Root morphology and nutrient efficiency of Tibetan barley and peas in response to planting patterns and fertilization levels

Objectives We examined the root morphology and nutrient utilization of Tibetan barley (Hordeum vulgare var. coeleste Linnaeus) and peas (Pisum sativum L.) in mixed cropping systems under different fertilization levels.

Methods The study used pot and field experimental methods at the Qinghai University experimental base. The cropping patterns included single cropping of Tibetan barley and peas and mixed cropping of both crops. Fertilization levels were no fertilization (N₀P₀), low nitrogen and phosphorus rate (N₁P₁), and high nitrogen and phosphorus rate (N₂P₂). The root morphology, biomass, N and P uptakes of Tibetan barley and peas were analyzed, and nitrogen and phosphorus competition ratio between the two crops was calculated.

Results Compared with single cropping, mixed cropping (P<0.05) increased the shoot and root dry weight of Tibetan barley by 32.1% and 15.3%, decreased the root-to-shoot ratio by 13.1%, increased the total root length, root surface area, total root volume and root tip number by 21.7%, 43.7%, 79.6%, and 44.8%, increased root N uptake and total N uptake by 75.8% and 72.7% and root P uptake and total P uptake by 56.3% and 60.0%. On the contrary, mixed cropping (P<0.05) decreased peas shoot and root dry weight and the root-to-shoot ratio by 19.3%, 27.9%, and 9.7%, decreased the shoot and root N uptake and total N uptake by 24.7%, 32.5%, and 28.0%, respectively. Compared with single cropping, the shoot N accumulation in Tibetan barley under mixed cropping (P<0.05) increased by 9.8%, 34.6%, and 39.6%, and shoot P accumulation increased by 11.6%, 18.7%, and 16.5% at tillering, jointing, and maturity stages. Peas shoot N accumulation under the mixed cropping system decreased by 13.8%, 18.0%, and 17.5%; the shoot P accumulation decreased by 26.1%, 15.8%, and 19.9% at branching, flowering and podding stages. The results of multiple linear regression analysis showed that the root surface area and average root diameter had significant correlation with the N absorption, and the root volume had significant correlation with the P absorption of Tibetan barley and pea. Among the three fertlizer levels under mixed cropping, N₁P₁ was recorded the largestroot length and surface area of Tibetan barley, but the lowest root development of peas.

Conclusions The N and P uptake of Tibetan barley and peas was positively correlated with the root surface area. Inefficient N and P supply increased the root morphology indexes of Tibetan barley but decreased peas’ root surface area and volume under mixed cropping system. Tibetan barley is the “beneficiary” while Pea is the “contributor”. Under the low fertilizer level, the mixed cropping system enhanced nitrogen and phosphorus nutrient ultilization rate and land equivalent ratio. Under sufficient fertilization, the mixed cropping system did not influence the two crops’ root morphology, with less benefit from the system.