Managing the harvest operation

Transcription

1 Managing the harvest operation Harvesting is a multi-stage operation: Digging (or pulling) the taproot is cut and the plant is inverted, allowing the pods to partially dry Fluffing may be necessary Threshing the nuts are removed from the rest of the plant Pre-cleaning the removal of extraneous material (e.g. dirt, sticks) Drying the crop is usually artificially dried to avoid deterioration of the kernels from the weather. Cleaning out threshers, bins and elevators between seasons is one of the first steps of a successful harvest. One aflatoxin-infected nut left in a thresher can down-grade a whole load. Minimising yield Peg strength, soil and weather conditions, planting date and disease can all cause yield loss at harvest. Peg strength The peg connects the primary branches of the bush to the pods beneath the ground. If the pegs are weak or diseased, they can snap during digging and the pods will remain in the ground. We have found digging dry is better than digging when the soil is too moist. Ian Coventry (Farmer)

2 The most common factors influencing peg strength are overmaturity and disease. If the digger is adjusted and operated properly, a yield loss of five per cent or less should be possible. If the pegs have deteriorated can be considerably higher, even as high as 100 per cent. To check peg strength, dig some bushes out carefully and shake them to simulate the mechanical digging action. If 10 to 20 per cent of the pods fall off, peg strength is declining so consider digging immediately. Do not just pull the plants out of the soil because this does not allow for the loosening action of a cutter blade. Diseases such as leaf spot, rust and net blotch cause defoliation and will also cause pegs to weaken. Soil conditions In hardsetting soils the pegs may break (even when healthy) when the bush is dug from the soil. On these soils, choose one of the runner or Spanish varieties rather than large pod Virginia types such as Middleton. Strategic watering just before digging can soften hardsetting soils and allow easier extraction of the pod. Sandy soils drain quicker than loams and have a wider optimum working range. Machinery is able to work on sandy soil blocks earlier after rain and so harvest delays can be reduced. Heavy rain at harvest on most black soils means high because of delays in digging and soil sticking to the pods, leading to penalties. On heavy soils there is usually a narrow soil moisture window in which to harvest. With the Peanut Company in Tolga having the driers we are not so worried about getting the moisture levels down to the limit. This has helped lower the levels of splits. Nino Quadrio (Farmer)

3 Weather conditions Prolonged periods of rain can cause a loss of yield. Losses are even higher if the bushes have weak pegs due to disease. If rain is likely at harvest, it is better to have the peanuts properly inverted in a windrow than still in the ground. Inverted peanuts shed moisture and dry out quickly. Poorly inverted peanuts in contact with the soil will not dry quickly and can go mouldy if it rains. Late-planted crops The rate of maturity slows down during cool weather in autumn, once the average day/night temperature drops below 18 C. If night temperatures drop below 10 to 12 C, the pods will not mature. Frost will kill the tops of the bushes, making chain or tyre pullers ineffective. Frost can also freeze exposed pods, greatly reducing their quality. If a heavy frost is expected and conditions are then likely to warm up, delay digging until after the frost. This will freeze the tops but not the pods, but the crop then needs to be dug before the bush dies. Diseased crops Crops with high levels of disease may need digging earlier than optimal. In most situations, money spent on fungicides to minimise this problem is justified. Foliar diseases, such as leaf spot, rust and net blotch, can cause the pegs to weaken and break during digging. Diseases like sclerotinia From your contractor you should be buying expertise and capacity. These are the two things that will help maximise the value of the crop. Lionel Wieck (PCA)

4 and white mould attack the stems, causing part or all of the plant to be left behind, thus reducing yields. Harvesting operation cutting and digging fluffing windrow drying threshing measuring moisture content pre-cleaning Cutting and digging Careful digging is critical to the rest of the harvest operation. A good operator working in a weed-free paddock of soft soil can achieve harvest of less than five per cent. The diggers are linkage mounted and cut the taproot below the pods. The machine lifts the bushes from the ground, shakes the soil off, inverts the bushes and lays them in windrows to dry. The cutter blades, which cut the taproots just below the level of the nuts, can be either mid-mounted on a stump-jump framework or attached to the front of the digger. Many diggers in southern Queensland use cutter blades, based on a stump-jump principle, set at 30 degrees to the row. However, most diggers on the Atherton Tableland cut two rows and are based on a solid cutter bar mounted at right angles to the row. Digging should be done with sharp cutters and the speed kept below 5 km/hr.

5 Losses occur if the blades are run too shallow. Keep the blades sharp and set them to penetrate the soil at the same depth for heel and toe. A slight forward pitch will lift the plants and loosen the soil around them, which will reduce the chances of pegs breaking. Dull blades will not cut the root cleanly and may drag the bush, losing peanuts in the process. The three main digger types are: Tyre puller rotating tyres grab the top of the bush and pull it out of the soil after the taproot has been cut Chain puller similar to a tyre puller except that parallel chains grab the top Elevating digger inverter (e.g. KMC) cutter bar cuts and lifts the crop onto an elevator system before inverting the bushes. Figure 1. The taproot is cut and the peanuts inverted in a windrow to dry Care is needed with all types of diggers to avoid leaving pods behind. Synchronise the ground speed with the speed of the elevator chains or belts. Peanuts should drop to the same place from where they were lifted. Speeds over 5 km/h may jerk the plants from the soil and cause.

