R. J. Paton

The impacts of nitrogen fertilisation and increased stocking rate on pasture yield, soil physical condition and nutrient losses in drainage from a cattle‐grazed pasture

Abstract The effects of increasing nitrogen (N) fertiliser inputs, and associated cattle stocking rates, on pasture yield and composition, soil physical quality and nutrient losses in drainage were measured in an experiment on permanent white clover/ryegrass pastures in eastern Southland, New Zealand. Treatments were established on hydrologically‐isolated replicate plots (900 m2) where pastures received annual fertiliser N inputs of 0, 100, 200 or 400 kg ha–1 and were grazed throughout spring, summer, and autumn of each year by non‐lactating dairy cattle. Our aim was to determine if N fertilisation of cattle pastures led to the deterioration of pasture or soil quality, or to the excessive loss of nutrients in drainage over the 3–4 years after such land management started. Pasture and soil monitoring showed that N fertilisation and increased stocking rate resulted in large, but variable, increases in pasture yield, with little discernible effect on soil physical condition, as evidenced by twice‐yearly measurements of soil bulk density, percentage of soil pores >300 μm, soil macroporosity (volumetric percentage of pores >30 μm), hydraulic conductivity, and air permeability. A cyclical pattern of spring soil compaction followed by recovery over summer, autumn, and winter was evident in the 0–5 cm soil layer within all treatments. Mean annual pasture responses to applied fertiliser N were 14.8, 12.9, and 9.1 kg DM kg–1 N applied in the 100, 200, and 400 N treatments, respectively, with greater responses observed in spring than in autumn in 3 out of 4 years. N fertilisation significantly increased losses of nitrate‐N and Ca in drainage but had no significant effect on K, Mg, Na, sulphate‐S, Cl, and P drainage losses. Within the context of the potential for enriching groundwater supplies of domestic drinking water, these losses suggest that annual fertiliser N inputs should not exceed approx. 170 kg N ha–1 yr–1 at this site. Considered from the perspective of potential surface water enrichment with P and N promoting nuisance weed and algal growth, losses of N and P in drainage water exceeded currently accepted guidelines, especially for N. The responses measured in this study represent a system that has recently undergone an improvement in soil fertility along with a change from sheep to cattle grazing. We thus caution that our findings pertain to short‐term changes in soil and plant responses and may not accurately reflect those in a system that has been in long‐term (>20 years) equilibrium.

Effects of cattle treading and natural amelioration on soil physical properties and pasture under dairy farming in Southland, New Zealand

Abstract The effects of current dairy cow grazing practice, reduced levels of grazing, and stock exclusion on soil physical properties and pasture dry matter production were investigated under dairy farming in Southland. Current grazing practice involves rotational grazing with dairy cows from September to May each year, with no grazing during winter. For the reduced grazing treatments, cattle were excluded during the 3rd, or combined 3rd, 4th, and 5th grazing cycles, or for half‐day grazing intervals to reduce grazing intensity. Macroporosity increased by 70% in the ungrazed treatment compared with current grazing practice (control) within four months of dairy cow exclusion. Air permeability was increased by over two orders of magnitude 18 months after trial commencement, and saturated hydraulic conductivity increased by 200% to the 10‐cm soil depth. Macroporosity, air permeability, and hydraulic conductivity for the reduced grazing treatments were intermediate between the control and ungrazed treatments. Relationships between macroporosity and pasture relative yield are presented. At 97% relative pasture yield, the level of macroporosity was 11.5–11.7% (v/v) in three silt loams.

A survey of soil physical properties on sheep and dairy farms in southern New Zealand

Abstract The study compared soil macroporosity, bulk density, air permeability, and hydraulic conductivity on 97 sheep and 87 dairy farm sites surveyed in Southland and South Otago, New Zealand. Soil physical properties of 4 soil groups (15 soils) were investigated. Soils on sheep farms surveyed had significantly greater air permeability than soils on dairy farms, averaged over 0–15 cm. Soils on sheep farms had significantly greater saturated hydraulic conductivity (86 mm h‐1 and 26 mm h‐1) than soils on dairy farms (32 mm h‐1and 10 mm h‐1), at 0–5 cm and 10–15 cm, respectively. Macroporosity decreased from 0–5 cm to 5–10 cm, at a significantly greater rate on dairy farms (by 3.6% v/v) than sheep farms (by 1.5% v/v). Bulk density increased between 0–5 cm and 5–10 cm by a greater amount for dairy farms (0.16 Mg m‐3) than for sheep farms (0.12 Mg m‐3). Macroporosity on some Fragic Pallic Soils was considered limiting for plant growth, while Firm Brown Soils were regarded as well structured and most likely to resist treading damage.

