Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2018
Publication Date: N/A
Interpretive Summary: Of the many nutrients in pelletized poultry litter (PPL), nitrogen (N) is probably the most important to cotton (Gossypium hirsutum L.) production. Because N stress limits several growth processes, properly managing N fertility is an important step in optimizing lint yield and nitrogen use efficiency (kg biomass or lint per kg applied N). Soil nitrate is the principle source of N for growth. A substantial portion (50-60%) of the N in pelletized poultry litter is in organic form which releases nitrate slowly in the soil solution following mineralization during each growing season and any remaining organic N can persist in soil and affect crop productivity in subsequent years. Scientists conducted field studies to determine the residual (carry-over) effects of 6.7 Mg ha-1 PPL (220 kg ha-1 N) applied as a sub-surface band in the 2010-2013 growing seasons on soil nitrate levels, leaf area index (LAI, leaf area per unit of ground area) and N removal by cotton in 2014-2016. Fertility treatments consisted of residual PPL, residual PPL with 84 kg ha-1 N (as urea-ammonium nitrate) at squaring stage, N fertilization with 140 kg ha-1 N, and no N fertilization (control). Results for the 140 kg ha-1 fertilizer N and residual PPL with 84 kg ha-1 N treatments clearly indicated continued development of green leaf area is proportional to growth, N removal, and lint yield. Applying 84 kg ha-1 N at squaring stage to residual PPL plots significantly boosted LAI during boll-filling stage in early August (73-92 days after sowing) and resulted in LAI > 3, large enough to cause canopy closure. This practice improved recovery of the residual organic N and applied N, reducing soil NO3-N levels in top 30 cm after harvest by approximately 61%. Based on similar growth characteristics of cotton receiving residual PPL with 84 kg ha-1 N and 140 kg ha-1 fertilizer N, approximately 56 kg ha-1 N was available to plants in the 2 years following the cessation of PPL application. Results indicated the residual organic N in pelletized poultry litter can have long-lasting, agronomic and environmental benefits in cotton production systems.
Technical Abstract: In a previous study that compared pelletized poultry litter (PPL) and inorganic N applied in subsurface bands at nearly equivalent N rate to cotton (Gossypium hirsutum L.), PPL enhanced lint yield and soil fertility. The study reported here-in presents the residual (carry-over) effects of PPL applied in 2010-2013 on cotton leaf area, N use efficiency (NUE), and yield. Four treatments were replicated four times and each strip-plot experimental unit was 28 m long with six, 0.97-m wide rows. Treatments in 2014 and 2015 were (i) no N (control), (ii) residual PPL only, (iii) residual PPL with 84 kg ha-1 N (as urea-ammonium nitrate, UAN) at squaring stage, and (iv) 56 and 84 kg ha-1 N at planting and squaring, respectively. Treatments in 2016 were (i) control, (ii) residual PPL with 56 kg ha-1 N at squaring, (iii) residual PPL with 56 kg ha-1 N at planting and squaring, and (iv) split application of 112 kg ha-1 N. Applying 84 kg ha-1 N to residual PPL plots significantly (P < 0.05) boosted leaf area index during the boll-filling period. Averaged across years, N removal did not differ between residual PPL with 84 kg N ha-1 and fertilizer N treatments (112 vs. 116 kg N ha-1), but was considerably less with residual organic N only (40 kg N ha-1). Lint yield was greater (P < 0.01) in PPL with fertilizer N than fertilizer N only by approximately 10% in 2014 (1795 vs. 1633 kg ha-1), 5% in 2015 (1898 vs. 1809 kg ha-1), and 20% in 2016 (1860 vs. 1554 kg ha-1), suggesting residual PPL enhanced NUE. Following the cessation of PPL applied in sub-surface bands, nutrient management should account for N availability due to carryover of organic N sources.