Inter‐rotational Effects of Fertilization and Weed Control on Juvenile Loblolly Pine Productivity and Nutrient Dynamics

Abstract

The inter‐rotational effects of fertilization and weed control treatments on the productivity and soil nutrient availability of loblolly pine (Pinus taeda L.) stands growing on a North Florida Spodosol were investigated using two replicated, randomized complete block design experiments. The first rotation treatments were: control (C), fertilizer only (F), weed control only (W), and fertilizer + weed control (FW). One experiment was actively retreated as in the previous rotation, while the second was left untreated (CC, CF, CW, and CFW). A common full‐sib loblolly pine family was planted in both experiments. After three growing seasons, the second‐rotation pine growth consistently outperformed the first rotation. The actively retreated FW treatment had fourfold higher aboveground pine biomass than the C treatment (7.7 Mg ha−1); the untreated CF (17.9 Mg ha−1) treatment had 1.5‐fold higher pine biomass than the CFW treatment. While a suite of improved cultural practices (e.g., advanced genetics and site preparation) and environmental factors may be responsible for higher growth responses in the second rotation than the first in both experiments, lower growth response in the CFW treatment compared with the CF treatment was associated with lower soil P availability (r = 0.8, p < 0.01) and historical P movement from the E to Bh and Bt horizons. These results suggest that the understory vegetation and forest floor from the first rotation served as an important nutrient sink, especially for P, which then subsequently became a nutrient source (through mineralization) in the second rotation. Historical P fertilization on flatwoods Spodosols may thus alleviate the need for P fertilization during stand establishment when an intact understory was present in the previous stand.