Week 4 Fertiliser Effects

Question 1

Explain the components of the nitrogen cycle

Answer 1

Inputs
Dung, urine
Legumes fix from atmosphere
Scenecing plant material - majority 
Fertilser

Losses
Loss in animal products
N leaching = dec. pH

Question 2

Explain the role that nitrogen fixation has in Australian pastoral systems and outline any potential negative effects

Answer 2

Rhizobia (fast growing)
Bradyrhizobia (slow growing)

Nodulation is affected by fert placement, pH, temp, salinity

Proportion of total N in legume from bacteria 0.3 - 1.( high N in soil, fixation is low)

Need high Mo. Co, Ca for rhizobia to work

N fixation requires energy otherwise used for growth
5.1 mole CO2 burnt from every mole of NH4+
N fixing = 5x more cation uptake than ainiona= inc. acidity

Question 3

2 factors of Nitrogen Mineralisation

Answer 3

Temp and moisture

Question 4

Describe the optimum proportion of legume within a pasture and outline potential concerns when the legume component falls outside this range

Answer 4

20-50% legume will proved most of the N required in a system

Too Much legume = N leaching, acidity, Weed invasion

Too low = Dec. productivity, poor grass yeild, poor pasture quality

Question 5

Describe when nitrogen fertiliser may increase pasture production and explain what factors may affect efficiency.

Answer 5

Has biggest effect in winter as legumes aren’t fixing at this time
N fert is very inefficient
DON’T apply if soil temp is below 6 deg
10 kg DM increase is benchmark in Canberra

Question 6

Explain the components of the phosphorus cycle

Answer 6

Inputs
Dung - Soil OM
Phosphorus Fert (some turns to unavailable, little leached, some uptake)

OUT
Removal by animal products
1kg sold off farm
4kg 3-4 years used in pasture growth
1kg used that yr for pasture growth 
5kg fixed in soil for ever

200-400kg P/Ha

Question 7

Describe why phosphorus is such an important nutrient in Australian pastoral farming

Answer 7

Aust soils are inherently low in P (Except Basal soil -low S)

P essential to drive legume porduction- addative effect
More P = More N

Grasses are responsive to P too but only up to limit of N available
Inc. P = Inc. N = Acidity
Deep rooted perennials keep N from leaching

Question 8

Pros of P

Answer 8

Plants are able to cope a lot better with other stresses (water) with higher P
P required increase as grazing intensity increases

Wool is very responsive to P

Question 9

Outline the factors involved in determining the rate of phosphorus application

Answer 9

Soil Test
Removal - Product, loss due to landscape factors

Olsen P
No impact of soil P fixation capacity or texture on critical value (15mg P/kg Soil

Cowell P
Uses Phosphorus buffering index (PBI)

Question 10

Describe how you should prioritise phosphorus application on farm

Answer 10

Newest Pasture
Recently Eatablished Pasture
Low productivity pasture
No P areas

Question 11

Explain the importance of other nutrients in pastoral systems and how deficiencies can be corrected

Answer 11

Sulfur
Sulfate in soil
Soluble and readily leached
Not an issue when super is applied

K
Deficiency on high textured soils in high rainfall zone
SOils with history of removal - hay, silage
K leaches and accululates on sub soil of duplex soil

Mo
Required for N fixation of legumes
Over use = Cu defficiency
50-70g Mo/Ha every 5 years

Zn and Cu 2kg every 5 years