Brendon J. Malcolm

OverseerFM is widely used for farm nutrient budgeting in New Zealand. Earlier versions under-predicted cropnitrogen (N) uptake for some crops under moderate to high soil N supply, leaving more residual N in the simulated soil profile and limiting the model’s ability to represent the environmental benefits of catch crops and other cropping systems. To address this, field data from 37 experiments across a range of crop types and regions were used to recalibrate crop parameters. Two updates were introduced: a luxury N uptake factor to represent additional uptake when N supply exceeded baseline requirements, and an iterative monthly coupling between crop uptake and soil mineral N supply. Together, these changes reduced under-prediction of above-ground N uptake and improved agreement withobservations across diverse crops, including reduced prediction error in an independent validation dataset. Soil-mineral-N prediction error also decreased in one rotation dataset, although substantial discrepancies remained. The revised model therefore provides a stronger basis for representing N capture by catch crops, while winter-period uptake and nitrate leaching require further validation.

This review presents a synthesis of current knowledge about managing the potential impacts of outdoor animal wintering activities and their consequences for a range of environmental outcomes. The scope is confined to field‐based wintering approaches and thus, does not consider issues associated with the winter use of animal shelters or standoff systems. Studies that have documented some effects of winter grazing activity are summarised focussing on outcomes for soil condition, nitrogen (N) leaching and contaminant transport via surface runoff. Four key themes are shown to influence environmental outcomes: (i) grazing pressure, (ii) dietary N intake, (iii) landscape vulnerability attributes and (iv) the use of subsequent catch crops. A suite of relevant planning and management considerations are listed that align with pre‐, during‐ and post‐grazing phases of wintering systems. Some initiatives to address remaining knowledge gaps and assess effects that future changes to animal wintering practices may have on environmental outcomes and consequences for the farm system are also provided.

Fodder beet ( Beta vulgaris L.) is an important forage crop used for cattle wintering in New Zealand. Regional nitrogen (N) fertiliser experiments over two seasons (2016–2018) consisting of different N application rates (0–300 kg N/ha) and times of N application (sowing, canopy closure, and mid‐bulb development stage) were used to validate yield responses. Within site, there was a maximum of 3 t DM/ha difference in total biomass yield between control (no N) and high N treatments at maturity. Near maximum fodder beet yield was achieved in all sites with a rate of 100 kg N/ha applied as urea (split applications). Near optimum yields were achieved on higher fertility sites with preseason soil nitrate‐N + ammonium‐N (0–15 cm depth) of 75 kg N/ha or greater. Little additional fertiliser N was required for maximising crop yield. However, enhanced plant N concentration and crop N uptake were achieved with rates up to 300 kg N/ha. Fertiliser N management that stimulated full canopy expansion with optimum green leaf area (GLA) and GLA duration was required to maximise yield. Important management practices for maximising yield include the use of N fertiliser for earlier crop canopy closure and enhanced canopy duration during bulb development.

Winery wastewater (WW) is a high-volume biowaste and, in the context of Marlborough and New Zealand wineries, there is a growing recognition of the need to improve current WW disposal systems to mitigate negative environmental impacts. The application of WW to land is a low-cost method of disposal, that could significantly reduce the environmental risk associated with WW directly entering surface and groundwater bodies. This study analysed elemental concentrations in WW and soils from three Marlborough vineyards across their annual vintage to determine the loading rates of nutrients into WW and the subsequent accumulation effects of WW irrigation on receiving soils. The findings showed loading rates of approximately 1.8 t ha⁻¹ yr⁻¹ of sodium within WW and a significant increase in soil sodium concentration and pH, attributed to sodium-based cleaning products. A loading rate of approximately 4 t ha⁻¹ yr⁻¹ of total organic carbon was also identified within WW, however, significant losses in soil carbon, nitrogen, magnesium and calcium concentrations were identified. Focusing efforts to retain key nutrients from WW within soils could provide benefits to New Zealand’s wine industry, facilitating increased biomass production in irrigation plots, thereby increasing biodiversity and potentially generating incentives for vineyard owners to contribute to increasing biomass carbon stocks and offset agricultural greenhouse gas emissions.

