Root development in potato and carrot crops – influences of soil compaction

Row crops such as potatoes (Solanum tuberosum L.) and carrots (Daucus carota L.) are of high economic value in the Nordic countries. Their production is becoming more and more specialized, including continuous arable cropping and heavier farm machinery, with increased risk of soil compaction. The result may be restricted root development and economic losses. Potatoes have widely branched adventitious roots, whereas carrots have taproots with fibrous roots extending from them. Under optimal soil conditions, total root length per surface area may reach more than 10 km m^?2 for both species. Maximal root depth is about 140 cm for potato and more than 200 cm in carrots. Most of the root mass is usually distributed within the upper 100 cm, whereof more than 50% may be deeper than 30 cm. Soil compaction causes a dense soil with few large pores, poor drainage and reduced aeration, especially in wet soils with low organic matter content and high proportions of silt or clay. With compacted subsoil layers, roots will be concentrated more in the upper layers and thus explore a smaller soil volume. This will lead to reduced water and nutrient uptake, reduced yields and low nutrient utilization efficiency. In this review article, we describe the interactions between root development and soil conditions for potatoes and carrots, with special focus on sub-optimal conditions caused by soil compaction. We also discuss the effects of tilling strategies, organic material, irrigation and fertilization strategies and controlled traffic systems on root and yield development. To reduce subsoil compaction there is a need to implement practises such as controlled traffic farming, new techniques for ploughing, better timing of soil operations, crop rotations with more perennial crops and supplements of organic material. Moreover, there is a need for a stronger focus on the impacts of farm machinery dimensions.     

Effects of Algal Fibre and Perlite on Physical Properties of Various Soils and on Potato Nutrition and Quality on a Gravelly Loam Soil in Southern Norway

Large quantities of seaweed are harvested world-wide for industrial processing, but significant amounts of by-product remain unused and may cause environmental pollution if returned to the sea. Its potential for use in agriculture is therefore of interest. Algal fibre waste from a large alginate extraction plant in Norway was studied with respect to its potential both for soil physical amelioration and as a nutrient source for potatoes. The material contained perlite, itself a wellknown growth substrate, as this was used to filter the fibre in the factory. The effects on soil moisture retention and aeration properties of incorporating up to 80% fibre waste or pure perlite were studied on five widely contrasting soil types. The algal fibre waste had similar effects to pure perlite on soil aeration and on the proportion of water held at low soil moisture tension. It had, however, a far greater effect on moisture retention at higher tension levels. Plant-available water increased by 3.6 vol.% when 10% by volume of fibre was incorporated, as against 1.2 vol.% with the same volume of pure perlite. The effects were similar in all soils. The effect on potato growth and quality of spreading 20 or 40 Mg ha -1 of algal fibre was studied by comparison with the use of various amounts of compound nitrogen- phosphorus-potassium (NPK) fertilizer. The algal fibre contained large amounts of plant nutrients. In the absence of fertilizer, potato yield increased by 30% and 70% with the use of 20 and 40 Mg ha -1 , respectively. These increases declined to 7% and 17% at the highest rate of fertilizer application (120 kg N, 55 kg P and 187 kg K ha -1 ). The effect of 10 Mg ha -1 algal fibre was equivalent to that of 20-25 kg N in compound fertilizer. Algal fibre had little effect on soil contents of available P, K, calcium and magnesium, but the level of sodium rose sharply. Electrical conductivity did not, however, rise excessively. A considerable amount of mineral N remained in the soil after harvest, but most was lost to leaching before the following year's ryegrass crop could make use of it.     

Comparison of crop and weed height,for potential differentiation of weed patches at harvest

Weeds and weed control are major production costs in global agriculture, with increasing challenges associated with herbicide‐based management because of concerns with chemical residue and herbicide resistance. Non‐chemical weed management may address these challenges but requires the ability to differentiate weeds from crops. Harvest is an ideal opportunity for the differentiation of weeds that grow taller than the crop, however, the ability to differentiate late‐season weeds from the crop is unknown. Weed mapping enables farmers to locate weed patches, evaluate the success of previous weed management strategies, and assist with planning for future herbicide applications. The aim of this study was to determine whether weed patches could be differentiated from the crop plants, based on height differences. Field surveys were carried out before crop harvest in 2018 and 2019, where a total of 86 and 105 weedy patches were manually assessed respectively. The results of this study demonstrated that across the 191 assessed weedy patches, in 97% of patches with Avena fatua (wild oat) plants, 86% with Raphanus raphanistrum (wild radish) plants and 92% with Sonchus oleraceus L. (sow thistles) plants it was possible to distinguish the weeds taller than the 95% of the crop plants. Future work should be dedicated to the assessment of the ability of remote sensing methods such as Light Detection and Ranging to detect and map late‐season weed species based on the results from this study on crop and weed height differences.     

Evidence that resistance to potato leafroll virus accumulation in tetraploidsolarium tuberosum L. is controlled by one or few major genes that are not complementary

Summary Previous investigations into the inheritance of resistance to accumulation of potato leafroll virus indicated a dominant major-gene effect, but the segregation ratios in progenies of crosses were a closer fit to a model involving two complementary genes (both required for resistance and one present in the susceptible parent cultivar, Maris Piper) than to a single gene model. In this study, we tested the complementary gene hypothesis by backcrossing susceptible segregants from one of these progenies to their susceptible parent, Maris Piper. No resistant segregants were found in the five backcross progenies examined, so the complementary gene hypothesis was not supported. There was significant variation between susceptible progeny-members in these backcrosses. The progeny of another, highly resistant parent clone, G. 8107(1), selfed, was also examined: all members were resistant. Whilst there is evidently a dominant major-gene effect involved, this is not the whole picture and there are other unidentified genetic effects.