Crop yield, root growth, and nutrient dynamics in a conventional and three organic cropping systems with different levels of external inputs and N re-cycling through fertility building crops

Summary

One core idea behind organic production is that cropping systems should be less dependent on resource import than conventional production and minimize negative environmental effects. This study aimed to test novel organic rotations, designed to reduce reliance on external resource import. We compared a conventional system (C) and an organic system relying on manure import (O1) to two rotations (O2 and O3), both relying on autumn cover crops for soil fertility, and in O3 green manure rows were left as intercrops. Resource import differed between 149, 85, 25 and 25 kg N ha-1 year-1 in C, O1, O2 and O3.
Crop yields were lower in the organic systems (on average 82% of conventional yields), differing among crops, when based on the area grown with main crops. In O3, some of the vegetable field area was allocated to intercrops, so vegetable yields ha-1 were only 63% of conventional yields. Differences in crop quality parameters, e.g. damages by pests/diseases were few and not systematic. Clear effects on nutrient balances and nitrogen leaching indicators were found but only few effects on root growth were observed. However, green manures almost doubled the soil exploration (0-2.4 m) by active roots from 21% (C) to 38% (O2). Average subsoil (1-2 m) inorganic N content was 74 and 61 kg N ha-1 in C and O1 vs. only 22 and 21 kg N ha-1 in O2 and O3, indicating strongly reduced N leaching loss in O2 and O3. In short, the main distinctions were observed between systems based mainly on nutrient import (C, O1) vs. systems based mainly on green manure (O2, O3), rather than between conventional and organic systems.