Proficiency of green fallow compared to bare fallow, grain legume and cereal pre-crops in a long-term crop rotation

Long-term experiments (LTEs) are an important tool to investigate the effects of crop rotation and fertilization measures under climate change conditions. However, LTEs that integrate fallow management strategies, including green and bare fallow are hardly available in Europe today. The objective of our study is to explore how the integration of green and bare fallow, grain legume and cereal crops in long-term experiments enhances ecosystem resilience under changing climate conditions, to better understand their contributions to sustainable agricultural practices. Therefore, a LTE established in 1982 aimed to study the role of fallow lands (green vs. bare), grain legume and cereal pre-crops on the yields of subsequent cereal crops. The study was conducted within a rotational cropping system and evaluated after at least 10 full crop rotations from 1982 to 2019. The experiment included five different pre-crops (green fallow, bare fallow, field bean, oat, and maize) followed by three years of cereal cultivation (winter wheat, winter rye, spring barley) in combination with four levels of mineral fertilization (unfertilized; PK 50 %; PK 100 % + N 50 %; PK 100 % + N 100 %). The field trial was conducted as a full factorial split plot design, with spatially randomized field repetitions in four blocks. It was found that within the ten crop rotations from 1983 to 2019, the mean relative yields of wheat as the first subsequent crop were significantly higher after green fallow (139 %) than grain legume (field bean)/bare fallow (120 %), maize (100 %) and oat (94 %). A rotational system of green fallow not only enhanced the yield effects of the 1st subsequent crop (winter wheat), but also extended the benefits to the 2nd (winter rye) and 3rd (spring barley) subsequent crops. Further on, green fallow had a synergistic effect of PK 100 % + N 100 % on grain yield of winter wheat when compared to bare fallow, field bean, oat and maize. Green fallow and continuous soil cover with crop residue mulch with mineral fertilizer application improved N cycling and crop productivity by increasing soil N availability in the agroecosystem. A short period of bare fallow led to increase net N mineralization of organic matter compared with cropped lands and increases yield in immediately following crop when water availability is sufficient. • Climate-smart rotations with clover or vetch green fallows enhance crop yield. • Pure cereal rotations need high N and cut yield due to pests and soil-borne diseases. • Bare fallow can raise yield by improving aeration and N mineralization. • Including bare fallow lowers C input and reduces yield in crop rotations.