Objectives The effect of calcium application rate on the distribution of photosynthetic carbon in peanut plant across pod development stage was studied, to understand the mechanism of calcium fertilizer in peanut growth and yield formation.

Methods A peanut cultivar ‘Xianghua 55’ was used as the test materials to carry out a pot experiment. The treatments were basal applying CaO 0, 75, 150, and 300 kg/hm², denoted as Ca0, Ca75, Ca150 and Ca300, respectively. At the young fruit, pod bulking, pod setting, and kernel filling stage, ¹³C-CO₂ (300–350 mg/kg) were prepared through reaction of ¹³C-Na₂CO₃ and H₂SO₄ solution (1 mol/L) inside the growth chamber, to label the photosynthetic carbon in plants, respectively. At harvest, plant was divided into different organs for the determination of ¹³C abundance, dry matter accumulation (DMA), and the kennel yields.

Results Ca application had significant effects on DMA of peanut plants. Ca75 treatment increased more DMA in roots and stems, and Ca150 increased more DMA in leaves, pegs, kernels, shells, and whole plant which were 12.43%, 33.60%, 34.35%, 11.91% and 14.82% higher than Ca0 did (P<0.05). Ca application significantly increased the peanut pod yield, kernel rate and the full fruit rate, did not affect the double kernel fruit rate. Ca150 was recorded the highest pod yield, which was 10.5% higher than that of Ca0. The δ¹³C abundance in kernel was highest at kernel filling stage under Ca0, Ca75 and Ca300 treatments, and was the highest at pod bulking stage under Ca150 treatment. With the extension of pod stage, the accumulation of ¹³C in peanut plant increased first and then decreased, with the peak accumulation at pod bulking stage. The total accumulation of ¹³C in peanut plant in Ca150 treatment was significantly higher than that in other treatments. With development of the peanut pod, the distribution rate of ¹³C in peanut kernel kept increasing until as high as 41.0% (Ca0)–48.3% (Ca75) at kennel filling period. The higher the CaO rate, the higher the distribution rate of ¹³C in kernel. The CaO rate 75–150 kg/hm² was conducive to transfer ¹³C from root and needle to kernel, while the CaO rate 150–300 kg/hm² was conducive to transport ¹³C from leaves and shells to kernels.

Conclusions In Ca deficient soil, appropriate calcium application rate could promote the accumulation of ¹³C in peanut plants, significantly increase the distribution ratio of photosynthetic ¹³C in peanut kernel, laying a foundation for the increase of yield. Under the test conditions, CaO 150 kg/hm² was recommended as the appropriate amount of calcium fertilizer to obtain the highest production benefit.