Newsletters > Newsletter - January 2010
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Newsletter - January 2010
Grass growth records and predictions.
Below is the average grass growth measured by cage cuts for the last 6 years in the Edgecumbe region compared with growth from a property near Rotorua for the 17 years from August 1989 to 2005.
With what degree of accuracy is it possible to predict monthly grass growth? Based on these figures January growth for the BOP/Rotorua area is expected to be close to 55 kgDM/ha/day. MAF data on hand from the period of 1978 – 1982, largely from the Waikato show average January growth rate of 58 kgDM/ha/day. Whether the January pasture cuts from Edgecumbe for this January are close to average will depend on rainfall in the second half of this month and rain is predicted. Ensuring sufficient feed for stock over the January period given December growth of 62.9 kgDM/ha/day on the Berryman property largely rests on management and soil conditions. In a well-structured soil pasture roots penetrate up to 0.8 m (31 inches). With moisture able to move both up as well as down plants will survive and unless rainfall is markedly less than usual, January production should be close to normal. Well-structured biologically active soils with good levels of carbon have the ability to maintain higher moisture levels than degraded soils with lower levels of carbon. In the November newsletter mention was made of some of the properties we have close contact with entering summer with more feed than others due to having maintained a longer grazing interval throughout spring. We expect the same to apply over the November-December-January period, and although 30 days is an arbitrary figure those able to maintain a grazing interval close to 30 days we predict will survive summer and enter autumn in better shape than those on shorter rounds. The amount of growth in the cages for December has surprised most. The percentage of dry matter from the 6 cages in December was 24%, compared to 14.5% for September growth. Until sufficient rain arrives to lift soil moisture levels to around the ideal 25% the application of fertiliser is unlikely to make any significant difference. What is growing now is the result of inputs and management over the last 90 days. We are often asked whether the application of CalciZest or DoloZest during the summer period results in lessened effectiveness. Our observations along with pasture growth measures and feedback from clients over the last six years indicate no loss of performance if applied during summer. Should a prolonged period of hot dry weather follow an application, initial performance may be lessened. However, given that the applied fungi and bacteria are cultured onto soft carbon and supported with food, applying when practicable is the best option. Making sense of soil tests. With major focus of the fertiliser industry being the sale of phosphorus during the last 30+ years it is not surprising that the Olsen P test, designed to measure plant available phosphorus, has been a focus. For decision making to be better than guessing, measurements are essential. More data usually means the decisions made take us closer and more rapidly to where we wish to go, however interpretation of test results is not always as straightforward as first appears. Following are extracts from the NZ Fertiliser Journal, Autumn 1985 The fertility of a soil, as measured by soil tests, is variable. The variation in soil tests is due to three sources: (a) Laboratory errors. These are generally small in relation to other sources of error and, providing good quality control procedures are used, can largely be ignored. (b) Spacial variation. This includes within-paddock variation and between paddock variation. It can be due to natural causes (eg variation in topsoil depth) or management practices (eg uneven return of dung and urine, past fertiliser practice etc). (c) Variations over time. Changes in soil moisture, temperature and biological activity can affect soil test levels. The time since the last fertiliser application can also affect soil test levels. One way to express this variation in soil test values is as a percentage . From these percentage errors we can calculate confidence intervals for each soil test. What do these confidence intervals mean? Take for example the Olsen P figures. At a mean soil test value of 25 the interval is ± 10. In other words, if you resampled the paddock then 90 times out of 100 the retested value will lie within this range (15 – 35). The retested value may be above or below 25 but, providing it is within this range, the fact that it is different from 25 does not necessarily indicate that the P status of the soil has changed. It may simply reflect soil variability. The Resin P test was introduced by Hill Laboratories in 1993 to complement the Olsen P test to overcome some of the anomalies observed with the Olsen P test. Anomalies with the Olsen P test were observed with soils with low pH, high pH, and recently limed soils. Olsen P target levels also vary with the P retention of soils. We recommend that both Olsen and Resin P tests be requested. Unless major changes are being made to fertiliser programmes testing once every 3 years is recommended. For those particularly interested, or where the history of phosphorus inputs is largely unknown a Total P test provides useful information. Physical soil structures are also an important factor in the supply of phosphorus. In a biologically active well structured soil with plenty of feeding roots below 75mm (3 inches) an Olsen P of 10 can provide maximum pasture yield, however in a degraded soil where plant roots are largely confined to the top 75mm an Olsen P of 30+ may be required to ensure pasture growth is not limited. The information we have indicates that usually somewhere between 3 – 5% of total soil phosphorus is available for plant uptake at any given time. This means that provided soils are well structured, there is a history of phosphorus inputs and soil test levels are somewhere near normal the likelihood of a lack of phosphorus limiting pasture growth over the growing season is highly unlikely. As only a very small proportion of phosphorus is available for plant uptake at any given time, can more of the often up to several hundred kilograms of soil phosphorus within reach of plant roots be made available? The answer is yes and mycorrhizal fungi under the right conditions can be major contributors. The term mycorrhizae means fungus root. These fungi when they invade a plant root have the ability to grow out from the root into the soil up to 15cm (6 inches). The absorptive surface of the root system may increase by up to 10 times that of an uninfected plant and can reach into smaller soil pores than the plant’s root hairs. This allows the plant to absorb significantly more phosphorus and other relatively immobile, and available in only low concentration, nutrients. Mycorrhizal fungi derive a survival advantage from teaming up with plants with the plant providing energy to the fungi. Water uptake may also be improved by mycorrhizae, making plants more resistant to drought. Plants may also receive protection from some soil-borne diseases and parasitic nematodes as a result of mycorrhizal activity. Mycorrhizal fungi are one of the selected beneficial fungi added to CalciZest and DoloZest. The steady increase in energy, measured by brix, increases the efficiency of phosphorus harvesting by plants; just another good reason for the application of DoloZest or CalciZest this autumn. Pastoral
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