title: The effects of varying intensity cultivation on soil quality in a maize cropping system

authors: McKay, Emily Grace

abstract: Maize is the primary crop grown on arable land in the Waikato region, predominantly established on Allophanic soils due to their well-drained and resilient properties. Full cultivation (FC) is universally adopted in cropping systems and associated with increased soil aeration and successful seed establishment, however, has been shown to reduce soil quality through declines in soil organic matter (SOM) and soil structure. SOM (TC & TN) decline and aggregate stability are considered important indicators of soil quality in cropping systems as they pose the greatest risk to long term productivity and profitability. Soil degradation can be reduced through conservation tillage such as no-till (NT) and strip-till (ST). Previous studies have investigated the effect of cultivation intensity on soil quality and consistently found that NT systems have greater carbon (C) levels and aggregate stability at the soil surface than higher intensity cultivation systems. 

The main aim of this thesis was to determine whether there were significant differences in soil quality between varying intensity cultivation systems (FC, ST, NT) on Allophanic soils in the Hamilton Basin. Further aims were to determine whether differences in the inherent soil properties of the Horotiu silt loam and Bruntwood silt loam would influence the soil quality within the study area, and to identify whether soil quality was influenced by an interaction between cultivation intensity and soil type. 

Twelve plots with four replicates of each cultivation treatment were sampled and soil quality measured using seven soil quality indicators (total C (TC), total nitrogen (TN), mineralisable nitrogen (N), soil pH, Olsen P, bulk density (BD), and macroporosity (MP)) and three additional cropping indicators (aggregate stability, penetration resistance, and visual soil assessment). Mechanically driven cores for TC and TN analysis were taken from 0 – 7.5 cm, 7.5 – 15 cm, and 15 – 30 cm. Significant differences in TC, TN, and aggregate stability in the top 10 cm were detected between cultivation treatments (p < 0.05). NT was shown to be the most beneficial cultivation for a maize cropping system, indicated by significantly greater TC (3.98 %), TN (0.41 %), and aggregate stability (0.97 mm, MWD) at the soil surface than higher intensity cultivation systems (For FC; TC = 3.56 %, TN = 0.37 %, aggregate stability = 0.62 mm). Additionally, significant differences in TC and TN were found between soil types, where Horotiu silt loam had significantly greater TC and TN (e.g. for 0 – 10 cm; Horotiu: TC = 4.02 %, TN = 0.42 %; Bruntwood TC = 3.52 %, TN = 0.36 %). There were also significant differences in aggregate stability, MP, and BD between soil types, where the Horotiu silt loam had higher aggregate stability (0.82 mm, MWD), MP (14 %) and lower BD   (0.96 t m-3) and Olsen P (82.9 μg g-1) than the Bruntwood silt loam (Aggregate stability = 0.73 mm, MP = 12 %, BD = 1.05 t m-3, Olsen P = 105.5 g g-1). Where there were interactions between cultivation intensity and soil type, significant differences were detected in aggregate stability and penetration resistance, where the Horotiu silt loam under NT had higher aggregate stability (1.07 mm, MWD) and penetration resistance (2.00 MPa) than all other combinations. Conversely, the Bruntwood silt loam under FC had the lowest aggregate stability (0.55 mm, MWD) and penetration resistance (1.63 MPa). 

Many of the soil quality values in the study area fell below or exceeded target ranges set for cropping systems, regardless of cultivation treatment or soil type. This is due to the intensive nature of cropping systems, use of heavy machinery, removal during harvest, and poorly defined target ranges. This study highlights how differences in inherent soil properties between two soil types within the same soil order can greatly influence soil quality. Previous data showed cultivation intensity did not significantly influence maize yield at this stage in the trial.  This research therefore suggests NT systems result in higher SOM content and greater aggregate stability and therefore may be a more suitable cultivation system for continuous maize cropping without decreasing productivity or profitability.

text: The effects of varying intensity cultivation on soil quality in a maize cropping system Maize is the primary crop grown on arable land in the Waikato region, predominantly established on Allophanic soils due to their well-drained and resilient properties. Full cultivation (FC) is universally adopted in cropping systems and associated with increased soil aeration and successful seed establishment, however, has been shown to reduce soil quality through declines in soil organic matter (SOM) and soil structure. SOM (TC & TN) decline and aggregate stability are considered important indicators of soil quality in cropping systems as they pose the greatest risk to long term productivity and profitability. Soil degradation can be reduced through conservation tillage such as no-till (NT) and strip-till (ST). Previous studies have investigated the effect of cultivation intensity on soil quality and consistently found that NT systems have greater carbon (C) levels and aggregate stability at the soil surface than higher intensity cultivation systems. 

The main aim of this thesis was to determine whether there were significant differences in soil quality between varying intensity cultivation systems (FC, ST, NT) on Allophanic soils in the Hamilton Basin. Further aims were to determine whether differences in the inherent soil properties of the Horotiu silt loam and Bruntwood silt loam would influence the soil quality within the study area, and to identify whether soil quality was influenced by an interaction between cultivation intensity and soil type. 