Eight oats catch crop trials were conducted over two years on winter forage paddocks on commercial dairy farms in Canterbury and Southland measuring the effect of tillage and timing‐by‐tillage, respectively, on dry‐matter (DM) yields, N uptake and profitability (gross profit margin). The main objective was to successfully integrate catch crops into winter forage rotations over a critical period when the soil is normally bare and the potential for N drainage loss from urinary‐N deposition is high. Oat harvest yields at green‐chop silage maturity (∼50% panicle emergence) ranged from 8 to 10 t DM/ha when sown by the end of winter (4–5 months after drilling). Nitrogen uptakes ranged from 52 to 363 kg N/ha. Net gross profit typically ranged from NZ$1000 to NZ$1600/ha (assuming revenue of NZ$0.20/kg DM for standing feed). Minimum‐till cultivation produced higher DM yields than direct‐drill treatments in both years of the Canterbury trials (∼30% higher overall) but where N availability and good soil‐seed contact were maintained, differences in yield were small (∼5%). Earlier sowing in Southland using a spader‐drill combination increased DM yields and N uptake overall by 123% and 48%, respectively, over later sown conventional tillage options.

This study tested the effect of oat catch crops on mineral nitrogen (N) leaching losses from cool season fodder beet grazing. Undisturbed soil monolith lysimeters were collected from two grassland sites with soils featuring contrasting texture and water holding capacity (WHC) characteristics. After simulated fodder beet grazing in late autumn or winter, synthetic dairy cow urine was applied. Nitrogen leaching losses were measured from lysimeters sown with oats after urine application and compared with those under fallow conditions until spring. Oat dry matter (DM) production and N uptake measurements were obtained. Sowing oats reduced total mineral N leaching losses by up to 59%. Reductions in mineral N leaching were inconsistently affected by soil type but were strongly influenced by urine application timing. Nitrogen uptake by oats (52–143 kg N ha⁻¹) drove reductions in N leaching losses compared with fallow soil. Oats yielded 4–17 t DM ha⁻¹, and both yield and N uptake were strongly affected by urine application timing (winter > autumn) and soil type (high WHC > low WHC). Sowing oats after fodder beet grazing instead of leaving the ground fallow can reduce the environmental impacts of these systems, while simultaneously increasing annual feed supply. Catch crop gains can be maximised by avoiding or delaying autumn grazing of fodder beet, particularly on low WHC soils.

Residual nitrogen (N) left in the soil following summer cropping or grazing by livestock is at risk of leaching in winter and spring. This study, conducted in Waikato, New Zealand, assessed the performance of different catch crop species and sowing dates in reducing the risk of N leaching. In 2016, Italian ryegrass and oats were sown in late March, April and May. In 2017, Italian ryegrass, oats and triticale were sown in mid March, April and May. In both years, urea fertiliser (400 kg N/ha) was applied immediately before the first sowing to simulate high N loading of the soil following crop grazing. Both years also included a fallow treatment (control) in which no catch crops were established. In both years, catch crops reduced N losses by 11–55% compared with fallow ground. Oats performed the best at earlier sowings, closely followed by triticale, while Italian ryegrass performed better at the later sowing. Sowing in March resulted in the highest reduction in N losses for all species. These results demonstrated that catch crops can be used to reduce N losses in these Waikato systems, and that species selection and sowing date are key to maximise their effectiveness.

(1) Background: Winter grazing of livestock poses significant environmental risks of nitrogen (N) leaching and sediment runoff. (2) Methods: A field study tested the effects of sowing catch crops of oats (Avena sativa L.), ryecorn (Secale cereale L.) or triticale (Triticosecale) in June and August (winter) in Southland, New Zealand (NZ), on the risk of N leaching losses from simulated N loads left after winter forage grazing. (3) Results: Catch crops took up 141–191 kg N ha⁻¹ by green-chop silage maturity (approximately Zadoks growth stage 52; November/December). Importantly, early-sown catch crops were able to capture more N during the key leaching period from winter to mid-spring (77–106 kg N ha⁻¹ cf. 27–31 kg N ha⁻¹ for June and August treatments, respectively). At this time, ryecorn and triticale crops sown in June captured 20–29 kg ha⁻¹ more N than June-sown oats (77 kg N ha⁻¹). In October, early-sown catch crops reduced mineral N in the soil profile (0–45 cm depth) by 69–141 kg N ha⁻¹ through the process of plant uptake. At green-chop silage maturity, catch crop yields ranged from 6.6 to 14.6 t DM ha⁻¹. Highest yields and crop quality profiles (e.g., metabolizable energy, crude protein, soluble sugars and starch) were achieved by the oats, irrespective of the sowing date, indicating that trade-offs likely exist between environmental and productive performances of the catch crop species tested. (4) Conclusion: The catch crop of choice by farmers will depend on the desired end use for the crop, its place in the crop rotation and its potential for an environmental benefit.