| Soils, Crops and Fertilizer Use |
|About this manual|
|Chapter 1: Down to earth - Some Important Soil Basics|
|What is soil, anyway?|
|Why do soils vary so much?|
|Topsoil vs. subsoil|
|The mineral side of soil: sand, silt, and clay|
|Distinguishing "tropical" soils from "temperate" soils|
|Organic matter - a soil's best friend|
|The role of soil microorganisms|
|Chapter 2: Trouble-shooting soil physical problems|
|Getting to know the soils in your area|
|Soil water-holding capacity|
|Chapter 3: Basic soil conservation practices|
|Chapter 4: Seedbed preparation|
|The what and why of tillage|
|Common tillage equipment|
|The abuses of tillage and how to avoid them|
|Making the right seedbed for the crop, soil, and climate|
|How deep should land be tilled?|
|How fine a seedbed?|
|Some handy seedbed skills for intensive vegetable production|
|Chapter 5: Watering vegetables: When? How Often? How Much?|
|It pays to use water wisely|
|Some common watering mistakes and their effects|
|Factors influencing plant water needs|
|Ok, so get to the point! how much water do plants need and how often?|
|Some methods for improving water use efficiency|
|Chapter 6: Soil fertility and plant nutrition simplified|
|Let's Make a Deal|
|How plants grow|
|Available vs. unavailable forms of mineral nutrients|
|Soil negative charge and nutrient holding ability|
|Soil pH and how it affects crops growth|
|Important facts on the plant nutrients|
|Chapter 7: Evaluating a soil's fertility|
|Plant tissue testing|
|Using visual "hunger signs"|
|Chapter 8: Using organic fertilizers and soil conditioners|
|What are organic fertilizers?|
|Organic vs. chemical fertilizers: which are best?|
|Some examples of successful farming using organic fertilizers|
|How to use organic fertilizers and soil conditioners|
|Chapter 9: Using chemical fertilizers|
|What are chemical fertilizers?|
|Are chemical fertilizers appropriate for limited-resource farmers?|
|An introduction to chemical fertilizers|
|Common chemical fertilizers and their characteristics|
|The effect of fertilizers on soil pH|
|Fertilizer salt index and "burn" potential|
|Basic application principles for N, P, and K|
|Fertilizer application methods explained and compared|
|Troubleshooting faulty fertilizer practices|
|Getting the most out of fertilizer use: crop management as an integrated system|
|Understanding fertilizer math|
|Chapter 10: Fertilizer guidelines for specific crops|
|Pulses (grain legumes)|
|Tropical fruit crops|
|Chapter 11: Liming soils|
|The purpose of liming|
|When is liming needed?|
|How to measure soil pH|
|How to calculate the actual amount of lime needed|
|How and when to lime|
|Chapter 12: Salinity and alkalinity problems|
|How salinity and alkalinity harm crop growth|
|Lab diagnosis of salinity and alkalinity|
|Appendix A: Useful measurements and conversions|
|Appendix B: How to determine soil moisture content|
|Appendix C: Spacing guide for contour ditches and other erosion barriers*|
|Appendix D: Composition of common chemical fertilizers|
|Appendix E: Hunger signs in common crops|
|Appendix F: Legumes for green manuring and cover-cropping in tropical and subtropical regions|
|Appendix G: Some sources of technical support|
|Appendix H: A bibliography of useful references|
Soil depth refers to the depth of the topsoil plus subsoil and can be easily determined with a shovel. Soils can be classified as being deep or shallow as follows:
Depth (Topsoil + Subsoil)
90 cm +
Less than 25 cm
Actual vs. Usable Depth: There's often a big difference between actual depth and usable depth, because the factors listed below can also limit root penetration:
• Excessive subsoil compaction.
• Hardpans and claypans ( explained in the drainage section).
• Poor drainage.
• Excessive subsoil acidity (very low pH).
• Potential rooting depth of the crop itself; some are naturally much deeper-rooted than others. (See Table 5-1 in Chapter 5 on water management.)
• Overly shallow watering can restrict depth of roots, since they will not grow into dry soil.
The Value of Deep Rooting
Deep rooting isn't necessarily essential for good crop yields. Some shallow soils can produce excellent yields if well managed. However, there are benefits to encouraging deep rooting:
• Better drought tolerance.
• Better nutrient uptake since the roots explore more soil.
• In irrigated crops, deeper rooting allows more water to be applied per application and more time between waterings. This can be very helpful in areas where farmers use furrow irrigation and receive water from the main ditch on an erratic schedule.
How to Encourage Deeper Rooting
• Use raised beds or ridges since they actually increase soil depth and provide a double layer of topsoil. However, they're not suited to dry conditions, because they dry out too fast.
• Double-digging will help encourage root growth into previously uninviting subsoil.
• Avoid overly shallow watering; this is most likely to occur on clayey soils because of their high water-holding capacity.
• Fertilizer use will stimulate deeper rooting.