Twelve plots with four replicates of each cultivation treatment were sampled and soil quality measured using seven soil quality indicators (total C (TC), total nitrogen (TN), mineralisable nitrogen (N), soil pH, Olsen P, bulk density (BD), and macroporosity (MP)) and three additional cropping indicators (aggregate stability, penetration resistance, and visual soil assessment). Mechanically driven cores for TC and TN analysis were taken from 0 – 7.5 cm, 7.5 – 15 cm, and 15 – 30 cm. Significant differences in TC, TN, and aggregate stability in the top 10 cm were detected between cultivation treatments (p < 0.05). NT was shown to be the most beneficial cultivation for a maize cropping system, indicated by significantly greater TC (3.98 %), TN (0.41 %), and aggregate stability (0.97 mm, MWD) at the soil surface than higher intensity cultivation systems (For FC; TC = 3.56 %, TN = 0.37 %, aggregate stability = 0.62 mm). Additionally, significant differences in TC and TN were found between soil types, where Horotiu silt loam had significantly greater TC and TN (e.g. for 0 – 10 cm; Horotiu: TC = 4.02 %, TN = 0.42 %; Bruntwood TC = 3.52 %, TN = 0.36 %). There were also significant differences in aggregate stability, MP, and BD between soil types, where the Horotiu silt loam had higher aggregate stability (0.82 mm, MWD), MP (14 %) and lower BD   (0.96 t m-3) and Olsen P (82.9 μg g-1) than the Bruntwood silt loam (Aggregate stability = 0.73 mm, MP = 12 %, BD = 1.05 t m-3, Olsen P = 105.5 g g-1). Where there were interactions between cultivation intensity and soil type, significant differences were detected in aggregate stability and penetration resistance, where the Horotiu silt loam under NT had higher aggregate stability (1.07 mm, MWD) and penetration resistance (2.00 MPa) than all other combinations. Conversely, the Bruntwood silt loam under FC had the lowest aggregate stability (0.55 mm, MWD) and penetration resistance (1.63 MPa). 

Many of the soil quality values in the study area fell below or exceeded target ranges set for cropping systems, regardless of cultivation treatment or soil type. This is due to the intensive nature of cropping systems, use of heavy machinery, removal during harvest, and poorly defined target ranges. This study highlights how differences in inherent soil properties between two soil types within the same soil order can greatly influence soil quality. Previous data showed cultivation intensity did not significantly influence maize yield at this stage in the trial.  This research therefore suggests NT systems result in higher SOM content and greater aggregate stability and therefore may be a more suitable cultivation system for continuous maize cropping without decreasing productivity or profitability.

year: 2020

title: Variance anisotropy in kinetic plasmas

authors: Parashar, Tulasi N.

subjects: Science & Technology

abstract: Solar wind fluctuations admit well-documented anisotropies of the variance matrix, or polarization, related to the mean magnetic field direction. Typically, one finds a ratio of perpendicular variance to parallel variance of the order of 9:1 for the magnetic field. Here we study the question of whether a kinetic plasma spontaneously generates and sustains parallel variances when initiated with only perpendicular variance. We find that parallel variance grows and saturates at about 5% of the perpendicular variance in a few nonlinear times irrespective of the Reynolds number. For sufficiently large systems (Reynolds numbers) the variance approaches values consistent with the solar wind observations.

text: Variance anisotropy in kinetic plasmas Solar wind fluctuations admit well-documented anisotropies of the variance matrix, or polarization, related to the mean magnetic field direction. Typically, one finds a ratio of perpendicular variance to parallel variance of the order of 9:1 for the magnetic field. Here we study the question of whether a kinetic plasma spontaneously generates and sustains parallel variances when initiated with only perpendicular variance. We find that parallel variance grows and saturates at about 5% of the perpendicular variance in a few nonlinear times irrespective of the Reynolds number. For sufficiently large systems (Reynolds numbers) the variance approaches values consistent with the solar wind observations.

year: 2016-06-10

title: Ka awatea

authors: Levy, Michelle Patricia

abstract: This book realises a long held vision to boldly claim our space in psychology: showing how we as Māori practitioners, researchers, and teachers of psychology realise our belief in the potential of psychology to contribute positively to the lives of our whānau. Celebrating our diversity, while at the same time being drawn together by our commonalities, these pages offer a space where all our contributions can be honoured. Our title, originating from Virginia’s chapter, which in turn originated from a well-known whakataukī, expresses the distinctiveness and beauty of manu Māori who herald the dawn, share stories and who listen to the voices of the universe. Like the manu, our reo expresses our whakaaro and our shared beginnings that unite and connect us across the dimensions of wairua, land, sea and air.

text: Ka awatea This book realises a long held vision to boldly claim our space in psychology: showing how we as Māori practitioners, researchers, and teachers of psychology realise our belief in the potential of psychology to contribute positively to the lives of our whānau. Celebrating our diversity, while at the same time being drawn together by our commonalities, these pages offer a space where all our contributions can be honoured. Our title, originating from Virginia’s chapter, which in turn originated from a well-known whakataukī, expresses the distinctiveness and beauty of manu Māori who herald the dawn, share stories and who listen to the voices of the universe. Like the manu, our reo expresses our whakaaro and our shared beginnings that unite and connect us across the dimensions of wairua, land, sea and air.

year: 2016