Ammonium fertilization increases pearl millet yield by promoting early root growth, higher tillering, and water use during grain filling in a low P Sahelian soil

Abstract

Background: Adaptation of pearl millet [Pennisetum glaucum (L.) R. Br.] to low soil phosphorus (P) at early seedling stages and efficient P fertilizer application are crucial for its survival in the West African Sahel. While addition of (Formula presented.) to P in the microdose technique has been reported to stimulate early growth of pearl millet, there is little information regarding root length (RL) at different timings. Aims: Our study aimed at assessing the effects of added (Formula presented.) and (Formula presented.) to P on (1) pearl millet agronomic traits such as root and shoot growth and (2) the water use dynamics during the cropping cycle. Methods: Twenty-four “RhizoTubes” filled with P-deficient soil were used to grow pearl millet under three treatments: (T1) placed P addition alone at 0.4 g per seed hole, Pplaced, (T2) Pplaced + (Formula presented.), and (T3) Pplaced + (Formula presented.). At 2, 3, 4, and 5 weeks after sowing (WAS) we took non-destructive measurements of RL. Water use (transpiration) was measured from 3.5 to 9 WAS. Results: At early growth, roots in the topsoil of T2 were longer than T3 and T1 roots (at 4 WAS: 129.3 cm for T2, 87.5 cm for T3, and 93.3 cm for T1, p < 0.05). Total RL at 2 WAS correlated positively with seedling height and final grain yield. Fertilization with (Formula presented.) reduced the time to flowering and increased the number of tillers and grain yield, whereas addition of (Formula presented.) increased vegetative dry matter at harvest and water use efficiency. Conclusions: Our findings suggest that fertilization with (Formula presented.) plays a critical root stimulating role at early growth stages, seemingly by increasing lateral root initiation, which carries through to a larger water use during grain filling and higher grain yield.