Optimale N-bemesting zomertarwe : resultaten onderzoek 2008

In opdracht van LTO en het ministerie van LNV is PPO in 2007 onderzoek gestart naar de optimale N-bemesting van zomertarwe. Hiertoe zijn bemestingsproeven aangelegd op drie klei- en drie zandlocaties met de bedoeling de benodigde datasets te verzamelen om een eventuele aanpassing van het bestaande stikstofbemestingsadvies mogelijk te maken. In 2008 is dit onderzoek voortgezet op 2 klei- en 2 zandlocaties. In dit rapport worden de resultaten van het onderzoek in 2008 weergegeven

Aanpassing N-bemestingsadvies zomertarwe

Door het ministerie van LNV en het Productschap Akkerbouw is aan PPO de opdracht verleend om na te gaan in hoeverre er aanleiding bestaat om voor zomertarwe het stikstofbemestingsadvies in de ‘Adviesbasis voor de bemesting van akkerbouw- en vollegrondsgroentegewassen’ te actualiseren. De conclusie die in deze studie wordt getrokken, is een aanbeveling voor aanpassing van het bemestingsadvies. De analyse is uitgevoerd met de datasets die beschikbaar zijn gekomen door het uitvoeren van bemestingsproeven op zand- en kleigrond in 2007 en 2008. De economisch optimale N-gift is afhankelijk van de kosten voor stikstof en de telersprijs voor tarwe. Zowel de prijs voor stikstof als voor tarwe varieerde de laatste twee jaar sterk. Kunstmest is echter in verhouding duurder geworden dan tarwe, waardoor de optimale economische N-gift lager ligt dan twee jaar geleden toen het onderzoek van start ging. Ondanks deze verandering in prijsverhouding was de economisch optimale N-gift in de proeven hoger dan het huidige advies. Conclusie is daarom dat het bestaande advies geactualiseerd dient te worden. Voorgesteld wordt om voor alle grondsoorten het N-bemestingsadvies met 20 kg N/ha te verhogen

A Buried Drain Erosion and Sediment Loss Control System

The lower ends of most furrow irrigated fields have become convex shaped, meaning the slope progressively increases from a point 20 to 60 feet from the field end to the tailwater ditch. This increasing slope is the result of maintaining tailwater ditches too deep and keeping them cleaned so runoff from these fields is not restricted. The process of forming a convex field end continues yearly at an increasing rate. With each passing year, the slope at the end of the field becomes greater so that runoff water runs faster and has more energy to erode. Over many years, large quantities of soil have been lost from the lower ends of furrow irrigated fields. Field ends 1.5 to 2.0 feet lower than the furrow elevation 20 to 60 feet upslope are common. Much of the soil loss is from the lower ends of fields

Within-Row Irrigation Saves Water on Croplands

Excessive water use and soil erosion from furrow irrigation are two of the most serious management problems on irrigated silt loam soils in southern Idaho, U.S.A. These problems are especially serious on croplands planted to dry beans. In conventional bean production, fields are irrigated before planting to wet the entire soil surface. It is not unusual for farmers to apply as much as 30 cm of water over the entire field during a single preplanting irrigation. Results from this study showed that planting beans in the bottom of pre-irrigated furrows without soaking completely between the furrows reduced preplanting water application by 60%. The continuing within-row treatments reduced irrigation water use by 42% compared to conventional irrigation practices. Total bean yields on the preplanting, within-row treatments were not significantly different from the conventional treatments

A Buried Pipe System for Controlling Erosion and Sediment Loss on Irrigated Land

A new system comprised of a buried pipe, with riser inlets from the surface at intervals, along the lower end of furrow-irrigated fields was designed, installed, and evaluated on 21 fields to determine its effectiveness as an erosion and sediment loss control system for irrigated land. The system utilizes small sediment collection ponds with the riser inlets from the buried pipe serving as overflow outlets for the ponds. This system corrects convex-shaped field ends caused by erosion and solves an energy related erosion problem common on furrow-irrigated land. During the first season, these system removed from 80 to 9S% of the sediment from runoff water and collected from 4.1 to 40.5 Mg ha-¹ from 12 fields on irrigated land where detailed data were collected. All systems performed without problems and all convex end problems except one were corrected the first season. After the convex ends are corrected, the system continues to reduce sediment loss. This new system eliminates the tailwater ditch, puts more land into crop production, reduces weed problems, and prevents the usual problems associated with a wet tailwater ditch. The buried pipe erosion and sediment loss control system is a major advance in the control of erosion and sediment loss on irrigated land

