Studies were made to investigate the suitability of cereal species and varieties for use in a direct drilling system and to establish whether there is scope for selecting or breeding barley varieties adapted to compact soil conditions.
Initially field experiments were made to study the ability of contrasting cereal varieties to grow in compact soil (direct drilling)by comparison with their growth and productivity in normally ploughed and cultivated soil. The relative grain yields after direct drilling and ploughing varied between sites and seasons. In some experiments there was evidence of a variety x cultivation interaction] however it was concluded that the results were too inconsistent to identify factors which made a variety adapted to compact soil.
It was concluded, from the literature, that increased soil compaction was one of the main factors limiting crop growth after direct drilling. Studies were made to establish whether there is scope for selecting or breeding barley varieties with root systems adapted to compact soil conditions. The first step was to establish the range of variation in root system characters among barley varieties. To facilitate the study of varieties with a wide range of phenotypes all subsequent studies were made in the laboratory or glasshouse.
A survey was made of the seedling root characters of 96 barley varieties, which had been selected to have as diverse a geographical and/or genetic origin as possible. Measurements of seminal root number, length and diameter among varieties indicated that expression of these characters were mainly controlled by additive polygenic systems. An estimate of the broad sense heritability of root characters was made from a study of 10 selected varieties. This and other evidence indicated that seedling root number was the most strongly inherited root character, followed in decreasing order by total root length, mean seminal root length and root diameter.
In 1978 experiments were made in which barley varieties were grown in soil artificially compacted to varying bulk densities.Varieties with diverse seminal root numbers and diameters were selected for these experiments from the varieties previously surveyed.
In general seedling root length decreased and root diameter increased with increasing soil compaction. Varietal differences in seminal number and diameter did not affect their response to soil compaction.Certain varieties had more vigorous root systems than others and consistently produced relatively greater root lengths. It was suggested that such varieties would be better able to meet the plant requirements for nutrients in compact soil. The artificially compacted soil used in these experiments lacked the cracks and continuous pores characteristic of many field soils compacted under direct drilling. It was argued that in a compacted field soil a variety with many seminal roots would have a greater chance of one or more roots encountering the cracks along which roots can grow and proliferate sufficiently to meet the needs of the developing plant.