Lille effekt af fangafgrøder

Økologisk produktion af salgsafgrøder uden tilførsel af fosfor (P) eller kalium (K) vil med tiden kunne begrænses af næringsstofmangel, ikke mindst i afgrødernes etableringsfase, hvor de har et lille rodsystem. Hvor lang tid der går før problemet opstår, afhænger blandt andet af jordens næringsstof status ved omlægning til økologi. Vi ved at efterafgøder kan være et godt redskab til at flytte rundt på tilgængeligt kvælstof (N) i et økologisk sædskifte, men gælder det også P og K når jordens status bliver lav? Dette har vi undersøgt i FØJO-II projektet VegCatch med titlen "Økologiske grønsager og efterafgrøder"

A model analysis on nitrate leaching under different soil and climate conditions and use of catch crops

The use of crops and catch crops with deep rooting can strongly improve the possibility of retaining nitrate-N that will otherwise be leached to the deeper soil layers and end up in the surrounding environment. But will it always be an advantage for the farmer to grow a catch crop? This will depend on factors such as soil mineral nitrogen level, soil water holding capacity, winter precipitation, rooting depth and N demand of the scceeding crop. These factors interact, and it can be very difficult for farmers or advisors to use this information to decide whether growing a catch crop will be beneficial. To analyse the effect of catch crops under different Danish soil and precipitation conditions, we used the soil, plant and atmosphere model Daisy

Mere optimal udnyttelse af forfor og kalium i såvel jord som alternative gødningskilder

Med målet om at udfase brugen af konventionel husdyrgødning og halm vil det blive sværere at sikre næringsstoffer til økologiske afgrøder. Mange økologiske landmænd tilslutter sig principielt beslutningen om udfasning, men bekymrer sig samtidig om det nu lader sig gøre at sikre en tilstrækkelig forsyning med fosfor og kalium i fremtiden. Situationen giver anledning til seriøst at vurdere hvorledes sikrer man en optimal udnyttelse af jordens eksisterende reserver? Og bør økologisk jordbrug overveje nogle af de alternative gødningskilder, der pt. ikke udnyttes

Catch crops have little effect on P and K availability of depleted soils

It is a well-known fact that catch crops have a significant effect on availability and loss of soil inorganic nitrogen (Thorup-Kristensen et al., 2003) and recently marked effects on soil inorganic sulphur dynamics have also been shown (Eriksen and Thorup-Kristensen 2002; Eriksen et al., 2004). However, we know much less about the effect of catch crops on phosphorous (P) and potassium (K) mobilisation and availability for the next crop. After several years of organic cash crop production, e.g. vegetables and cereals, yield levels may gradually be limited by soil P and K availability, depending on the initial status at conversion to organic production principles. This is particularly the case during the establishment phase of certain vegetable cultures with a limited rooting system (e.g. lettuce, leeks, onions). Therefore, it has often been hypothesized that certain catch crops are capable of increasing the availability of P and K when the soil status becomes low. In the VegCatch subproject 'Catch crops as a tool for increasing P bioavailability in soils' we have therefore studied the ability of different catch crop species to mobilise and take up P and K from soils of low availability, as well as the ability of the catch crops deliver P and K to the subsequent main crop

Simulating Root Density Dynamics and Nitrogen Uptake – Can a Simple Approach be Sufficient?

The modeling of root growth in many plant–soil models is simple and with few possibilities to adapt simulated root proliferation and depth distribution to that actually found with different crop species. Here we propose a root model, developed to describe root growth, root density and nitrogen uptake. The model focuses on annual crops, and attempts to model root growth of different crop species and row crops and its significance for nitrogen uptake from different parts of the soil volume

Simulating Root Density Dynamics and Nitrogen Uptake -Field Trials and Root Model Approach in Denmark

Plant soil and atmosphere models are commonly used to predict crop yield and associated environmental consequences. Such models often include complex modelling of water movement, soil organic matter turnover and above ground plant growth. However, the root modelling in these models is often very simple, partly due to a limited access to experimental data. Here we propose a root model developed to describe root growth, root density and nitrogen uptake. The model focuses on annual crops, and attempts to model root growth of different crop species and row crops and its significance for nitrogen uptake from different parts of the soil volume

Simulating Soil Organic Matter Transformations with the New Implementation of the Daisy Model

Daisy is a well-tested deterministic, dynamic soil-plant-atmosphere model, capable of simulating water balance, nitrogen balance and losses, development in soil organic matter and crop growth and production in crop rotations under alternate management strategies. Originally it was developed as a system of single models describing each process involved, but recently it has been developed into a framework, which can be used for implementation of several different models of each of the different processes. Thus, for example a number of different models for simulating soil water dynamics can be chosen depending on the purpose of the simulation and the availability of data for parameterisation. The sub-model simulating soil organic matter is still a fixed component in the Daisy terminology. This means that there is currently only one model, which can be used to simulate soil organic matter transformations. However this sub-model can be changed considerably. Some examples are given

Catch Crops in Organic Farming Systems without Livestock Husbandry - Simulations with the DAISY model

This paper presents simulations of the soil-plant-atmosphere model DAISY based on an organic crop rotation with incorporation of different catch crops following pea as a leguminous cash crop. Special emphasise was put on the simulation of N-mineralisation/-immobilisation and of soil microbial biomass N. The DAISY model was able to simulate soil mineral N and soil microbial biomass N after soil incorporation of catch crop plant residues to some extend. Several processes need further attention and may be integrated into the DAISY model: (1) soil tillage induced mobilisation of organic material including considerable amounts of organic N, (2) winter killing of sensitive plant species and varieties, (3) decomposition of plant residues at the soil surface as occurring after winter killing, (4) decomposition of easily decomposable plant residues at low temperatures, (5) soil microbial residues as an organic pool temporarily protected against turnover. Furthermore, reliable criteria for the subdivision of green plant residues into an easily decomposable pool and a more recalcitrant pool have to be developed