Plant-soil interactions in reduced tilled organic vegetable systems with agro-ecological service crops - focus on nitrogen dynamics and root growth

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandlingForskning

High nitrogen (N) inputs and intensive soil cultivation are used for adequate organic vegetable production. However, soil tillage operations disrupt soil aggregates and can have detrimental effects on the soil structure. Moreover, increased farm machinery weight results in soil compaction. Therefore, the aim of this PhD project was to gain knowledge on the effect of two alternative management systems on N availability, N leaching risk, vegetable yield and root growth: (1) controlled traffic farming (CTF), where machine traffic is restricted to permanent lanes creating traffic-free vegetable beds and (2) no-tillage with a roller-crimper (NT), where agro-ecological service crops (ASCs) are grown over winter and flattened prior to vegetable transplanting in the spring to contribute to weed control.
Field experiments testing CTF in contrast to random traffic farming were conducted at two Danish organic vegetable farms. Soil mineral N availability was either maintained or increased under CTF two to three years after traffic implementation. Several vegetables showed improved root growth and crop yields under CTF in one out of two seasons, while N leaching risk was not increased, making CTF a promising upcoming production system for organic vegetable production.
The applicability of the roller-crimper as an ASC termination strategy in a no-tillage system was investigated in organic cabbage production in five locations across Northern and Western Europe. The NT system was compared to incorporation of ASCs as green manure and to bare soil. Different ASC species, consisting of pea, cereals, or a mixture of both, were tested as a second factor in three locations. Cabbage yields were reduced under NT management in a majority of cases mainly due to reduced N availability following roller-crimped ASCs. This was the result of three processes: (1) pre-emptive competition by ASCs that accumulated N during their growth, (2) slower N release from ASC biomass at the soil surface and (3) less N release from soil organic matter. Cabbage root growth was either reduced, not affected or increased under NT and was mostly related to cabbage yield response to NT. Root growth reduction under NT was probably caused by more compact topsoil and reduced N availability. Weed growth was suppressed by NT early in the growing season, but was greater later in the growing season, contributing to cabbage yield reduction under NT management. Soil microbial activity was lower in NT than after incorporated green manure, most likely due to the absence of incorporated ASC material and less soil disturbance by tillage.
Cabbage yields after incorporated green manure were comparable to bare soil in half the cases studied here, and were even increased in one case, possibly due to improved N availability. Legume/cereal mixtures released N slower than pure legumes after incorporation, but showed improved weed suppression and reduced N leaching risk, making the species mixture a relevant management tool for organic vegetable production.
Comparable cabbage yields between NT and bare soil were only achieved when pea ASC was employed and fertilization rate was increased. Before NT management can be recommended for organic vegetable production further research needs to focus on the effect of improved fertilization management and long-term implementation of NT, where a non-inversion or more shallow tillage operation, or CTF may be included to compensate for topsoil compaction, while still contributing to a build-up of soil organic matter and soil fertility.
Antal sider142
StatusUdgivet - 14 nov. 2018

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