Crop sequences and conservation tillage to control irrigation furrow erosion and increase farmer income

Five years of research show that there are many benefits to conservation tillage on furrow-irrigated land. Benefits are enhanced when cropping sequences are altered to accommodate the fewest number of tillage operations over the entire cropping sequence. Results showed that soil erosion can be reduced 47 to 100 percent, crop yields can be sustained, and farmer net income can be increased an average of more than $125 ha-1 each year over a 5-year cropping sequence

Furrow Erosion and Sediment Losses on Irrigated Cropland

Sediment losses from furrow erosion on irrigated cropland ranged from 0.5 to 142 metric tons per hectare (0.2 to 63.0 tons/acre) on 49 Idaho fields during one irrigation season. Field slope varied from 1.0 to 5.0 percent and furrow stream size from 11.3 to 49.9 liters per minute (3.0 to 13.2 gal/min). Erosion increased sharply on row-cropped fields when slopes exceeded 1.0 percent. Furrow erosion can be reduced by: (a) reducing furrow stream size when water reaches the furrow ends, (b) avoiding irrigation of row crops on slopes that are too steep, (c) keeping the tailwater ditch shallow and the water in it moving slowly, (d) installing tailwater control systems, and (e) alternate-furrow irrigation. Sediment losses from irrigated lands can also be reduced markedly by planting vegetative filter strips and using sediment retention basins. Total phosphorus losses were reduced in proportion to the reduction in sediment losses

Performance of TCP with multiple Priority Classes

We consider the dimensioning problem for Internet access links carrying TCP traffic with two priority classes. To this end, we study the behaviour of TCP at the flow level described by a multiple-server Processor Sharing (PS) queueing model with two customer classes, where the customers represent flows generated by downloading Internet objects; the sojourn times represent the object transfer times. We present closed-form expressions for the mean sojourn times for high-priority customers and approximate expressions for the mean sojourn times of low-priority customers. The accuracy of the model is demonstrated by comparing results based on the PS model with "real" TCP simulation results obtained by the well-known Network Simulator. The experimental results demonstrate that the model-based results are highly accurate when the mean object size is at least 10 IP-packets, and the loss rate is negligible

Furrow Erosion Reduces Crop Yields

Furrow irrigation erosion redistributes topsoil within fields and causes serious topsoil losses from farms. Erosion occurs on the upper portions of fields where the furrow streams are largest and the energy greatest. The furrow stream must be large enough at the head end of the furrow to supply sufficient water for infiltration over the entire furrow length

The Effect of Furrow Irrigation Erosion on Crop Productivity

Furrow irrigation erosion redistributes topsoil by eroding upper ends of fields and depositing sediment on downslope portions causing a several fold topsoil depth difference on individual fields. This investigation was conducted to evaluate the effects of this erosion and deposition process on crop yield and to develop crop yield-topsoil depth relationships. Studies were conducted on 14 farmer-operated fields and on field plots with a continuous topsoil depth gradient from 10 to 66 cm. Severe erosion on the upper ends of fields combined with tillage has mixed light-colored subsoil with topsoil and caused these areas to become whitish in color. Crop yields have sharply decreased on these whitish areas compared to areas where the topsoil depth is 38 cm, or the original depth. Yields were increased, but less sharply, where sediment deposition has increased topsoil depth above 38 cm up to a depth of about 66 cm. Yield-topsoil depth relationships followed the equation Y = a+b 1nX with significant correlation coefficients for wheat (Triticum aestivum L.), sweet corn (Zea mays L.), barley (Hordeum vulgare L.), alfalfa (Medicago sativa L.), dry beans (Phaseolus sap.) and sugarbeets (Beta vulgaris L.). Yield decreases per unit loss of topsoil were greatest for wheat and sweet corn and least for sugarbeets. Yields on whitish soil areas could not be improved more than indicated by these relationships by adding additional fertilizer phosphorus or potassium