Improving organic potato production systems in Greece; Understanding the influence of variety selection, organic fertilisation and irrigation on potato yield and disease severity

Abstract

Messinia prefecture, is considered to be one of the most important potato production areas in Greece mainly due to its favourable pedo-climatic conditions and availability of irrigation water. The main challenges that organic potato growers are facing are specific diseases (especially late blight), pest (especially nematodes and Colorado beetle) and nutrient management (e.g. availability of suitable organic fertilizers). Furthermore, the main potato variety used in Greece is Spunta, since it is desired by Greek consumers for characteristics such as shape, color, texture and cooking properties. However, Spunta is a variety with low nutrient use efficiency and high susceptibility to light blight. The main objectives of the project reported here was to (a) identify varieties that are more suitable for organic production under the pedo-climatic conditions in Southern Greece and (b) develop improved agronomic protocols (fertilization and irrgigation regimes) in pot and field experiments established in four growing seasons/years. The twelve varieties included in trials were chosen based on existing information on (a) foliar blight resistance and (b) performance in conventional production systems in the spring potato growing season in Greece Results from the study suggest that the variety Sarpo mira may be a sutiable replacement for Spunta (especially for organic production systems) under the pedo climatic conditions in Southern Greece, since it (a) was highly late blight resistant, (b) appeared to be more tolerant to Colorado beetle and (c) produced the highest tuber yield (and mean tuber weights and size) in both field trial seasons, and especially for organic production. Results also showed that fertilisers with a high content of plant available NH4+-N (chicken manure and sheep manure plus agrobiosol) resulted in substantially higher yields than sheep manure and seaweed compost. In pot trials, yields obtained with chicken manure and sheep manure plus agrobiosol were also higher than those obtained with standard mineral NPK fertilisation regimes used in conventional farming practices. Results also suggest that the effect of fertilizer input types on potato health and yield parameters depends on both disease/pest pressure and variety. This study demonstrated that increasing the water input level to approximately 1.5 times the usual amount of water applied to potato crops with standard sprinkler systems will slightly (by approximately 15%) increase tuber yields. Increasing water input levels also resulted in significantly higher late blight severity and the ability to increase yields via improved irrigation protocols therefore depends on the availability of blight resistant varieties such as Sarpo mira. Sprinkler irrigation (which was compared to drip irrigation systems in field trials) was found to be the most efficient irrigation system due to (a) its relatively low cost (compared to drip irrigation), and (b) the ability to reduce foliar frost-damage and (c) the finding that it resulted in lower levels of potato beetle infestation in the field trials. The study reported here showed for the first time that irrigation type has a major effect on Colorado beetle infestation with drip irrigation resulting in approximately 3 times higher infestation than sprinkler irrigation. However, the reasons for this difference are unknown, since the experiments were not designed to assess potential mechanisms. The availability of late blight resistant varieties such as Sarpo mira may therefore allow the use of sprinkler irrigation (a) without substantial losses due to late blight while (b) delivering additional benefits from reduced Colorado beetle infestation/damage. However, additional experiments, in which different varieties are compared under conditions of no or low late blight disease pressure and/or Colorado beetle infestation levels, are required to determine to what extent foliar blight resistance, insect resistance/tolerance and agronomic factors (e.g. differences in soil physical, and nutrient and water supply resulting from contrasting irrigation methods and fertiliser types) have contributed to the yield difference between varieties. Also future studies should focus on investigating the effect of irrigation and fertiliser types on (a) soil nutrient (especially N, P and K) availability release characteristics, (b) root distribution and root system development and (c) soil penetration resistance within the soil profile throughout the growing season.