Cover Image
close this book Soils, Crops and Fertilizer Use
View the document About this manual
View the document Acknowledgements
close this folder Chapter 1: Down to earth - Some Important Soil Basics
View the document What is soil, anyway?
View the document Why do soils vary so much?
View the document Topsoil vs. subsoil
View the document The mineral side of soil: sand, silt, and clay
View the document Distinguishing "tropical" soils from "temperate" soils
View the document Organic matter - a soil's best friend
View the document The role of soil microorganisms
close this folder Chapter 2: Trouble-shooting soil physical problems
View the document Getting to know the soils in your area
View the document Soil color
View the document Soil texture
View the document Soil tilth
View the document Soil water-holding capacity
View the document Soil drainage
View the document Soil depth
View the document Soil slope
close this folder Chapter 3: Basic soil conservation practices
View the document Rainfall erosion
View the document Wind erosion
close this folder Chapter 4: Seedbed preparation
View the document The what and why of tillage
View the document Common tillage equipment
View the document The abuses of tillage and how to avoid them
View the document Making the right seedbed for the crop, soil, and climate
View the document How deep should land be tilled?
View the document How fine a seedbed?
View the document Some handy seedbed skills for intensive vegetable production
close this folder Chapter 5: Watering vegetables: When? How Often? How Much?
View the document It pays to use water wisely
View the document Some common watering mistakes and their effects
View the document Factors influencing plant water needs
View the document Ok, so get to the point! how much water do plants need and how often?
View the document Some methods for improving water use efficiency
close this folder Chapter 6: Soil fertility and plant nutrition simplified
View the document Let's Make a Deal
View the document How plants grow
View the document Available vs. unavailable forms of mineral nutrients
View the document Soil negative charge and nutrient holding ability
View the document Soil pH and how it affects crops growth
View the document Important facts on the plant nutrients
close this folder Chapter 7: Evaluating a soil's fertility
View the document Soil testing
View the document Plant tissue testing
View the document Fertilizer trials
View the document Using visual "hunger signs"
close this folder Chapter 8: Using organic fertilizers and soil conditioners
View the document What are organic fertilizers?
View the document Organic vs. chemical fertilizers: which are best?
View the document Some examples of successful farming using organic fertilizers
View the document How to use organic fertilizers and soil conditioners
close this folder Chapter 9: Using chemical fertilizers
View the document What are chemical fertilizers?
View the document Are chemical fertilizers appropriate for limited-resource farmers?
View the document An introduction to chemical fertilizers
View the document Common chemical fertilizers and their characteristics
View the document The effect of fertilizers on soil pH
View the document Fertilizer salt index and "burn" potential
View the document Basic application principles for N, P, and K
View the document Fertilizer application methods explained and compared
View the document Troubleshooting faulty fertilizer practices
View the document Getting the most out of fertilizer use: crop management as an integrated system
View the document Understanding fertilizer math
close this folder Chapter 10: Fertilizer guidelines for specific crops
View the document Cereals
View the document Pulses (grain legumes)
View the document Root crops
View the document Vegetables
View the document Tropical fruit crops
View the document Tropical pastures
close this folder Chapter 11: Liming soils
View the document The purpose of liming
View the document When is liming needed?
View the document How to measure soil pH
View the document How to calculate the actual amount of lime needed
View the document How and when to lime
View the document Don't overlime!
close this folder Chapter 12: Salinity and alkalinity problems
View the document How salinity and alkalinity harm crop growth
View the document Lab diagnosis of salinity and alkalinity
close this folder Appendixes
View the document Appendix A: Useful measurements and conversions
View the document Appendix B: How to determine soil moisture content
View the document Appendix C: Spacing guide for contour ditches and other erosion barriers*
View the document Appendix D: Composition of common chemical fertilizers
View the document Appendix E: Hunger signs in common crops
View the document Appendix F: Legumes for green manuring and cover-cropping in tropical and subtropical regions
View the document Appendix G: Some sources of technical support
View the document Appendix H: A bibliography of useful references

Fertilizer trials

Well-run fertilizer trials can be very helpful. There are 3 kinds:

• Test strips

• Field experiments (farm experiments)

• Field tests (field trials, result tests)

Test Strips

Running test strips through a field is a quick and easy way to test crop response to different fertilizer rates and nutrient combinations. Test strips have less statistical significance than formal trials, but they do allow farmers to conduct some research on their own farms, which can be very useful. A researcher's test of statistical significance is usually a 95 or 99 percent likelihood that the results were due to the treatment applied rather than to chance. Farmers (and most of us) would probably settle for a much less stringent figure and try a new practice, even if there were only a 75 percent chance of getting a response.

To reduce the influence of soil variations, each treatment tested should consist of several strips 2-3 rows wide placed in different parts of the field. The soil should still be uniform visually and in terms of past management. Don't rely on just one season's results, since weather and pests can influence yields.

Fertilizer rates for test strips: Consult your extension office and Chapter 9 of this manual.

Field Experiments (Farm Experiments)

These are designed to be statistically valid and require much more effort and care to set up and manage. They are designed to determine the most profitable kind and amount of fertilizer needed for a given crop and soil. Suppose you want to try 3 different rates of fertilizer. It's not simply enough to mark out one test plot and 3 fertilized plots. Each of these 4 "treatments" needs to be replicated 3-4 times and laid out within a bloc in a randomized manner. Each of the 12-16 plots are only a few rows wide and several meters long. Plot size, plant population, and fertilizer rates have to be carefully measured, along with yield differences. It's a good idea to repeat a trial for 2-3 years to take into account weather variations.

Formal experiments require much time, skill, attention to detail, and scientific discipline. They are not something that you should do on your own. However, you can play a very useful role in a well conducted and ongoing fertilizer testing and demonstration program.

Field Tests (Field Trials, Result Tests)

This type of research tests the best fertilizer type and rate determined from the farm experiments above, but this time under actual farming conditions. There are normally just 2 plots: the "control" plot (traditional practice) and the "treatment" plot (improved practices). Rather than rely on randomization and replication of the plots on each farm, the field test gets its statistical validity from being conducted on a number of farms with fairly similar conditions. In most cases, fertilizer will be only one of several improved practices making up the treatment plot. The plots should be large enough so that realistic farming methods can be used. To be valid, the farmer and other usual labor should carry out the practices themselves with some initial instruction and supervision by the extension worker.

Experiments/Trials vs. Demonstrations

The experiments and trials above seek to develop fertilizer recommendations for local conditions that will be the most affordable and profitable for the farmers involved. Don't succumb to the natural and prevalent temptation to use such tests as demonstrations. After all, a demo is designed to provide farmers with "living proof" of the benefits of a new practice (or package of practices) - one that has first proven its worth under local conditions. This syndrome of promoting without adequate prior testing has cost many an extension worker an irreparable loss of credibility. Testing is always the first stage; promoting comes later.

NOTE: For more information on experiments, trials, and demos, refer to the Peace Corps/ICE manual, Traditional Field Crops (M-13).