The Winchmore Trials

If a man empties his purse into his head no man can take it from him. An investment in knowledge pays the best interest – Benjamin Franklin (Morse 1909)

The Winchmore field trials represent some of New Zealand's longest running scientific experiments and, globally, the longest running trials of grazed and irrigated pasture. Since their establishment over 60 years ago, data from the trials have been used in nearly 500 publications (Cousins & McDowell 2012). However, as shown by Rickard & Moss (2012), this is only a partial measure of the trials’ value. More poignant measures include recognition of the role Winchmore played in establishing dairying in Canterbury, the importance of phosphorus (P) and sulphur (S) to soil fertility, and the establishment and management of irrigation systems that underpin much of the rural economy in Canterbury.

The initial aims of the experiments were to (1) establish the response of pasture (white clover/ryegrass) to increasing rates of superphosphate (SSP) and (2) measure the response of pasture to different rates of irrigation at the same rate of SSP. Since P was a major focus of the trials, auxiliary aims were incorporated examining topical issues. These included close examination of the residual treatment that ran from 1958 to 1980 examining the pasture response to the cessation of SSP applications, and the dry matter response to the use of reactive phosphate rock (RPR) instead of SSP.

Not only have the trials fulfilled these aims, but they have continued to answer topical questions. For example, although not seen as a priority when established, the trials have been used to quantify changes in soil carbon (C) over time. Data from Winchmore and elsewhere indicated that, initially, the rate of soil C accumulation in the soil was fast, but it was unclear if the rate had changed beyond that. If, in the long term, the two trials had a finite capacity to store C or indeed were found to be losing C, this would have significant ramifications for the C footprint of New Zealand pastures. Two papers in this special issue (Condron et al. 2012; Scott et al. 2012) are in consensus that, although above ground production was greatly aided by fertiliser and irrigation, there was no difference in below ground soil C stores between treatments. Moreover, the disparity in above and below ground C contents can be explained by a quicker turnover and more bioavailable C present in those treatments receiving SSP and frequent irrigation.

In examining the response of irrigated pasture to SSP applications, Smith et al. (2012) outline several highlights that over 60 years of pasture production data can make possible. These include the response of clover–ryegrass pastures to the cessation of SSP applications. These findings highlight the perils of stopping fertiliser applications suddenly and these must be considered by many when making recommendations when, for instance, the price of P increased by 800% in 2008. Smith et al. (2012) also highlighted the fact that clover will persist and can contribute to productive mixed pastures (11–12 t DM ha⁻¹ y⁻¹) in the long-term without applications of N.

In addressing one of the other aims of the trials, soil P dynamics have been studied extensively (McDowell & Condron 2012). Some of the most significant developments have been made or confirmed with Winchmore data. For instance, in fertilised pastures, the rate of organic P accumulation increases quickly and then reaches a plateau, presumably as all plant-P is supplied from inorganic sources. More recently, the data have been used to answer environmental questions around the loss and role of P in surface water quality. The method of flood irrigation used at Winchmore was shown to potentially lose a great deal of P (up to 7 kg P ha⁻¹ y⁻¹) and that P losses are related to stocking rate more than soil test P concentration (viz. Olsen P) or SSP applications. Coupled with agronomic data, the data from Winchmore trials were also able to show that the potential for P loss increases exponentially beyond a certain point of Olsen P enrichment, and hence exceeding the agronomic optimum represents an unnecessary environmental hazard (McDowell & Condron 2012).

The second aim of the trials was to examine the influence of irrigation on pasture production. Hitherto, the irrigation trial has received much less attention than the fertiliser trial, but nevertheless has been a valuable resource, for instance, in the field of soil biology. Fraser et al. (2012) outline the changes in biotic communities that have occurred in the irrigation trial. They conclude that irrigation to optimise plant growth also optimises (or selects) the invertebrate community. For instance, earthworms tend to migrate down the soil profile when faced with dryness. The effect was mitigated under irrigation, which may partly explain the enhanced soil turnover of nutrients and C noted by Scott et al. (2012).

Perhaps one unforeseen benefit of the Winchmore trials has been the quantification of contaminants associated with SSP applications, specifically cadmium (Cd) and uranium (U). McDowell (2012) found that at the same rate of SSP applications, Cd was enriched in dryland compared with irrigated topsoil, but leached down the soil profile in relation to the frequency of irrigation. Moreover, there was a suggestion that the rate of Cd accumulation had reached a plateau and hence, under the system used at Winchmore, topsoil Cd concentrations were unlikely to exceed the soil trigger value highlighted in the New Zealand Cd management strategy of 1 mg Cd per kg soil.

In conclusion, it has been a privilege to have organised and collated this special issue. It is clear that the Winchmore trials have provided New Zealand agriculture and agricultural science with significant gains. It is up to us to continue to utilise this resource and communicate the scientific discoveries that are sure to come.

The editors and contributors are grateful to the New Zealand Fertiliser Manufacturers’ Research Association, who provided funds to help put this special issue together. We must also acknowledge and thank the many scientists, technicians and farm workers who over the years have maintained the trials, collected and collated data, and ensured that the samples collected have been stored for future analysis as and when required. Perhaps the true value of the Winchmore resource lies in discovering that unknown, as Donald Rumsfeld once said:

Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don't know we don't know. (US Department of Defense 2002)