M. B. O'Connor

Farm dairy effluent: A review of published data on chemical and physical characteristics in New Zealand

Abstract Increased concern about environmental degradation and a move towards sustainable farming systems has lead to closer attention being paid to farm dairy effluents (FDE). Treatment of FDE in New Zealand is mainly through land application, or through oxidation ponds. Since the introduction of the Resource Management Act, 1991, regional councils require dairy farmers to be more accountable for the management of effluent from their dairy farms. Regulations have been imposed to limit the application of nitrogen (N) to land from FDE, and these limits range from 150 to 200 kg N ha‐1 yr‐1. Farmers, consultants, and regional councils require information on the chemical composition, particularly N content, of effluents, so that land effluent application systems can be designed and managed within the guidelines or regulations imposed. Data gathered from previous investigations on effluents in New Zealand found an average solids content of 0.9% dry matter. Between 1977 and 1997 the mean N content of FDE doubled from approximately 200 to 400 mg N I‐1. The trend for higher N concentrations is likely to continue as dairy herd numbers increase. The most likely reason for the increase in N is that volume of washwater used per cow has proportionately decreased as herd size has increased, thus, FDE has become more concentrated with levels above 400 mg N I‐1 increasingly common. Average values of phosphorus (P) and potassium (K) in FDE were 70 and 370 mg I‐1, respectively. Slurries obtained from anaerobic ponds, which require periodic de‐sludging about every 5 years, had average nutrient concentrations of 1650, 290, and 510 mg 1‐1 for N, P, and K, respectively, representing an accumulation of minerals over the 5 years.

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 ...

Pasture production and soil phosphorus fractions resulting from six previous annual applications of triple superphosphate or Sechura phosphate rock

Abstract The effects of six annual applications of either Sechura phosphate rock (SPR) or triple superphosphate (TSP) on pasture production and soil phosphorus (P) fractions were compared at eight New Zealand sites. At most sites, pasture production resulting from residual fertiliser P was significantly (P < 0.05) greater for SPR than it was for corresponding rates of TSP. Molybdenum (Mo) present in the SPR may have contributed to this effect at four of the sites where Mo deficiency was suspected. Sequential extraction (alkali followed by acid) was used to determine chemical forms of residual fertiliser P in soil samples from all sites. Fertiliser P which had reacted with the soil or been adsorbed on soil surfaces was alkali-soluble whereas undissolved apatite residues were acid-soluble. SPR-treated soil had significantly (P < 0.05) higher amounts of acid-soluble P than TSP-treated soil, lower amounts of alkali-soluble P (except at two sites), and higher amounts of total P (except at three sites). The gre...

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...

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.

Sodium requirements for temperate pastures in New Zealand: a review

Abstract Sodium (Na) is not an essential plant nutrient for forage pasture species but is required for optimal animal health and production. The distribution of Na in New Zealand pastures and soils is reviewed and evidence discussed indicating that the incidence of Na deficiency in animals, particularly dairy cows, is likely to increase with time. Vulnerable regions within New Zealand are identified. The results from New Zealand trials confirm that animal production responses to Na supplementation or fertiliser Na are unlikely to occur if the pasture Na concentration is greater than 0.10%. Results from trials examining the effects of Na fertiliser on pasture production and chemical composition are also reviewed. On soils with adequate soil potassium, Na has no effect on pasture production and applications of 50–100 kg NaCl/ha are sufficient to increase pasture Na concentration above the critical level for animal production (0.10% dry matter (DM)), even on soils with low initial soil Na concentrations (MAF Quick Test (QT) <10, 0.20 cmole Na kg−1). Methods for correcting Na deficiency in animals are also reviewed.

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...

Pasture establishment and fertiliser requirements on rehabilitated land after opencast coal mining in New Zealand

Abstract Existing pasture establishment practices to rehabilitate land after opencast mining in the Waikato coal fields area of New Zealand were examined and compared with an alternative method involving different pasture mixtures, seeding rates, and lime and fertiliser requirements. Pasture establishment and production, botanical composition changes, and plant and soil nutrient status were measured during a 2‐year field trial. Highly significant pasture responses were obtained to increased fertiliser inputs. Heavy rates of fertiliser (1000 kg ha−1 superphosphate) were required to raise Olsen P soil levels during the establishment phase whereas half that rate was found to be sufficient for the maintenance phase. An improved seed mixture, containing superior pasture cultivars, established more quickly and out‐yielded the existing seed mixture by 58%. The two seed mixtures responded differently to sowing rates; the higher rate increased pasture yields of the improved pasture species but decreased the existi...

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.