Introduction

Essential nutrients and micro-nutrients

Cation exchange capacity

Potassium

Sodium, magnesium, calcium

Introduction to soil fertility

	Fertility is the capacity of the soil to provide the nutrients needed for plant growth
	No quantitative definition or measurement
	Includes chemical composition (CEC), parent material (basic igneous rocks), physical structure (porous, high water holding capacity, aerated), soil biological activity (soil organic matter)
	Fertility is the basis of plant production
	Soil fertility determines the performance and quality of desirable forage species

Macro- & micro-nutrients, essential & non-essential

	macro-nutrients are those essential minerals that exceed 0.1% of plant dry weight
	C, H, O, N, P, K, S, Ca, Mg
	micro-nutrients (or trace elements) are those essential minerals that are typically <0.05% of dry weight (500 ppm)
	include silicon (Si), boron (B), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), chlorine (Cl), molybdenum (Mo) and nickel (Ni) (in order of decreasing abundance)
	non-essential nutrients are those nutrients present in plants but are not essential for plant function. Typically many of these are required for animal function
	include silicon (Si), chlorine (Cl), sodium (Na), iodine (I), chromium (Cr), cobalt (Co), and selenium (Se)

Cation exchange capacity

Potassium (potash) (pg 281-283)

	Historically was applied to soil in the ash from blast furnaces
	Released into the soil by the mineral apatite
	or applied as fertilizer
	essential in plants, promotes nodulation in legumes, important in osmotic adjustment (drought tolerance and freezing resistance), metabolic processes
	in fertilizer is measured as K2O Molecular Weight K 39.098 78.2 83% O 15.9994 16.0 94.2
	in soil - is measured as kgK/ha (lb/acre) or ppm (g/1000 kg)
	It takes 4 lbs/acre of K2O to increase soil test by 1 lb/acre It takes 8 lbs/acre of K2O to increase soil test by 1 ppm
	Soil K should be at least 300 kg/ha (270 lb/ac), depending on CEC, and soil K supplying power
	in forage is measured as ppm (g/1000 kg) or % (g/100g) desirable levels in forage are at least 2.5%
	high losses when forage is removed as hay/silage that must be replaced by fertilizer (see pg 277)

Back to top

Continue

Sodium, calcium, magnesium

	Na - not required by plants, and in excess can displace K+ - when present in plants it does help regulate osmotic balance - it is required by animals, hence is required in forage
	Mg - required by plants for enzymatic function (chlorophyll) - typical levels are 0.25-0.30% - it is required by animals, deficiency results in hypomagnesemia of lactating cows - can be applied as dolomite (Ca CO3/MgCO3) - can be suppressed by Ca (in lime) or high rates of K
	Ca - minor role in plants, contributes to good soil structure - typical levels are 1-2% - it is required by animals for bone growth - can be applied as lime (Ca CO3) or dolomite (Ca CO3/MgCO3) - increases soil pH

Copyright © The Ohio State University All rights reserved.