6 Fluffing A peanut fluffer has elevating chains (similar to the KMC digger) but no blades. The elevator bars pick up the dug windrow, shake out loose dirt and replace the windrow on the ground. The fluffing action improves airflow within the windrow and allows more even drying. Fluffing is used to remove dirt from the windrow within 24 hours of digging or to fluff the windrow after heavy rain. Fluffing after rain is best done in the early morning or the evening when there is dew on the bushes. This ensures pod are kept to a minimum. Windrow drying Peanuts contain 40 to 50 per cent moisture when they are dug. They need to dry down to 16 to 20 per cent in the windrow, which generally takes 2 to 7 days. Leaving peanuts in the field to dry down to a safe storage moisture of 13 per cent is risky, as damage from rain, birds and over-drying can occur during the 7 to 14 days it takes to dry down to this moisture content. Invert the bushes, making sure the pods do not touch the ground, to ensure rapid and even drying. If it rains before threshing, wellinverted crops will dry quickly. Under very hot conditions, peanuts on the soil surface may develop off-flavours or be more susceptible to damage during processing. Some diggers invert the crop better than others, depending on bush size and shape. Some diggers have inverting rods or rake wheels, but these can mix the windrows up rather than leaving the pods Figure 2. Inverted peanuts. Inverting the peanuts correctly will enhance drying quickly and reduce aflatoxin development at this stage After cutting, fluffing within 24 hours certainly knocks the soil out before it sets hard on the nuts. Wayne Weller (Farmer)

7 on top and put soil and rocks into the windrow. Rakes are useful in dryland crops for putting several rows into one windrow. Windrows should be uniform, fluffy and well-aerated. Hilled-up crops may need a levelling chain or bar underneath the digger. This will fill in the hollow so the thresher can easily pick up the windrow. A well-inverted crop makes threshing easier and ensures a cleaner sample, free from sticks, stones and dirt. If heavy rain falls and the leaves become sealed to the soil, the windrow may need to be lifted just before threshing. This is called fluffing and the lifting is similar to an elevating digger, but without the inverter. A rod weeder run just on the soil surface will also do a good job of breaking the soil-plant contact. Pod under these conditions can be high, so extreme care is needed when re-working the windrow and it should be done only if absolutely necessary. Spanish varieties are less susceptible to when re-worked. Figure 3. The crop is threshed once the peanuts have partially dried, leaving the plant residue (leaves and roots) in the field Threshing Threshing at high moisture content and then artificially drying the kernels minimises weather damage and is essential for consistent production of good quality peanuts. Rain can start mould growth when the moisture is less than 20 per cent. Harvest irrigated areas separately from dryland areas. This may mean turning in the middle of a row if the irrigator does not reach the whole paddock. Drought-stressed peanuts on the ends of the

8 row are more likely to have aflatoxin. Mixing peanuts from these ends of rows is a common way to end up with aflatoxin-positive loads from irrigated crops. Modern threshers will remove peanuts from the bush under almost any conditions. However, the settings on the thresher can affect yield, quality, germination and flavour. Set the thresher to remove all peanuts from the bush without smashing the bush. Excessive action breaks the bushes into short pieces, so that instead of passing over the sieves, they fall through with the peanuts and overload the cleaning screens. Excessive drum speed has the greatest effect on quality, causing physical damage to the kernels (Table 1). This effect is much more severe when threshing peanuts at low moisture. Check the settings several times a day, as conditions change. Air conveyers on the thresher can cause the shells of dry peanuts to crack if the fans are operated too fast or the dampers are not adjusted properly. Use only enough air velocity to lift the peanuts into the bin. The air velocity for the cleaning screens also needs frequent checking and adjustment. Use just enough air to blow trash and pops, but not good peanuts, out of the machine. Some threshers are modified so the straw is dropped into windrows to make hay baling easier.

9 Table 1. Effect of thresher cylinder speed on shell damage, loose shell kernels (LSK) and germination Cylinder speed Hull damage (%) LSK (%) Germination (%) slow medium fast Source: Producing high quality seed peanuts, 1990, The University of Georgia College of Agriculture, USA. Peanuts can certainly be threshed at moisture levels well above 25 per cent, but the extra cost and time to dry the crop may offset any advantage. Also, peanuts threshed at very high moisture content can suffer mechanical damage if the thresher has to operate at very high internal speeds. We use the pivot irrigation system to actually wash the soil off the peanuts. Patrick Jones (PCA) If peanuts are allowed to dry to below 16 per cent in the field, the pick-up percentage drops and the thresher may damage more kernels. The cost of losing pods and quality during threshing when below 16 per cent is likely to be more than the cost of drying. In a test at Kingaroy, threshing at low moisture levels increased the amount of split and bald kernels (Table 2). Drying the crop too fast, even after threshing at high moisture, increased the number of split and bald kernels.

10 Table 2. Windrow curing time and curing speed effects on split and bald kernels Days in windrow Threshing moisture Curing speed Split (%) Bald (%) air only slow (3 days) fast (11 hours) Source: A. Baikaloff, unpublished data Measuring moisture content The moisture content of peanuts for threshing, intake and payment is made on a nut-in-shell basis. Determine moisture content on the farm using various portable moisture meters, e.g. the Marconi or Dickey John Moisture Meter. Grind a sample of shells and kernels in a kitchen blender and use the moisture meter to measure moisture content by following the operating manual for the meter. Pre-cleaning Figure 4. Pre-cleaning occurs on-farm Pre- cleaning the load prior to delivery reduces the amount of extraneous material (dirt, sticks etc) in the load. Pre-cleaning removes many of the small immature pods that are high in moisture and so can reduce the overall moisture of a load. Pre-cleaning improves quality and reduces drying and freight costs.

11 Information contained in this publication is provided as general advice only. For application to specific circumstances, please seek professional advice. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate enquiries to determine whether new information is available on the particular subject matter. The State of Queensland, Department of Primary Industries and Fisheries (2007). Address enquiries to or phone