Soil physical quality under cattle grazing of a winter-fed brassica crop

Abstract This 2-year study investigated the effects of winter brassica forage crop grazing treatments on soil physical properties on a Fragic Pallic soil, susceptible to compaction, in South Otago, New Zealand. Soil physical measurements including bulk density, percentage of pores >300 μm, macroporosity (air-filled porosity; percentage of pores >30 μm), total porosity, air permeability, and saturated hydraulic conductivity (Ksat) were taken 1.5 and 4 months after completion of winter grazing in year 1, and 2.5 months after grazing in year 2. Treatment main effects in year 1 for macroporosity were ungrazed crop (P < 0.05, 15.5%), established pasture (12.2%), crop on-off grazing (12.8%), crop grazed with back fence (9.6%), and current practice (strip grazing without a back-fence, 8.6%). During both winters the soil was generally more compact at 0.05–0.10 m depth than at 0.15–0.20 m, particularly for the current practice treatment, which may increase the risk of overland flow. Micro-topography differences between hump and hoof-hollow areas for the current practice treatment were also investigated during one sampling, with very low values of Ksat at 0–0.05 m in hoof-hollow areas (P < 0.05, 5 mm/h), compared with hump areas (129 mm/h). Overall, the crop on-off grazing treatment and, with some exceptions, the grazed with back fence treatment have some merit for reducing damage to soil physical properties compared with current practice.

Nitrogen and phosphorus losses in mole and tile drainage from a cattle-grazed pasture in eastern Southland

Abstract An experimental system for monitoring drainage outflows from mole‐ and tile‐drained plots is described, and nitrogen (N) and phosphorus (P) losses in drainage are reported for Year 1 of a 4‐year study examining nutrient losses in drainage from a pasture in Southland. Twelve plots (0.09 ha), grazed by non‐lactating dairy stock, were artificially drained by installing a mole and tile drainage network. A metering station was used to monitor drainage flow rate from six of these plots using a V‐notch weir and a shaft encoder system. Drainage water samples were collected on a flow proportional basis using either an automated water sampler triggered by the flow monitoring system, or by manual collection during daylight hours. The amount of nitrate‐N lost in drainage water in this first year of study was 25 kg N ha–1, resulting in a volume‐averaged nitrate‐N concentration of 6.9 mg N litre–1. Although this is a significant loss of potentially plant available N, the average nitrate‐N concentration of the drainage water was below the 11.3 mg N litre–1 standard adopted by the New Zealand Ministry of Health for acceptable nitrate levels in drinking water. Mean dissolved reactive P and total P concentrations in drainage waters were 23 and 74 μg P litre–1, respectively. Analysis of forms of P showed 61 % of the total P lost in the drainage was in the form of particulate P, which may reflect the recent introduction of mole and tile drainage to this site.

Soil compaction and recovery cycle on a Southland dairy farm: implications for soil monitoring

This paper quantifies soil compaction and natural recovery of soil physical properties during a 3-year trial on a dairy farm in Southland, New Zealand. The study investigated the magnitude of soil compaction over spring, and natural recovery of soil physical properties over summer and autumn. Changes in soil physical condition were measured while pastures were intermittently grazed by lactating dairy cows, and also over winter when cows were removed from pasture. Soil bulk density at 0–5 cm increased (P 30 μm) at 0–5 cm decreased (P < 0.001) from 13.5 to 7.5%, with similar trends in spring 2002. Many of the soil physical properties showed significant recovery over summer and autumn. Bulk density decreased (P < 0.001) by 0.09 Mg/m3, from December 2001 to May 2002. Soil macroporosity also recovered markedly during summer and autumn. Macroporosity increased (P < 0.001) from 12.5% in December 2001 to 18% in May 2002. Significant changes in soil compaction and recovery were also measured at 5–10 cm depth. For many soil physical properties, recovery over winter was much less than over summer and autumn. Implications of the compaction and recovery cycle are discussed in terms of measurement protocols appropriate to routine monitoring of soil physical condition.

