Soil And Plant Nutrition

Question 1

The concentration of nitrates in the soil is governed by…..

Answer 1

The microbial mineralization of organic matter and the conversion of ammonium to nitrate.

Question 2

How much nitrogen is lost in ammonia volatilisation when broadcasting urea? (Average)

Answer 2

5-27%

12% average

Question 3

Ammonia volatilisation can be influenced by;

Answer 3

Soil properties, weather, crop cover, stubble.

Question 4

At what relative humidity does urea dissolve?

Answer 4

> 72% RH

Question 5

Rule of thumb for urea braoadcast application?

Answer 5

> 15mm of rain within 2 days of spreading.

Question 6

What is the form of nitrogen that is plant available?

Answer 6

Nitrate and ammonium.

Question 7

How does ammonium volatilisation occur?

Answer 7

Ammonium is converted into ammonia (gas). Higher soil pH and temp, the more likely ammonium is to be converted into volatilising ammonia gas.

Question 8

Best practice urea application.

6

Answer 8

1. Incorporation into cultivated soil.
2. Do not broadcast on a wet soil.
3. Avoid broadcasting before a windy day.
4. Volatilisation is greater when it is warm.
5. Clay soils greatly reduce risk of ammonia volatilisation.
6. Banding is not ideal.

Question 9

Herbicide fallow, loses ?? tons of carbon over 11 years

Answer 9

42 tons/ha