International Journal of Plant & Soil Science

Aims: Growth chamber experiments were performed in order to determine the influence that biochars originating from two separate sources (mixed-hardwoods and poultry litter) have on the growth and development of cotton (Gossypium hirsutum L.) seedlings used alone or in combination with conventional fertilizers.
Study Design: The treatments consisted of a 3 by 3 full-factorial arrangement of biochar and fertilizer rates organized in a complete randomized design.
Place and Duration of Study: The trials were conducted in the fall of 2010 and 2012 at the Altheimer Laboratory located at the University of Arkansas Research and Extension Station, Fayetteville, Arkansas (USA).
Methodology: In both experiments, 54 1.5 liter pots were each filled with 1.8 kilograms of a Captina silt loam soil (Typic fragiudult). Both biochar types were added to pots at three equivalent rates: (1) no biochar (control); (2) 5,000 kg/ha; and (3) 10,000 kg/ha while fertilizer was also added to pots at three equivalent rates: (1) no fertilizer (control); (2) 31-23-49 kg/ha (N-P-K); and (3) 62-46-98 kg/ha (N-P-K). The plants were grown for eight weeks and then harvested. Data collected at harvest included plant height, chlorophyll content, leaf area, number of main-stem nodes and number of fruits along with plant dry matter.
Results: Both biochar types contributed to increases in numerous plant developmental characteristics. Statistical analysis showed that the hardwood chip based biochar had a more pronounced influence on most plant developmental measurements compared to the poultry litter based biochar. The main effect of biochar in 2010 demonstrated significant increases regarding response variables such as leaf area; control (654.41 cm²), highest rate of biochar (748.63 cm²) (P < .0001), stem dry matter; control (5.08 g), highest rate of biochar (6.08 g) (P < .0001) and fruit dry matter; control (0.20 g), highest rate of biochar (0.52 g) (P < .0001). The main effect of biochar in 2010 also significantly decreased chlorophyll content; control (53.80 SPAD units), highest rate of biochar (50.03 SPAD units) (P < .0001) and average node length; control (4.08 cm), highest rate of biochar (3.89 cm) (P = .001). The main effect of biochar in 2012 resulted in significant increases in the response variables of stem dry matter; control (2.87 g), highest rate of biochar (3.25 g) (P = .040), leaf dry matter; control (3.66 g), highest rate of biochar (4.21 g) (P = .010) and total plant dry matter; control (6.71 g), highest rate of biochar (7.55 g) (P = .032). Statistical analysis showed that the main effect of biochar in 2010 slightly surpassed the effects of the fertilizer main effect while generating more significant responses than the interaction of biochar and fertilizer. Further statistical analysis demonstrated that the main effect of fertilizer in 2012 exceeded the biochar main effect and an interaction between biochar and fertilizer was not observed.
Conclusion: Analyses of individual biochar rates for both experiments, along with the interaction of biochar and fertilizer treatments in 2010, demonstrated that the mixed-hardwoods based biochar had a more positive effect on cotton plant development than the poultry litter based biochar. Additional research is needed concerning the nature and ability of biochars of different origins to slowly release plant available nutrients over time that can contribute to cotton production.