Library Open Repository

Manipulation of soil nitrogen to increase efficiency of mintuber seed production in Tasmania


Downloads per month over past year

Kirkham, J (2010) Manipulation of soil nitrogen to increase efficiency of mintuber seed production in Tasmania. PhD thesis, University of Tasmania.

[img] PDF (Front matter)
FRONT_June_2010...pdf | Download (260kB)
Available under University of Tasmania Standard License.

PDF (Whole thesis)
Final_Thesis_Ju...pdf | Download (3MB)
Available under University of Tasmania Standard License.


The management and manipulation of soil nitrogen (N) was investigated as a means
of influencing plant growth to increase tuber numbers produced from early generation
seed potato crops. The project focussed on crops grown from minitubers, small
potatoes produced under controlled environment conditions from tissue culture
plantlets. The use of minitubers as planting material for first field generation seed
potato crops reduces the risk of disease but is commercially challenging as the plants
tend to produce low tuber numbers, limiting the seed multiplication rate. The first
field generation is a high value crop grown on a small land area and there is therefore
potential for intensive management of factors such as nutrient supply to increase the
number of tubers and the subsequent rate of multiplication in the field.
Nitrogen has been shown to influence tuber number and tuber growth in both
hydroponics and field experiments, and was therefore the nutrient investigated in this
study. Initial glasshouse and laboratory experiments demonstrated that manipulation
of N availability could alter tuber development in potato plants. In contrast to
evidence in the literature from hydroponics experiments, a high constant N supply did
not delay or inhibit the onset of tuberization. High N supply increased tuber set and
growth, demonstrating the importance of sufficient N supply during early plant
growth up to tuberization. Rapidly reducing N supply to plants at the onset of
tuberization increased tuber growth rate by 60% compared to control plants two
weeks after treatment application. It was concluded that the treatment may reduce the
rate of tuber resorption during the tuber bulking phase, and therefore increase tuber
number at harvest.
Under field conditions, application of a leaching treatment based on calculations from
laboratory and glasshouse trials did not result in any significant change in tuber
number. Three potato cultivars were used in the trial and 150 plants per treatment
were assessed. Although N was applied to the crop as NO3
- to increase the likelihood
of leaching during treatment application, soil analysis indicated that NO3
concentrations were only reduced in the upper 20 cm of soil. Roots were distributed
throughout the top 40 cm of the soil and therefore plants still had access to significant
- concentrations after treatment application. The use of a drip irrigation system, the volume of water applied and the presence of anion adsorption contributed to
limited movement of NO3
- through the soil profile. The field results demonstrated a
need for better understanding of N movement in the Red Ferrosol soil so a more
effective strategy for rapidly reducing N concentrations in the root zone could be
Accurate and detailed measurements of water and NO3
- movement in the Red
Ferrosol soil were obtained from laboratory experiments. The presence of anion
adsorption was observed and therefore an adsorption isotherm for NO3
- was
developed. Using the data collected from the laboratory experiments, parameters for
the Hydrus 2D/3D soil model were validated for the soil and this model was used to
estimate the distribution of water and NO3
- under different irrigation scenarios in the
field. Simulations indicated an overhead irrigation system was a more effective
method for rapidly reducing soil NO3
- concentrations in the root zone than a dripper
system due to the predominantly vertical displacement of NO3
- however water
applications of over 300 mm of water were required. Further simulations in an
alternative sandy soil indicated that the leaching volume required was less than half
that of the Red Ferrosol due to the soils lower water holding capacity and absence of
anion adsorption. It was therefore concluded that serious consideration of soil type
should be made during the design of future experiments investigating strategic NO3
control in potato crops.
This study provides preliminary evidence that careful management of N in potato
crops has the potential to increase tuber growth rate and tuber number. However
treatments that involve manipulation of N availability are difficult to apply in field
environments where plant roots are widely distributed. Models such as Hydrus
2D/3D are useful tools for investigating water and nutrient movement under various
flow scenarios however reliability of model predictions depends on the level of
validation against measured data.

Item Type: Thesis (PhD)
Keywords: potato, hydrus, variable charge, nitrate absorption, ref ferrosol
Additional Information:

Copyright © the Author

Date Deposited: 22 Apr 2011 05:56
Last Modified: 11 Mar 2016 05:53
Item Statistics: View statistics for this item

Actions (login required)

Item Control Page Item Control Page