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All Posts By

Dr Neil Miles

Nov 19

Stikstofbemesting vir Intensiewe Weidingproduksie

By Nitrogen, Nitrogen Products

English: USE OF FERTILIZER NITROGEN ON INTENSIVE PASTURES Stikstof (N) is die voedingselement wat in die grootste hoeveelhede deur weidingsgewasse uit die grond opgeneem word. Die beskikbaarheid van N en water tesame met temperatuur is gewoonlik die belangrikste faktore wat produktiwiteit van weidings bepaal. Reaksie van weidingsgewasse op toegediende N Die reaksie van weidings op N-bemesting is in verskeie plaaslike en internasionale  navorsingsproewe bestudeer.  In Suid Afrika het die navorsing hoofsaaklik gefokus op die N-behoefte van Raaigrasse, Kikoejoe en Oulandsgras (Eragrostis curvula), terwyl die navorsing op Kropaar, Langswenk en Smutsvinger (Digitaria eriantha) beperk is.  ʼn Tipiese verwantskap tussen N-toedienings en droëmateriaalproduksie vir Kikoejoe word in Figuur 1 aangedui. Toenemende N-peile toon aanvanklik ‘n verwantskap met opbrengs wat amper liniêre is (A), gevolg deur ‘n fase van dalende meer-opbrengs (B) en dan ‘n fase waar hoër N-peile min of geen effek op opbrengs het nie (C). Opbrengs/kg N gedurende fase A is van die tipe weiding, die tempo van beweiding en groeitoestande afhanklik. Die opbrengs/kg N van tropiese weidings is normaalweg hoër as die van gematigde weidings.  Oulandsgras het byvoorbeeld 60 kg/kg N in veldproewe geproduseer terwyl raaigras slegs 25 tot 34 kg/kg N onder besproeiing in dieselfde gebied gelewer het. Die produksie van Meerjarige Raaigras is gemiddeld 23 kg/kg N oor die hele seisoen vir toedienings van 0 – 300 kg N/ha in die Verenigde Koningryk. Die reaksie op N-bemesting vir Meerjarige Raaigras is egter twee tot drie keer hoër in die lente as gedurende ander tye van die jaar. Die reaksie van melkproduksie op toegediende N Die opbrengsreaksie van weidingsgewasse op N-bemesting behoort ideaal gesproke vir ‘n melkboer  in melkproduksie omgeskakel te word. Tipies word een liter melk/kg droëmateriaal of een kg onoplosbare melkbestanddele/15 kg droëmateriaal geproduseer. Die waarde van droëmateriaal is tans nagenoeg R2000/ton in melkboerdery in Suid Afrika. Ongeveer 9 tot 16 kg/melk/kg N bemesting word volgens buitelandse navorsing geproduseer. Hoër syfers in die verband het nie met betekenisvolle verhoging in melkproduksie/koei te doen nie maar wel met die hoeveelheid koeie/ha.  Verskille in reaksie tussen N-bronne Ureum en KAN (kalksteenammoniumnitraat) is die twee belangrikste N-bronne wat op weidings gebruik word terwyl ander soos ammoniumsulfaat in ‘n mindere mate gebruik word. Weidingsgewasse neem beide ammonium-N en nitraat-N op, maar omdat   ammonium (ook die ammonium-N afkomstig van ureum) gewoonlik binne ‘n paar weke na nitraat omgeskakel word, word die meeste N dan ook in die vorm van nitraat-N opgeneem.  Hierdie N-omsetting is egter slegs effektief in goed deurlugte grond wat nie suur is nie by temperature bokant 5°C Effektiwiteitsverskille tussen N-bronne word in ‘n groot mate deur grond en omgewingstoestande beïnvloed. Hierdie verskille hou dikwels verband met verskille in ammoniak vervlugtiging. Navorsing het bewys dat die ammoniakverliese van KAN weglaatbaar min is, ongeag grond en omgewingstoestande.  In teenstelling met KAN kan aansienlike ammoniakverliese met ureum voorkom wat deur die volgende toestande bevorder sal word: Gronde met ‘n pH (H2O) hoër as 6 of waar kalk op die oppervlakte voorkom. Sanderige gronde met lae organiese materiaal inhoud en lae katioonuitruilkapasiteit….

