Dry matter accumulation and NPK nutrient uptake and transfer of seed lotus (Nelumbo nucifera Gaertn.) throughout the harvesting period

Objectives The characteristics of dry matter accumulation, nitrogen (N), phosphorus (P) and potassium (K) uptake and transfer in seed lotus were studied, and providing a theoretical basis for scientific fertilization of seed lotus.

Methods A micro-plot experiment (3 m²) was conducted in Guangchang, Jiangxi Province, taking two cultivars of Taikonglian 36 and Jianxuan 17 as the tested materials. Plant samples were collected at 85 days (beginning harvesting), 103 days (early harvesting), 121 days (peak harvesting), 139 days (middle harvesting), 160 days (late harvesting), and 180 days (ending harvesting) after transplanting, respectively. The dry matter weight, N, P and K content of different organs (parts) were determined, and the periodical accumulation and transfer of dry matter and NPK were calculated.

Results The dry matter of seed lotus was mainly accumulated from the beginning to peak harvesting period (85−121 days after transplanting), and the dry matter accumulation in source organs (leaves, rhizomes, etc.) first increased and then decreased, reaching peaks at the end of flowering. During the period, fruit setting period (139 days after transplanting, middle harvesting). The dry matter accumulation in the receptacle and fruit kept increasing, especially after the developed rhizomes starting. The N, P and K content in source organs maintained at a high level before 139 days and then decreased rapidly or gradually, depending on the cultivars or the organs, while the NPK content in flower bud, fruit and developed rhizome were relatively stable during the whole harvesting period. The dynamics of N and P content in receptacle was similar to those in leaves, and the dynamics of K content in receptacle was similar to those in fruits. N and K mainly accumulated during 85−121 days after transplanting, and P mainly accumulated during 85−139 days, accounting for 53.9%, 61.4% and 55.9% of the total N, P and K accumulation, respectively. During 139−180 days after transplanting, the N accumulation increment was distributed to receptacle, fruit and developed rhizome by 3.0%, 67.8% and 29.2%, respectively, the P and K accumulation increment were distributed to the above three organs by 1.5%, 65.0%, 33.5%, and by 6.7%, 40.5%, 52.8%, respectively. The exportation of N, P and K from the source to sink organs accounted for 88.8%, 49.9% and 77.7% of the total periodical accumulation from 139 to 180 days. The accumulation of N, P₂O₅, and K₂O for producing 100 kg cotyledon were 7.50 kg, 3.47 kg and 9.45 kg on average, with the N∶P₂O₅∶K₂O ratio of 1∶0.46∶1.26.

Conclusions From the end of flowering and fruit setting period to the end of harvesting, the accumulation of N, P and K in seed lotus can be divided into two sinks, “receptacle + fruit” (reproductive organs) and “developed rhizome” (vegetative organ), with fruit development being the dominant sink. The N and K accumulation in sink organs is mainly transferred from the source organs, while P accumulation is half transferred and from absorption. Therefore, sufficient nutrient supply in flowering and fruit setting period and continuous P supply in rhizome developing period is very important for high yield of both lotus fruit and developed rhizome.