J. D. Morton

Soil phosphorus concentrations to minimise potential P loss to surface waters in Southland

Abstract Losses of soil‐derived P in overland flow induced by artificial rainfall were measured from six pastoral soils under a range of soil Olsen P concentrations. These soils were selected as being typical of the major soil groups that cover much of lowland Southland. Our objectives were to establish the magnitude and patterns of soil P release to overland flow under a wide range of soil Olsen P concentrations, established by amendment with either P fertiliser or dairy manure. The incorporation of superphosphate or manure into soils increased the soil Olsen P concentration as well as the concentration of P fractions in overland flow. There appeared to be no difference in the trend of P loss relative to Olsen P regardless of the form of P amendment. The magnitude of P loss appeared to be influenced by soil pedological origin, with lower dissolved reactive P (DRP) concentrations measured in overland flow from the Brown soils, compared to the less weathered Recent and Pallic soils. Regression analyses indicated that DRP concentrations in overland flow exceeded 0.02 mg DRP litre−1 when soil Olsen P values were greater than 51, 24, 10, 9, 5, and 20 mg kg−1 for the Woodlands, Waikiwi, Mataura, Northope, Pukemutu, and Waikoikoi soils, respectively. Given that eutrophication is likely to be encouraged when DRP concentrations in overland flow exceed this value of 0.02 mg litre−1, we suggest that soil Olsen P concentrations should be kept at or as close to the agronomic optimum as possible to minimise potential soil‐derived P losses and still maintain pasture productivity. Economic analysis indicated that significant savings could be made by keeping to the agronomic optimum, avoiding the unnecessary increase in soil Olsen P concentration and consequent increased environmental risk from P loss.

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...

Pasture yield responses to phosphorus, sulphur, and potassium applications on North Otago soils, New Zealand

Abstract Pasture yield responses to phosphorus (P), sulphur (S), and potassium (K) were measured over four to eight years on different yellow‐grey earth (pallic) soils at three non‐irrigated (Timaru, Kauru, and Claremont soils) and one irrigated (Otiake soil) sites in North Otago. Large pasture yield responses to P at application rates up to 80 kg ha−1 yr−1 occurred on three sites with initial soil Olsen P levels of 6–11 μg ml−1, but only a small response up to this rate was measured on the Timaru soil with a higher initial soil Olsen P level (16 μg ml−1). The relationship between soil Olsen P and relative annual pasture yield was similar and moderate (r2 = 0.57) for the average of the three most responsive sites. The highest pasture yield response to S was measured at application rates up to 80 kg ha−1 yr−1 on an Otiake soil with an initial soil sulphate S level of 3 μg g−1. Smaller pasture yield responses at rates up to 40 kg S ha−1 yr−1 occurred on Kauru and Timaru soils with initial soil sulphate S le...

A soil sampling protocol to minimise the spatial variability in soil test values in New Zealand hill country.

Abstract Because of the large inherent changes over time and space, non‐systematic sampling in hill country can result in high coefficients of variation (CV 18–55%) in soil phosphorus (P), sulphur (S), and potassium (K) levels between measurements. The components of spatial variability were measured on 20 hill‐country sheep and beef farms. For Olsen P, 38% of the total farm variance was measured within 1 m of a fixed point, 27% within 100 m, and 35% between paddocks within a farm block. With soil pH, quick test K, and sulphate S, there was greater variation within 1 m, less within 100 m, and very little between paddocks, compared with Olsen P. From this information, a sampling protocol was designed to achieve the target CV for Olsen P (15–20%). The sampling protocol was tested on 77 hill‐country farm blocks. At annual intervals up to 5 years after establishment, 100 m transects from within 3 representative paddocks were re sampled at 10‐m intervals from within a 0.3‐m radius of each original sampling position. All soil cores from the 3 transects except those at each end were bulked (n = 27) for one block. Over 4 years on average, the mean CV for change in Olsen P between years was 21.3%. Corresponding CVs for soil pH were 2.2%, soil sulphate S 37.4%, and soil quick test K 26.2%. These results indicate that the use of a scientifically designed and robustly tested soil sampling protocol will minimise the variability in measured soil Olsen P, pH, and other soil test nutrient levels in hill country over time and allow more accurate advice to be provided on fertiliser nutrient requirements.

The effects of fertiliser iodine application on herbage iodine concentration and animal blood levels

Abstract Two experiments were conducted to evaluate surface applications of potassium iodide and potassium iodate as alternatives to direct treatment of ewes where iodine (I) deficiency may be a problem. In Experiment 1, the hypothesis that grazing of pasture which had been sprayed with a potassium iodide and oil mixture results in increased blood iodine (serum T4) levels in ewes was tested over two years on five farms in Southland and West Otago, New Zealand. The results show that spraying elevated pasture I levels from March to pre lambing. The increased pasture I levels increased serum T4 levels by only 1.5% in late winter, an increase which was not significant (P > 0.05). There were small increases in lambing percentages (1–5%) due to the spraying in both years, but these were not significant (P > 0.05). In Experiment 2, the hypothesis that surface applications of potassium iodide and potassium iodate fertiliser can result in increased herbage I levels was tested on two farms in Southland and West Ota...

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.

