistical unit is the farming unit, which consists of one or more farms involved in cropping and/or livestock activities. Link to the on-line questionnaire: www.statssa.gov.za/agriculture

## What is statistical analysis?

Statistical analysis involves a sequence of mathematical computations for comparing treatments and evaluating whether any observed differences are truly a result of the change in practices, or if the differences may be due to chance and natural variation. This section looks at statistical analysis in more detail, …

## What are the two types of errors in statistical analysis?

There are two kinds of errors in statistical analysis: a Type I error and a Type II error. A Type I error occurs when you identify a difference when in fact the treatments were not different. A Type II error is the opposite, when you determine there is no difference yet in fact there really is. A probability level, typically 5 percent in field …

## What does it mean when the difference between treatment practices is greater than the LSD value?

Any difference between treatment practices that is greater than the LSD value means the difference you identified is most probably a result of the treatment, whereas a smaller difference is likely to be the result of chance—you cannot guarantee the same results if you repeated the experiment.

## What does it mean to be statistically significant?

Rather, a statistically significant finding means that the researcher is confident that the result is reliable within certain parameters. In other words, the treatment had an actual effect on the system, and the results were not the product of chance.

## What is a small standard deviation?

A small standard deviation means that the data is clustered closely around the mean; a large standard deviation means the data is spread out over a wider range of values. The standard deviation is expressed in the same units as the data (e.g., bushels per acre).

## What is field trial research?

It is a systematic way of comparing plantproduction technologies on a small piece of land. The different methods that we compare arecalled treatments. In a field trial we try to keep all factors equal that can influence the quantity orquality of plant production, except the different treatments. Examples of treatments are differentvarieties of a crop species, different planting dates of a crop, different levels of fertilizers appliedto a crop, and different crop rotations.

## What is the objective of field trials?

The objective of field trials is to compare various treatments. The different treatment will givedifferent yields and other results. However, other factors also influence the trials and the yieldsobtained from the plots. These factors include:

## What are the causes of error in field trials?

In upland field, especially recently cleared shilling cultivation fields, both type ofsoil fertility distribution are common. Ash deposits, termite mounds, decomposing roots, treestumps, cow dung and intercropping are all likely to increase the patchy fertility distribution.

## Why are field trials important?

Field trials carried at research stations may be useful in testing new technology under relativelycontrolled conditions. However, such trials often says little about the suitability for the newtechnology under the environmental and socio-economic conditions that face farmers.

## What is field trials in Laos?

Most agricultural and forestry field trials in Laos areadaptive research trials. This meansthat trials aim at testing already known technology, and at modifying the technology to the localconditions. This kind of research is therefore sometimes called technology verification trials.Adaptive agricultural research would normally be expected to produce useful results within andrelatively short time, usually 2-4 years. Some research aims at generating new technology, suchas new crop varieties or new cropping systems, and is therefore called technology generatingtrials.

## Where are technology generating trials carried out?

Such trials may be carried out both at research stations and in farmers’ fields. Thestatistical procedures and trial designs are usually similar whether carried out as on-station or on-farm trials.

## What is an experimental plot?

An experimental plot is the area where one treatment of one replication is assigned. The normalsize of a plot is 5-40 square meters. Very small plots give a lot of uncertainty because:

## 1. Choose a uniform site

Avoid fields that have areas of poor drainage or sandy spots. Also, make sure that the field received consistent management in the recent past. Some things that could cause problems include:

## 2. Use replication and randomization

Simply splitting a field, or comparing one field to another, cannot provide reliable answers to agronomic questions. Even with no differences in management, you will find a higher yield in one field vs. another, and similarly with one half of a field vs. the other.

## 3. Account for application equipment

While you can measure yield to whatever the width of your combine head is, you need to keep in mind that a fertilizer spreader or sprayer will have a different width and therefore dictate how big your treatment strips or areas are.

## 4. Control variables

If you are going to answer a question, you need to ensure that the treatment variable being tested is the only variable that changes. Changing crop hybrid/variety, spot treatment of weeds or insects, or variable nitrogen rates can bias the study’s results.

## 5. Oversee quality control

Nearly everyone with experience conducting on-farm trials has a story of something that happened on a site that ruined the trial. Even though you think you are on the same page as your input providers, or others conducting field operations, it is often best to be there in person (and preferably riding along) when treatments are being applied.