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Deteriorating soil fertility and the concomitant decline in agricultural productivity are major concerns in many parts of the world. A pot experiment was conducted with a Ferralsol to test the hypothesis that application of biochar improves soil fertility, fertiliser-use efficiency, plant growth and productivity, particularly when combined with compost. Treatments comprised: untreated control; mineral fertiliser at rates of 280 mg nitrogen, 70 mg phosphorus and 180 mg potassium pot–1 (F); 75% F + 40 g compost pot–1 (F + Com); 100% F + 20 g willow biochar pot–1 (F + WB); 75% F + 10 g willow biochar + 20 g compost pot–1 (F + WB + Com); 100% F + 20 g acacia biochar pot–1 (F + AB); and 75% F + 10 g acacia biochar + 20 g compost pot–1 (F + AB + Com). Application of compost with fertiliser significantly increased plant growth, soil nutrient status and plant nutrient content, with shoot biomass (as a ratio of control value) decreasing in the order F + Com (4.0) > F + WB + Com (3.6) > F + WB (3.3) > F + AB + Com (3.1) > F + AB (3.1) > F (2.9) > control (1.0). Maize shoot biomass was positively significantly correlated with chlorophyll content, root biomass, plant height, and specific leaf weight (r = 0.99, 0.98, 0.96 and 0.92, respectively). Shoot and root biomass had significant correlations with soil water content, plant nutrient concentration, and soil nutrient content after harvesting. Principal component analysis (PCA) showed that the first component provided a reasonable summary of the data, accounting for ~84% of the total variance. As the plants grew, compost and biochar additions significantly reduced leaching of nutrients. In summary, separate or combined application of compost and biochar together with fertiliser increased soil fertility and plant growth. Application of compost and biochar improved the retention of water and nutrients by the soil and thereby uptake of water and nutrients by the plants; however, little or no synergistic effect was observed.

In small catchments with rapid flood pulses, detailed temporal data are essential because high-discharge events can be measured in hours and days, rather than weeks and months. Using high-resolution (15 min) sampling, we studied the dynamics of aquatic dissolved and particulate organic carbon (DOC and POC) export through episodic discharge events in a small pristine rainforest catchment in northeast Australia between November 2009 and March 2010. High temporal resolution using this instrumentation requires extensive calibration with concurrent field sampling. The concentration of DOC and POC peaked during times of high stream discharge, reflecting an increased mobilization of soil-water carbon stocks. DOC was the major form of organic carbon in the stream (, 70% of the total carbon export). The majority of total organic carbon exported from the catchment (84%) occurred during significant discharge events (discharge . 50 L s 21 ), which occurred only 9% of the time. Export of DOC and POC totaled 195 and 68 kg km 22 month 21 , respectively, with a DOC : POC ratio of 2.9 6 0.9. If this subcatchment was sampled at weekly intervals the lateral export of carbon would have been underestimated by between 49% and 78% for DOC and POC, respectively. Preliminary d 13 C and molar C : N values of the dissolved and particulate matter suggest that during discharge events, less microbially processed material from the upper soil layers dominated organic matter export, with the opposite being true in nonflood conditions. Not only will the quantities of organic matter exported change in different discharge conditions, but the source and quality may also shift. This study reveals that a field-portable instrument for DOC and POC quantification can yield robust, high-temporal-resolution carbon budget estimates, though detailed, site-specific calibration is essential.