P. D. Johnstone

Relationship between pasture dry matter yield and soil Olsen P from a series of long‐term field trials

Abstract Forty‐six data‐sets from a series of 17 long‐term field trials measuring the effects of rates and forms of phosphate (P) fertiliser on pasture production and soil fertility in New Zealand were used to characterise the relationship between pasture dry matter (DM) yield in any year (expressed as relative yield, RY) and soil Olsen P test at the end of the annual DM measurement period. Average coefficients of variation in the measurement of these parameters were 7% and 17% for DM yield and Olsen P, respectively. The results failed to demonstrate that the RY at any site in any year could be reliably assessed from a common relationship between RY and the Olsen P test. However, the mean relationship did take the general “diminishing returns” form as expressed by the Mitscherlich equation, and as Olsen P levels increased the probability of low RY decreased. There was no evidence that RY increased with increase in Olsen P test values above 20, with the exception of the one yellow‐brown pumice soil in the ...

Patterns of, and a model for, dry matter yield response in grass/clover pastures to annual applications of triple superphosphate fertiliser

Abstract Pasture herbage dry matter (DM) responses to annual applications of triple superphosphate (TSP) at 0.5, 0.75, 1.0, and 2.0 times the calculated maintenance requirement were measured in 12 field trials for 6 years. The trials were on well‐established, permanent pastures which had typical fertiliser histories and represented major pastoral soils of North and South Islands of New Zealand. The DM response to TSP averaged over all rates and sites was 5% in Year 1, increasing to 23% in Year 4 with little change thereafter. At individual sites, average responses in total DM over 6 years ranged from 4 to 24%. Responses increased steadily with time at four sites, but at other sites changes with time were erratic. Mitscherlich curves were fitted to the 6‐year total DM production data for each site. However, the standard errors in the parameters of these fitted curves were very large, making it impossible to predict with any useful degree of accuracy the rate of TSP required for any specified yield. Respons...

Changes in soil Olsen P over six years with annual applications of triple superphosphate or reactive phosphate rock (Sechura)

Abstract The effects of annual applications at four different rates of either triple superphosphate (TSP) or Sechura phosphate rock (SPR) on the Olsen P test in soil under pasture were measured over 6 years at 13 sites in New Zealand. Averaged over the 13 sites, TSP applied at the calculated maintenance (M) rate maintained an almost constant Olsen P level throughout the 6 years. However, there were marked differences between sites, particularly at the 2.0 M application rate which at some sites raised Olsen P by over 30 μg P/ml soil but caused no increase at other sites. No obvious explanation such as soil group, phosphate retention, rainfall, or pH, or the TSP rates used could be found for these site differences. Olsen P tests were always markedly lower with SPR than with TSP; averaged over the 13 sites, even the 2.0 M SPR treatment barely maintained the initial Olsen P test values. This difference between TSP and SPR in their effect on Olsen P test contrasted with pasture production data (reported elsewh...

Variations between years in the ram effect when Coopworth or Poll Dorset rams are introduced to seasonally anovular Coopworth ewes

Abstract Seasonally anovular Coopworth ewes previously isolated from rams were joined with either Coopworth or Poll Dorset entire rams for 28 days from either 6 January or 3 February in each of 3 successive years. Induction of ovulation varied between years, and more ewes ovulated when exposed to rams of either breed in February. When rams were introduced in January, more ewes exposed to Poll Dorset than Coopworth rams ovulated within 28 days of ram introduction. Onset of oestrus also varied between years and treatments. It is concluded that the variation in expression of the ram effect is probably governed by depth of anoestrus of the ewes at the time of joining.

Effect of reactive phosphate rock on the pH of soil under pasture

Abstract Soil pH was measured over 6 years in 10 field trials in which superphosphates (SPs) and reactive phosphate rocks (RPRs) were applied annually to clover/grass pastures at rates equivalent to 0, 0.5, 0,75, 1.0, and 2.0 times the estimated amounts of phosphorus (P) required for maintaining near-maximum pasture production. Over the 6-year period, soil pH (0–75 mm soil depth) fell by an average of 0.16 units in control and SP treatments with no significant effect from rate of SP application. RPRs reduced the fall in pH and this effect increased with increasing RPR application rate, the fall in pH being virtually eliminated by the highest RPR application rate. The effect of RPRs on reducing the fall in soil pH could be largely accounted for by the difference in phosphate protonation compared with SPs, and the carbonate content of the RPRs.

