Objectives Root morphology affects crop tolerance to drought. We attempted to improve the root growth in deep soil through a suitable application depth of phosphorous fertilizer, in order to provide an effective nutrient management way for the growth of tartary buckwheat.
Methods Using 'Heifeng1' buckwheat (Fagopyrum tataricum L.) as the test material, an experiment was carried out using root canal soil column cultivation method. Three soil moisture treatments were setup as the field water capacity of 65%–75% (W1), 45%–55% (W2) and 35%–45% (W3), under each water treatment, phosphorous fertilizer were placed at 10 cm (P10), 20 cm (P20), 30 cm (P30) deep and at all the three depth (P-all). Buckwheat seedlings with three-leaves-one-sprout were cultivated for 22 days before sampling. The biomass of shoot and root were weighted, and the growth and root distribution of buckwheat were measured.
Results Drought stress inhibited the growth, dry biomass accumulation and root development of tartary buckwheat plants. Among them, W3 inhibited the most. Compared with W1, the plant height, stem diameter and leaf area of tartary buckwheat in W3 were decreased by 17.20%, 18.03% and 23.17%, respectively. The root length, root surface area and root volume were decreased by 16.97%, 20.39% and 17.39%, respectively. The dry mass of above-ground and root decreased by 39.16% and 28.60%, respectively. Drought stress promoted root infiltration and increased root distribution in deep soil. Compared with W1, the average root length of 0–10 and 10–20 cm soil layers under W2 and W3 were decreased by 30.18% and 27.55%, 41.83% and 41.02%, and the root dry mass decreased by 36.62% and 33.61%, 49.72% and 48.11%, respectively, while the average root length of tartary buckwheat in 20–30 cm and 30–45 cm soil layers were increased by 33.53% and 42.52%, 31.74% and 50.95%, and the root dry mass were increased by 13.70% and 26.84%, 5.85% and 28.64%, respectively. P application could increase the root growth in the layer of P placement. Compared with the P-all treatment, the root length in 10–20 cm soil layer under the P10 treatment, that at 20–30 cm soil layer under P20 treatment and that at 30–45 cm soil layer under P30 treatment were increased by 18.96%, 32.39% and 28.73%, respectively, the root dry mass of the three placement depths were increased by 26.62%, 30.74% and 24.65%, respectively. Under all the three water conditions, the dry root mass in both 0–10 cm and 10–20 cm soil layers of P10 were significantly higher than those of the other P treatments, and the difference of dry root mass among the other P treatments was significant as well.
Conclusions Under drought stress, the placement depth of phosphorous significantly affects the distribution of tartary buckwheat roots in soil, suitable application depth could stimulate the roots access to deeper soil layers, which provides the roots with larger room to absorb soil nutrients and water, and ultimately promoting the growth of tartary buckwheat. Under the experimental conditions, applying P at 10 cm depth is recommended.
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