Mark Shepherd

Effect of soil type and rainfall on dicyandiamide concentrations in drainage from lysimeters

The nitrification inhibitor dicyandiamide (DCD) is mobile in drainage water, which has implications for its effectiveness in reducing nitrate leaching from urine patches. Lysimeters had been used to investigate the effect of soil type (clay, silt loam, or sandy loam) and precipitation (target ~1140 or 2280 mm/year) on the effectiveness of DCD to decrease nitrate leaching. This paper reports the associated effects on DCD in drainage water. DCD was applied in May and July at a rate of 10 kg/ha, and natural rainfall was supplemented with irrigation to ensure that the target precipitation was achieved for each treatment. The experiment was undertaken twice. The pattern of DCD concentrations in drainage water suggested that movement of DCD in the silt loam and sandy loam soils was typical of convective–dispersive flow. Although there was some preferential flow of DCD from the soil surface to depth in the clay soil, DCD concentration profiles suggested that the main transport mechanism was also by convective–dispersive flow. There were significant soil-type and precipitation effects on DCD leaching (P < 0.05). The soil-type effect could be attributed to differences in drainage volume between soils. Combining data from the two experimental years, DCD leaching losses ranged from 12 to 46% of applied, with annual drainage in the range 422–1292 mm. DCD was detected in drainage up to 15 months after application, demonstrating the longevity of the compound. The experiment demonstrates that leaching of DCD on all of the soil types tested can be substantial under high rainfall. This is likely to have implications for the effectiveness of DCD to decrease nitrogen losses from urine patches under such rainfall conditions, as well as being a source of nitrogen itself.

Describing N leaching from urine patches deposited at different times of the year with a transfer function

A transfer function (TF) was developed to assist with the estimation of nitrogen (N) leaching from urine-affected areas in grazed pastures. The proposed TF uses a simple function to describe the likely breakthrough curve for urine-N deposited in different months and in various climates and soils in New Zealand. The TF was designed to be integrated into the OVERSEER® Nutrient budgets model to increase the sensitivity of N leaching to the month of urine deposition, but could also be used in any other model that estimates the water balance and plant N uptake on a monthly basis. The inputs required for the TF are typically readily accessible (e.g. soil texture data) and thus do not add any significant complications when added to OVERSEER. The TF retains OVERSEER as the arbitrator of the main items of N-balance in the farm system, but adds functionality by giving a better temporal discrimination of leaching from the farm system. The procedure for parameterising the TF from a comprehensive set of APSIM (Agricultural Production Systems Simulator) simulations is described. Validation of the leaching estimated by the TF was achieved through a combination of testing against an independent set of APSIM simulations and testing against experimental data. The testing of the TF showed very promising performance. The TF explained 75% of the variability of N leaching simulated by an independent APSIM dataset and agreed well with the experimental data.

Application of carbon additives to reduce nitrogen leaching from cattle urine patches on pasture

Abstract A lysimeter experiment evaluated the use of sawdust or sucrose to decrease nitrogen (N) leaching from newly deposited urine patches to a perennial ryegrass/white clover pasture on sandy loam soil. Cow urine (equivalent to 500 kg N ha−1), labelled with 15N-urea, was applied to the surface of lysimeters and sawdust (9 t ha−1) or sucrose (3, 12 or 24 t ha−1) was applied immediately afterwards. Sawdust did not decrease mineral N leaching compared with urine-only (82 kg N ha−1). Sucrose applied at 12 or 24 t ha−1 decreased mineral N leaching by 27 or 66%, compared to urine-only. Pasture dry matter yields were decreased in all sucrose treatments (range 16–29% over 247 days, but 15–73% over the first 70 days) compared with urine-only. Total recovery of 15N in pasture and soil was similar across treatments (average 66%) but the 15N partitioning between soil and pasture differed; soil recovery was 19% in the urine-only and urine + sawdust treatments, and 27–51% in the sucrose treatments, increasing with increasing rate of sucrose. In the farm situation, the risk of yield loss and the large carbon applications required may limit the practical application of this N mitigation method.

