Manganese (Mn) deficiency in wheat is a typical nutritional problem on calcareous soils, especially under rice-wheat rotation system. However, wheat yield loss induced by Mn deficiency may be reduced through interactions between two crops with different Mn utilization potentials. In 2003, a pot experiment was conducted at a greenhouse of China Agricultural University to evaluate the effects of oat/wheat intercropping on growth and Mn nutrition of wheat grown in a Mn-deficient soil. The pot experiment included two factors: root-isolation (including solid barrier, mesh barrier and no barrier) and intercropping combination. Two wheat cultivars (Chuanmai28 and 9023) and three oat cultivars (Bayou 1, Bayou 3 and Jizhangyou 4) were used in this experiment. Each of the 18 treatments (3×2×3) was replicated three times. All treatments received the same rates of Ca(NO_３)₂ (0.3 g N kg^－1), Ca(H_２ＰＯ_４)2 (0.2 g P₂O₅ kg^-1) and K₂SO_４ (0.3 g K₂O kg^-1) as NPK fertilizers before planting. The ratios of N∶P2O5∶K2O were 1.5∶1∶1.5. All plants were harvested after 2 months of growth. Shoot dry weight and Mn concentration were measured and shoot Mn uptake was calculated by multiplying biomass by Mn concentration. The original soil was an alluvial paddy soil with pH 7.69, O.M. 34.9 g•kg^－１, exchangeable Mn 1.0 mg•kg^－１, and active Mn 19.0 mg•kg^－１.
Wheat Mn-deficient symptoms were initially observed at the fourth-extended leaf stage of wheat, and the most serious symptoms of Mn deficiency appeared at the sixth-extended leaf stage. But the symptoms gradually diminished as air temperature increased, providing evidence that low temperature is a primary cause for wheat Mn-deficiency. The symptoms of Chuanmai 28 were more serious than those of 9023 and no Mn-deficient symptoms of oat were observed, suggesting that Chuanmai 28 was more sensitive to Mn deficiency than 9023 and both of these two wheat cultivars were more sensitive to Mn deficiency than three oat cultivars.
Compared with the solid barrier and mesh barrier treatments, complete root interaction (no barrier treatment) led to significantly higher shoot dry weight and Mn uptake of the two wheat cultivars. The shoot Mn concentrations of the two wheat cultivars, however, were higher in the solid barrier treatment than in the other two treatments (mesh barrier and no barrier). The DTPA-Mn in soil grown oat was higher than grown wheat across barrier treatments and Mn concentration and Mn uptake of oat genotypes were much higher than those of wheat genotypes. Consequently, we speculate that oat may facilitate the growth and improve the manganese nutrition of wheat under intercropping by activating the insoluble soil Mn oxides with root secretion. Observed increased growth and higher Mn uptake of wheat intercropped with oat (no barrier) provide initial support for this hypothesis.