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Sep 24

IDENTIFYING AND ADDRESSING SOIL COMPACTION

By Soil Health

Soil compaction can be a serious yield-limiting factor in crop production, and indications are that this problem is more widespread than is generally perceived. Since compaction is below ground and, thus, not visible, its role in yield decline often goes unnoticed. Soil types Soils vary in their susceptibility to compaction. Research indicates that soils with higher sand and silt contents are more vulnerable to being compacted than loam and clay soils. In addition, the higher levels of organic matter in humic soils reduce their susceptibility to compaction. Causes Management practices that promote compaction include the following: Intensive tillage. Tillage may temporarily loosen the soil; however, in the long-term regular tillage increases the bulk density of soils through the weakening of soil structure and the depletion of soil organic matter. In addition, implements such as the mouldboard plough and disk harrow compact the soil beneath their working depth. Repeated use of these implements can result in the development of plough pans (compacted zones immediately below the ploughed layer (Figure 1, left). Wheel traffic. The wheels of vehicles used to apply fertilizers, lime and other products, harvest crops and pull implements, result in decreases in soil porosity and yield-limiting compaction (Figure 1, right). In the production of annual crops, 60% or more of the soil surface can be trafficked through cultivating, planting, fertilization, herbicide and other chemical applications (Mitchell & Berry, 2001). The in-field traffic associated with maize silage operations and the production of sugarcane frequently results in severe compaction problems (Figures 2 and 3) and associated yield losses. Animal hooves. The role of animals, particularly in intensive grazing systems, in promoting soil compaction is often overlooked. However, although animals are not as heavy as machinery, their weight is applied to the soil in a relatively small hoof-print, and so can cause significant compaction and damage to pastures, thereby decreasing forage yields and animal performance (Figure 4). Importantly, soils are most susceptible to being compacted when they are wet. Unfortunately, timing of farming operations, such as harvesting, fertilizing and rotating livestock, often makes it difficult to exclude machines and animals from soils when wet. Effects of compaction Detrimental impacts of compaction on soil health and plant growth are due largely to the decrease in the proportions of macro-pores in compacted soils. Effects associated with this include the following: Root penetration into compacted soil layers is restricted, and root and biological soil health compromised through water logging and anaerobic conditions in soils. Water infiltration as well as water-holding capacity of soils are reduced, and effective rainfall is diminished through increased runoff. Ponding on the soil surface after rain or irrigation is usually an indication of compaction. Nutrient uptake by roots is poor in compacted soils. This is due to, firstly, limited root development, and secondly, restrictions on the movement of nutrients to roots by mass flow. Yellowing of plants due to nitrogen deficiency is often associated with poor nitrogen recovery by roots in compacted soils. The picture in Figure 2 (left) provides clear…

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Mar 27

CUT FERTILIZER BILLS BY MANAGING MANURE!

By Manure, PLANT & SOIL NUTRITION

Dung and urine are rich in plant nutrients, and clear evidence of this is the accelerated pasture growth where these products are deposited. Each animal is in a sense a “fertilizer spreader”, and farm management practices need to take this into account in order to make the best use of these nutrients and to avoid unnecessary expenditure on fertilizer and lime. Nutrients in dung and urine The feed consumed by animals – be it pasture, hay, silage, TMR or concentrates – is rich in plant nutrients. Only small proportions of these nutrients are used for meat and milk production, with the remainder being excreted in the dung and urine. In the case of dairy cows on pasture, the approximate percentages of N, P and K excreted are shown in Table 1. The total amounts of nutrients excreted by a cow in a year are considerable (Table 2), with the amounts of nitrogen and potassium being the largest. Attaching a rand value to these nutrients underlines the economic significance of the recycling process. It should, of course, be borne in mind that the monetary value reported in Table 2 does not include that of the secondary nutrients, sulphur, calcium and magnesium, or of micronutrients such as zinc, copper, manganese and boron. And there is also the value of the dung in terms of its contributions to soil health (through improving soil organic matter levels, soil structure and biological health). Why the high fertilizer requirements on livestock farms? Given that the removal of plant nutrients from the farm in milk and meat is minimal, why is there an ongoing need for such large amounts of fertilizer in typical livestock operations? In the case of nitrogen, there is a partial explanation, in that large amounts of this nutrient may be lost by leaching from the rooting zone and by volatilization to the air from urine patches. But phosphorus and potassium are not lost in these ways, and one would expect long-term fertilizer requirements for these nutrients to be low on intensive livestock farms. The principal reason for the ongoing high requirement for fertilizers is that because of the movements of animals and feeds, nutrients get depleted from certain areas of the farm and concentrated in other areas. To illustrate this, let’s take a look at nutrient flows in a typical pasture-based dairy-farming operation (which includes silage and/or hay-making). On a farm of this kind, because of the movements of animals and feeds, there are large-scale flows of nutrients from one area to another. These flows are illustrated in the diagram, and result in a concentration of nutrients in areas where animals spend significant amounts of time and are fed (shown in blue), and a depletion of nutrients in more distant areas (yellow), and in particular in those areas in which feed is grown and removed. Plant nutrients are, of course, brought into the system in the form of fertilizers, lime and purchased feeds. Similar nutrient flows occur on intensive beef and sheep operations….

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