Pasture response to soil phosphorus levels measured under mowing and dairy grazing

Abstract Pasture responses to increasing soil Olsen P (phosphorus) levels were measured under dairy grazing and mowing on an allophanic soil (Egmont brown loam) in South Taranaki, New Zealand, for 4 years. Ten farmlet paddocks were allocated to each treatment with average initial soil Olsen P (0–75 mm) levels of 29, 37, 45, 56, and 68 μg P ml‐1 and duplicate mowed plots sited on each of five paddocks. Mean annual pasture production under grazing and mowing, respectively, increased from 16.9 and 13.8 t DM ha‐1 at the lowest to 17.6 and 15.0 t DM ha‐1 at the highest Olsen P. Average spring and autumn pasture P concentrations increased from 0.33 to 0.38% under grazing and from 0.31 to 0.41% under mowing. Increasing Olsen P resulted in small non‐significant increases in average spring and autumn ryegrass contents in both grazing (56 to 63%) and mowing (42 to 45%) treatments. There was no effect of Olsen P on average spring and autumn white clover contents in grazed pastures (8%) but a small increase in mown pastures (8 to 12%). Fitting lines to describe the relationship between Olsen P and the pasture parameters for 4 years grazing and mowing data showed a significant difference (P < 0.05) in slope for spring clover content only. However, there was a large variation in the slope of the fitted lines between years. These results show that although there are differences in absolute pasture production under mowing and dairy grazing, the relative responses to P are not significantly different. Therefore, mowing trials can be used to indicate relative responses in pasture production over the Olsen P range typical of New Zealand dairy farms.

Potassium in soil and pasture and leaching of cations on an allophanic soil in New Zealand

Abstract Potassium chloride (KCl) was applied at 0, 150, 450, and 750 kg ha−1 in May 2000 and April 2001 to an allophanic soil (Egmont brown loam) in South Taranaki to generate a range of soil and pasture potassium (K) levels typical of grazed dairy pastures. Initial mean soil quick test (QT) K levels of 7.0 increased to 7.3, 9.2, 13.6, and 18.5 respectively for each rate of K at the March 2001 sampling. In the March 2002 sampling, soil QT K decreased to 5.5, 7.8, 8.1, and 8.5 for each rate of K. There was only a small effect of rate of K on initial soil magnesium (Mg), calcium (Ca), and sodium (Na) soil QT levels of 30.8, 8.6, and 8.4. Pasture K content was significantly higher (P < 0.05) at the highest rate of K compared with control from July to December in Year 1 (July 2000‐May 2001) and January‐March in Year 2 (July 2001‐May 2002). Increasing rate of K did not significantly change pasture Mg and Ca in most months but significantly decreased pasture Na. Leachate collected at 1 m soil depth showed that with increasing rate of KCl there was a significant increase (P < 0.10) in the amount of leached K in Year 1 ((July‐August 2001) (7.0 kg ha−1 for control to 17.5 kg ha−1 for highest rate of K)), chloride (64.6–146.6 kg ha−1 in Year 1 (P < 0.01), 104.1–202.5 kg ha–1 in Year 2 (June‐August 2002) (P < 0.05)), Ca (30.4–60.1 kg ha−1 in Year 1 (P < 0.05), 34.1–74.3 kg ha−1 in Year 2 (P < 0.10)), and Na (59.4–74.1 kg ha−1 in Year 2 (P < 0.10)). There was no measured significant K effect (P > 0.10) on the amount of Mg, nitrate‐nitrogen and sulphate‐sulphur leached in either year. Therefore, application of excess K fertiliser on allophanic soils to elevate soil QT K >7 will reduce pasture uptake and the availability of Na to animals. If the leached Na and Ca is not replaced, pasture Na and Ca could become deficient for dairy cow requirements.

Balanced and adequate potassium and phosphorus nutrition of pasture

Abstract Pasture production responses from applications of four rates each of potassium (K) (0, 112.5, 225, 450 kg ha‐1) and phosphorus (P) (0, 60, 120, 240 kg ha‐1) in a factorial design were measured in a mowing trial with 60% of clippings returned at a K‐ and P‐responsive site (54.6 μg K ml‐1 and 9 μg Olsen P ml‐1) at Woodlands in Southland, New Zealand over 2 years. There were large significant responses in total pasture dry matter (DM) production to K and P. A bivariate Mitscherlich‐related equation accounted for 97% of the variation in measured values of total DM yield, 94–99% of the variation in ratios of K, P, and nitrogen (N) concentrations in mixed herbage, and 99–100% of the variation in nutrient ratios in white clover, summed or averaged over 2 years. The fitted equations were used to identify combinations of fertiliser P and K rates and ratios of K and P concentrations in mixed herbage and clover that resulted in balanced and adequate nutrition. Two nutrient elements are in balance when the yield response to one added on its own equals the response to the other added on its own, both in relation to the maximum yield. Balanced nutrition in total DM occurred at a K/P ratio of 5.1–7.4 for mixed herbage and 4.2–7.9 for clover, and were highest at higher rates of K and P. For balanced nutrition at 95% relative yield, K/P ratios were 6.8 for clover and 6.7 for mixed herbage. Fertiliser K/ (K + P) ratios for balanced nutrition increased from 0.5 for fertiliser expenditure of