Soil Biology and Agricultural Practices

Flashcards about soil biology and agricultural practices, generated from lecture notes.

What percentage of the Earth's surface is suitable for agriculture?

Approximately 7.5%

What percentage of the world's agricultural land is no longer fertile and has been abandoned?

About 40%

We lose a soccer pitch of soil every five seconds due to what?

Erosion or desertification

If current soil management practices continue, how much topsoil do we have left?

About 60 years

How many tonnes of soil are lost from water erosion in Australia per hectare per year?

2.2 tonnes/ha/year

How much faster are we losing soil than it can be made?

100 times faster

Name examples of substances that are poisoning soil in China.

Cadmium, nickel, and arsenic

What contaminant from phosphate fertiliser causes problems on New Zealand dairy farms?

Cadmium

Two-thirds of all rivers in New Zealand are un-swimmable due to runoff of what?

Nitrogen

What happens when trees are removed from the landscape in relation to salt contamination?

Water table rises and carries salt with it

How does nitrogen fertilizer affect microbial activity?

Decreases microbial activity

Which potent greenhouse gas is always emitted when using nitrogen fertilizer?

Nitrous oxide

According to the lecture, the Green Revolution has resulted in what type of soil ecosystem?

A simpler, less stable soil ecosystem

What does a teaspoon of healthy agricultural soil contain?

Many billions of bacterial cells, kilometers of fungal hyphae, thousands of protozoa, hundreds of nematodes

Which type of microbe is often the most abundant in soils?

Bacteria

Besides plant nutrition, how do bacteria assist in soil health?

Decompose pesticides and other pollutants

What are the dominant bacterial groups found in the wheat rhizosphere?

Proteobacteria, Actinobacteria, Firmicutes

What is the major role of Actinobacteria in improving soil health?

Decompose organic materials, improve the availability of nutrients, inhibit the growth of plant pathogens

Which type of soil fungi degrades lignin?

Saprophytic fungi

What are the three major groups of protozoa found in soil?

Flagellates, Amoebae, Ciliates

What are the two main groups of soil microarthropods?

Mites (Acari) and Springtails (Collembola)

What are the key roles of soil microarthropods?

Mineralise nutrients, regulate populations of the soil fauna

What do Enchytraeids (potworms) ingest?

Ingest organic matter and associated microorganisms

How do tunnels dug by ants benefit the soil?

Increase air and water flow in soil

What are the three ecological groups of earthworms?

Epigeic, Anecic, Endogeic

What are the attributes of earthworm casts?

Nutrient-rich and the nutrients are in a form readily available to plants

How do bacteria in the genus Rhizobium enter root tissue?

Modify host cells so that nodules are formed

How much nitrogen is usually produced by Rhizobium, depending on legume species and growing conditions?

100-200 kg N/ha/year

How do soil organisms like nematodes mineralise nutrients?

Release nutrients from microbial cells

Nutrient cycling occurs because predators have a _ compared to their prey.

Higher C/N ratio than their prey

What are arbuscles?

Branched hyphae within root cells with an absorptive function

Why do the hyphae of AM fungi improve P uptake?

They can enter small pore spaces and explore a greater soil volume

How do mycorrhizal fungi act in dry environments?

Acts as an extension of the root system, improving drought tolerance

What do Arbuscular mycorrhizal fungi produce to improve soil structure?

Binding agent (glomalin)

Glomalin provides what two purposes?

Sealant and rigidity

What is glomalin?

Glycoprotein

Name agricultural practices that disrupt AMF and reduce glomalin production

Frequent inputs of P fertiliser, Long fallow periods, Frequent tillage, Soil fumigation

What is contained in a disease-suppressive soil?

Active and diverse biological community

Name mechanisms by which organisms in disease-suppressive soil regulate populations of pests

Predation, parasitism, competition, production of antibiotics