Cattle treading and phosphorus and sediment loss in overland flow from grazed cropland

This 1-year study investigated the effect of dairy cow treading on soil physical properties and sediment and phosphorus (P) loss via overland flow from pasture and cultivated soil used for wintering dairy cows in southern New Zealand. Treading decreased soil macroporosity and Ksat, and increased overland flow volumes. Treading increased mean suspended sediment concentration in overland flow in the cultivated + trodden treatment (2.6 g/L) compared with ungrazed pasture (0.44 g/L) and ungrazed cultivated (0.98 g/L) treatments over 2 slope positions. Following grazing in the cultivated + trodden treatment, only 25% more sediment was lost in subsequent overland flow events (2.09 and 2.63 g before and after grazing, respectively), and mean total P (TP) losses increased by >250% (from 0.7 to 2.5 mg P). Meanwhile in the cultivated but ungrazed treatment, sediment and TP loss decreased. The increased loss of sediment and P following grazing in the cultivated + trodden treatment was attributed to P from cattle dung, and soil disturbance. Consequently, wintering of animals on cultivated paddocks with forage crops increases the risk of losing much P, especially in particulate form.

EFFECT OF SHEEP STOCKING INTENSITY ON SOIL PHYSICAL PROPERTIES AND DRY MATTER PRODUCTION ON A PALLID SOIL IN SOUTHLAND

Abstract This 3‐year study examined the extent of damage to soil physical properties of a Pukemutu silt loam (Pallic Soil) and the loss of ryegrass‐white clover pasture production caused by intensive winter grazing at 1800 sheep ha−1. Macroporosity, pore size distribution, bulk density, and hydraulic conductivity were measured at 5‐cm incremental soil depths to 15 cm to assess changes in soil compaction. Soil smearing on intensively winter‐grazed plots suggested that soil structural damage had occurred. Soil physical tests, three weeks after winter grazing, in August 1994 and 1995, however, showed only slight compaction at the surface. Macroporosity in the 0–5 cm soil depth was significantly reduced from 16.4% to 12.1% by the intensive winter grazing treatment. Soil pores were water‐filled leading to plastic deformation rather than compaction. Spring pasture production was also significantly decreased (21%) following the 1994 winter grazing, but growth recovered the following summer. Macroporosity was gen...

Restricting the grazing time of cattle to decrease phosphorus, sediment and E. coli losses in overland flow from cropland

This study investigated the effects of grazing management of brassica crops during winter on soil physical properties and sediment, phosphorus (P), and E. coli loss via overland flow. Dairy cows were allowed either unrestricted grazing, grazing restricted to 3 h, or no grazing. Treading in the unrestricted treatment decreased soil bulk density and saturated hydraulic conductivity (Ksat), and increased surface roughness, loads and concentrations of suspended sediment, and E. coli and P loss in overland flow relative to the ungrazed treatment. Only bulk density was different in the restricted compared with the ungrazed treatment. For total P, the mean load in overland flow from the unrestricted grazing treatment after grazing was 3.31 mg/plot compared with restricted grazing (0.74 mg/plot) and ungrazed (0.76 mg/plot) treatments, with most of the increase in particulate form. E. coli concentrations only exceeded water quality guidelines in the first event after grazing, and only in the unrestricted grazing treatment. We found that restricting grazing on forage crops during winter was beneficial for minimising contaminant loss.

Land-use intensification in New Zealand: effects on soil properties and pasture production

Land-use intensification requires more farm inputs to sustain or increase farm product outputs. However, a common concern for land-use intensification is the potential deterioration of soil. The North Otago Rolling Downlands (NORD) region of New Zealand is drought prone, and although traditionally limited to extensive sheep farming, there are large-scale conversions to intensive cattle grazing operations such as dairy farming resulting from an irrigation scheme commissioned in 2006. Pallic soils (Aeric Fragiaqualf in US Soil Taxonomy) such as those in the NORD region are prone to soil compaction because of their ‘high’ structural vulnerability under intensive management. To address these concerns, a field trial was established on a common NORD Pallic soil (Timaru silt loam) to determine how land-use intensification affects indicators of soil quality (macroporosity, bulk density, structural condition score, total and mineralizable carbon and nitrogen and earthworms) and pasture production. The treatments compare irrigated v . dryland pasture and sheep v . cattle grazing on 16 plots. The findings show that soil physical quality responds more quickly to changes in land-use pressure than do biochemical and organic indicators. Both irrigation and cattle grazing, particularly in combination, increased soil compaction; macroporosity on irrigated plots grazed by cattle ranged from 9·1 to 13·3% v/v at a depth of 0–50 mm, compared to dryland plots with sheep grazing (18·9–23·0% v/v). Soil compaction/damage has implications for pasture production, soil hydrology and nutrient movement. Land management practices for intensive cattle grazing of irrigated soil prone to treading damage therefore need to implement high compaction risk strategies to avoid or ameliorate potential changes to soil quality.