An assessment of the effects of fertilizer nitrogen management on nitrate leaching risk from grazed dairy pasture

Dairy farms are under pressure to increase productivity while reducing environmental impacts. Effective fertilizer management practices are critical to achieve this. In the present study the effect of timing and rate of nitrogen (N) fertilizer application on pasture production and N losses, either via direct leaching of fertilizer N or indirectly through consumption of N in pasture and subsequent excretion via dairy cow grazing, was modelled. The Agricultural Production Systems Simulator (APSIM) was first tested with experimental data from N fertilizer response experiments conducted on a well-drained soil in the Waikato region of New Zealand. The model was then used in a 20-year simulation to investigate the effect of fertilizer management on the impacts on potential N leaching losses. Year-to-year variability was assessed by incorporating 20 years of climate data into the model. Modelling indicated that N fertilization at rates of 140 and 220 kg N/ha/year, applied in four split applications and avoiding application in winter months, could increase pasture yield on average by 2·2–3·0 t dry matter (DM)/ha (25–38%). There were some significant amounts of direct leaching in some years, related to environmental conditions. The maximum loss was as high as 61 kg N/ha at an N application rate of 220 kg N/ha/year, in a year with low pasture production and high rainfall following fertilizer application. In general, however, the risk of direct N leaching from applied fertilizer was low. It seems the main effect of N fertilization is to increase the risk of indirect N leaching, due to increased N intake and excretion. The modelling indicated that the major contribution to increased indirect N leaching risk was from the extra DM grown (more urine deposited per ha). Increased N concentration in the pasture due to fertilization and the resultant extra partitioning of excretal N to urine had only a minor effect on indirect leaching losses. The exception was N fertilizer applied in late winter/early spring (July), where fertilizer N (55 kg/ha) increased pasture N concentration by c . 25%, suggesting that the N concentration in urine patch areas could increase from c . 550 to 840 kg N/ha. Further measurements are required to test the hypothesis developed from the modelling that the main effect of N fertilizer on urinary N leaching is by increasing DM production rather than increasing pasture N concentration.

Evaluation of refractive index for measuring urinary nitrogen concentration in a sensor worn by grazing female cattle

ABSTRACT A urine sensor has been developed to measure the volume and nitrogen (N) concentration of individual urination events from female cattle in the field. The objective of this paper was to establish that the sensor’s refractive index (RI) value could be used to accurately estimate urinary-N concentration. Individual urine samples (168 in total) were collected from 18 cows that were fed monocultures (ryegrass, clover or turnips) or from cattle that grazed conventional mixed pasture (ryegrass/white clover) in the field. Regression analysis of urine sensor RI values with either urinary-N or potassium (K) concentrations yielded strong linear relationships (P < 0.001) for all feed types. However, individual regression lines varied between feed types, particularly for turnips. We conclude the use of RI in the sensor provides an accurate estimate of urinary-N but site-specific calibration of the sensor is warranted due to different feed types affecting urine K:N ratio and, by inference, other aspects of composition.

Fertiliser and seasonal urine effects on N2O emissions from the urine-fertiliser interface of a grazed pasture

Significant areas of ruminant-grazed pastures are simultaneously covered by excreted urine and fertiliser nitrogen (N). However, the effect of overlapping N inputs on nitrous oxide (N2O) emission factors has not been studied. Three rates of 15N-labelled urea fertiliser were applied with either no urine, an autumn-urine or a spring-urine application. These treatments were applied to perennial ryegrass pasture (Lolium perenne L.) and N2O fluxes were determined over 373 days using standard static closed chamber techniques. Cumulative N2O-N fluxes ranged from 766 to 4332 g N2O-N ha–1 (0.36%–0.74% of total N applied) and were lowest in the absence of urine; however, no fertiliser rate effect occurred regardless of urine presence or season of application. Urine-elevated N2O-N fluxes followed urine applications for up to 40 days, resulting in lower fertiliser contributions to the N2O-N fluxes at these times. Total 15N recoveries as N2O-N were ≤0.04% and did not differ with fertiliser rate.

Plant N uptake in the periphery of a bovine urine patch: determining the ‘effective area’

ABSTRACT The extent to which the wetted soil area of a urine patch influences surrounding pasture is relatively unknown. The study objective was to use 15N tracer to quantify pasture N uptake in the ‘wetted’ and periphery areas of a spring deposited bovine urine patch over 311 days. Ruminant 15N enriched urine was applied to soil creating a circular wetted area, ‘zone A’ (800 kg N ha−1), with and without urea fertiliser (35 kg N ha−1). Pasture yields, 15N recovery and soil inorganic-N dynamics were monitored from zone A and two peripheral zones, B and C. Fertiliser had no effect on cumulative urinary 15N recovery in pasture (50%–52%). Average cumulative pasture 15N recovery in zones A, B and C were 30.6%, 17.3% and 4.2%, respectively. Soil inorganic-15N recovery occurred in zones A and B, declining with distance from the wetted area. The results suggest an effective urine patch area of 0.95 m2 or 3.4 times the wetted area.

