Reduced row spacing improved yield by optimizing root distribution in maize

Roots play major roles in plant anchorage, water and nutrient uptake, crop growth and yield. Knowledge regarding yield responses to root spatial distribution is still limited in maize. Here we designed three plant densities in the tube and in the field, respectively. The tube study included plant densities of 1, 2, and 3 plants tube–1 and field study included 50025 (D50025), 67500 (D67500), and 100050 (D100050) plants ha–1, with two row spacings in D50025 (60 and 80 cm), three row spacings in D67500 (40, 60, and 80 cm), and two row spacings in D100050 (40 and 60 cm). With increased plant density and decreased row spacing grain yield improved, but root size and root biomass per plant decreased. Root dry weight per plant increased by 25–32 % at D50025 and decreased by 29–38 % at D100050 compared to D67500. Horizontally, reducing row spacing increased inner roots and reduced outer roots. There were significant correlations of yield with inner (R2 = 0.603** for D67500) and outer (R2 = −0.544* for D67500) root dry matter. Vertically, reducing row spacing increased root dry weight and most of the roots were distributed in the top 0–10 cm soil layer. Overall, high plant density inhibited root growth, but narrow row spacing compensated this inhibition to some extent by optimizing root distribution, thus increasing grain yield. Horizontal root distribution had a greater effect on grain yield than vertical distribution under high density condition, which alleviated inter-plant root competition and increased yield.