Controlling canopy formation, flowering, and yield in field-grown stands of peanut (Arachis hypogaea L.) with ambient and regulated soil temperature

The effects of soil temperature on canopy formation, flowering, and yield of peanut stands remain to be elucidated, although considerable effort has been expended on studying the morphology, phenology, ecology and physiology of peanut. We conducted field experiments in 2000 and 2001 to investigate the dynamics of canopy formation in terms of the production of branches and leaves, flowering frequency, and yield in field-grown stands of peanut (Arachis hypogaea L.). The experiment had three soil temperature treatments-ambiet, cool, and warm. Their mean values, from sowing until differences in soil temperatures between treatments disappeared, were about 24, 22 and 27 °C, respectively. The numbers of primary branches (B(P)), total branches (TB(r)), main stem leaves (L(f)), and total leaves (TL(V)) were significantly higher in stands grown in warm soil and lower in stands grown in cool soil. The values of ambient stands ranked in between. The ratio of the number of primary branches to the total number of branches (BP:TB(r)) and the ratio of the number of main stem leaves to the total number of leaves (L(f:)TL(V)) decreased with increasing soil temperature. L(f) was an important indicator of the formation of canopy as a function of TL(V)(TL(V)=0.19L(f)(2.43), R(2)=0.96), L(f:)TL(V)(Lf:TL(V)=5.4L(f)(−1.42), R(2)=0.90), TB(r) (TB(r)=-5.0+1.6L(f), R(2)=0.87), and B(P):TB(r) (B(P):TB(r)=3.4L(f)(−0.86), R(2)=0.81). The minimum value of L(f) for the initiation of branching was 3. The rate of leaf production (-°C days) was maximum in warm soil and minimum in cool soil. A similar trend was found for the rate of branch production (-°C days), but treatment differences were not significant. A close linear correlation (r=0.89, P<0.02) was found between the rates of production of branches and leaves. The plastochron interval (PI, the number of degree days between the appearance of two successive leaves on the main stem) increased as the soil temperature decreased. Stands in the warmer and cooler temperature treatments produced more and fewer flowers, respectively, than those in the ambient temperature treatment. Stands grown in ambient soil produced the greatest proportion of immature pods, those in cool soil produced the most juvenile pods, and those in warm soil produced the most mature pods. This resulted in the greatest individual pod and kernel weights, pod yield, and shelling out-turn in warm soil and the least in cool soil. Our results show that warmer soil can produce an early, well-organized canopy with a higher pod yield, individual seed weight, and shelling out-turn than normal in cool-temperate regions, where temperature often falls below the optimum for peanut cultivation.