Lateral spread affects nitrogen leaching from urine patches

Nitrate leaching from urine deposited by grazing animals is a critical constraint for sustainable dairy farming in New Zealand. While considerable progress has been made to understand the fate of nitrogen (N) under urine patches, little consideration has been given to the spread of urinary N beyond the wetted area. In this study, we modelled the lateral spread of nitrogen from the wetted area of a urine patch to the soil outside the patch using a combination of two process-based models (HYDRUS and APSIM). The simulations provided insights on the extent and temporal pattern for the redistribution of N in the soil following a urine deposition and enabled investigating the effect of lateral spread of urinary N on plant growth and N leaching. The APSIM simulation, using an implementation of a dispersion-diffusion function, was tested against experimental data from a field experiment conducted in spring on a well-drained soil. Depending on the geometry considered for the dispersion-diffusion function (plate or cylindrical) the area-averaged N leaching decreased by 8 and 37% compared with simulations without lateral N spread; this was due to additional N uptake from pasture on the edge area. A sensitivity analysis showed that area-averaged pasture growth was not greatly affected by the value of the dispersion factor used in the model, whereas N leaching was very sensitive. Thus, the need to account for the edge effect may depend on the objective of the simulations. The modelling results also showed that considering lateral spread of urinary N was sufficient to describe the experimental data, but plant root uptake across urine patch zones may still be relevant in other conditions. Although further work is needed for improving accuracy, the simulated and experimental results demonstrate that accounting for the edge effect is important for determining N leaching from urine-affected areas.

How to Get Published in JSFA.

There is no doubt that the number of papers submitted to journals year on year is increasing and it is a testament to the popularity of JSFA that submissions now regularly exceed 3000 per year, a number that has doubled in the last 5 years. While it is fantastic that so many researchers are keen to publish their findings in JSFA, this inevitably has consequences for the workload of editors and referees, and resulting effects on publication times. As a result, the Journal will be working hard in the next year on expanding to meet this demand. Another consequence of this enormous increase in submissions to a journal that still has a limited number of pages is that only a small proportion of these can be accepted for publication. There is, however, a great deal that authors can do to improve their chances of being published. It’s our experience that a significant number of submissions are out of scope for the journal. We’ve tried to minimize this by publishing a more comprehensive Aims and Scope for authors (onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291097-0010 /homepage/ProductInformation.html). Nevertheless, about 80% of authors will be disappointed when they submit a manuscript to JSFA. In some cases, there are specific problems or limitations to the submissions that could have been corrected either in the experimental design or in the preparation of the manuscript that would have made a big difference. Below are some of the problems we frequently see, and suggestions on how they might be avoided:

The effect of drought and nitrogen fertiliser addition on nitrate leaching risk from a pasture soil; an assessment from a field experiment and modelling: Effect of drought and N fertiliser on nitrate leaching risk

BACKGROUND A combination of field experiment and modelling tested the hypothesis that dry summers increase the risk of nitrogen (N) leaching from pasture owing to a combination of: soil N accumulation in a dry summer; slow recovery of drought-affected pasture in the autumn; and the resultant inefficient use of fertiliser N by the pasture. RESULTS In the experiment, pasture response to urea and apparent N recovery in autumn after the drought was half that of irrigated pasture (7 vs 13 kg dry matter kg-1 N; 28 vs 52% apparent recovery; P < 0.05). There was more soil mineral N at the start of drainage (P < 0.001) as a result of this inefficient fertiliser N use. Modelling of pasture growth in six different drought years demonstrated that subsequent N leaching risk after rewetting was inversely related to pasture N uptake during rewetting in the autumn. CONCLUSION When the period between post-drought pasture recovery and the onset of drainage is short, N leaching risk increases. Nitrogen leaching is determined by the type of autumn (slow or fast growing conditions before drainage) and the amount of fertiliser N applied. The latter can be managed by a farmer, but the former cannot.