Effect of different nutrient combinations on root growth and nutrient accumulation in sorghum

Sorghum, one of the important grains in the world, can grow well in low fertility soils. In order to understand the response of nutrient accumulation and root growth in sorghum to N, P and K stresses, a long-term experiment consisting of 5 treatments (NPK, PK, NK, NP and CK) under conditions of sorghum/maize rotation system was initiated in 2011. The indi-vidual treatments of the experiment ensured differences in availability of soil N, P and K before sowing sorghum in 2016. The results showed that compared with NPK treatment, PK treatment increased total root length by 18.29% and decreased total root volume by 26.53%. Also under PK treatment, sorghum root distribution was mainly in the 0-10 cm soil layer. The proportion of fine roots with diameter less than 0.5 mm increased significantly under PK treatment. Compared with NPK, total length, total surface area and total root volume of sorghum decreased respectively by 24.03%, 27.48% and 41.29% under NK treatment. Without K (i.e. under NP treatment), the growth of fine roots was inhibited. Removal of either N or P or K decreased the accumulation of the corresponding element in sorghum. It was recommended not to induce N or limit N and K translocation from vegetative organs to grains. Both the combinations NK and NP inhibited the transfers of N, P and K to grain from vegetative parts. The accumulation and translation of N, P and K were regulated by root morphology. There were significant relationships between both N and K accumulation and individual root parameter (total root length, total root surface area and total root volume). Compared with P and K accumulation, N accumulation in sorghum had an obviously correlation with both N translocation from vegetative organs to grains and aboveground biomass. In summary, the response of root morphology and nutrient accumulation in sorghum to individual N, P or K stress was different. The results were useful for the cultivation of sorghum in marginal soils.