Effects of prolonged exposure of ewes to oestrogenic pasture 1. Permanent flock infertility following long-term grazing of red clover (‘Grasslands Pawera’)-dominant pasture

Abstract Romney ewes grazed red clover (P) or mixed red clover/ryegrass (M) pastures for about 6 months/year until mating in Year 4 (P) or 5 (M) of a 6-year study. A further group grazed ryegrass/ white clover (C) pasture continuously throughout the study. At other times all animals grazed ryegrass/white clover pasture as one mob. Ewes grazing P pasture were consistently 3–6 kg heavier than ewes that grazed C pasture. Despite similar proportions of ewes being marked by the ram, and similar ovulation rates, during the first cycle of mating each year, ewes grazing P pastures consistently showed increased returns to service (+30%), increased barrenness (+30%), and fewer lambs born per ewe joined (-0.5) than ewes grazing C pasture. Differences persisted after ewes were removed from treatment pastures, indicating that infertility was likely to be permanent.

Comparison of six phosphate rocks and single superphosphate as phosphate fertilisers for clover‐based pasture

Abstract Six phosphate rocks (PRs), Sechura (SPR), North Carolina (NCPR), Egypt (EPR), Arad (APR), Zin (ZPR), and Nauru (NPR), were compared with single superphosphate (SSP) as annually applied P fertilisers for mown ryegrass/ white clover swards at two sites, in the central North Island (Te Kuiti) and southern South Island (Woodlands) of New Zealand over a period of three years. NPR was finely ground before application but the other PRs were applied as received and so differed considerably in particle size distribution. Measurements were made of annual dry matter (DM) production and % P in harvested herbage, and Olsen P in the soil at the end of each year. Overall, responses were in the order SSP>SPR∼NCPR>APR∼EPR∼ZPR∼NPR. There were important differences in responsiveness to PRs at the two sites. The agronomic performance of PRs was better related to their extractability by formic acid than to extractability by citric acid. Replacement of the standard citric acid test used in New Zealand by the formic ac...

Effects of frequency of application of triple superphosphate and Sechura phosphate rock on pasture DM production, herbage P concentration, and Olsen P soil tests

Abstract Triple superphosphate (TSP) and Sechura phosphate rock (SPR) were applied to developed pastures annually at 0.75 times the estimated annual pasture maintenance requirement (M) and triennially at 2.25 times M in small‐plot trials at 12 sites for 6 years. A control treatment receiving no phosphorus (P) fertiliser was also included. Pasture dry matter (DM) production and soil Olsen P tests were measured annually at all sites and pasture P concentration at two sites. Total DM production over 6 years did not differ significantly between annual and triennial treatments. Triennial applications resulted in higher DM production in Years 1 and 4, similar production in Years 2 and 5, and lower production in Years 3 and 6, compared with annual applications. Averaged over two 3‐year cycles of fertiliser application, the amplitude of the cyclic effect on DM production from triennial as compared to annual application was + 4% for TSP and ± 2% for SPR. Differences in annual production between triennial and annua...

A putative effect of ambient temperature during the rut on time of calving in young red deer hinds

Abstract The principle cue entraining circannual environmental rhythms and reproductive function in red deer is photoperiod, but other factors probably play important roles in modifying seasonality. Examination of calving records of untreated, first‐calving hinds over a 10‐year period revealed year‐to‐year variation in the mean calving date. Most variation was due to individual hinds, however a significant (P < 0.05) influence of the mean minimum temperature during the early rutting period on calving date was apparent with colder temperatures associated with slightly earlier mean calving dates.

Effects of triple superphosphate and Sechura phosphate rock on clover and nitrogen content of pasture

Abstract The effect of annual applications of triple superphosphate (TSP) and Sechura phosphate rock (SPR) on clover content of permanent pasture was measured at seven sites in New Zealand. Clover content as a percentage of total pasture dry matter (DM) production (% clover) increased with phosphorus (P) application rate, and the response of % clover to P increased with time over 6 years. Most of the response occurred at P fertiliser rates up to the mean calculated maintenance rate of 25 kg P/ha per year, with little further response to twice this rate. The response in total pasture DM production to rate of P fertiliser was similar to the response in % clover. Near‐maximum % clover was achieved with Olsen P levels of 12–15. Percentage clover responses to TSP and SPR did not differ significantly at equal rates of P. There was a significant relationship between % clover and % nitrogen in total DM.