A gronomy J our n al • Volu me 102 , I s sue 2 • 2 010 623 ABSTRACT Pyrolysis is the anaerobic thermal conversion of biomass for energy production. It off ers an option of returning carbon and nutrients to the soil while producing energy. Th e Ultisols in the southeastern United States have inherently low soil organic carbon and fertility, and may benefi t from the addition of biochar from pyrolysis. Our objectives were to evaluate the eff ect of peanut hull and pine chip biochars on soil nutrients, corn (Zea mays L.) nutrient status and yield in a Kandiudult for two growing seasons (2006 and 2007). Experiments for each biochar source were conducted as completely randomized designs with the biochar applied at 0, 11, and 22 Mg ha -1 with and without N fertilizer. Nitrogen in the peanut hull biochar (209 kg ha -1 at 11 Mg ha -1 rate) was not available during the study based on corn tissue concentrations. Th e peanut hull biochar linearly increased Mehlich I K, Ca, and Mg in the surface soil (0-15 cm). Th e increased available K was refl ected in the plant tissue analysis at corn stage R1 in 2006, but not in 2007. Pine chip biochar decreased soil pH, but had no eff ect on other nutrients except Mehlich I Ca. In the peanut hull biochar experiment, grain yields decreased at the 22 Mg ha -1 rate in the fertilized treatments. In the pine chip biochar experiment, grain yields decreased linearly with application rate in 2006, but this did not persist in 2007. Overall yield responses to biochar were smaller than expected based on previous studies.

Summary Intensively managed pine plantations in the south‐eastern United States can play an important role in global carbon sequestration both through accumulation of carbon in wood used in long‐lasting products as well as through increased soil carbon storage. Fertilization and understorey‐elimination are two commonly used intensive management practices in the south‐eastern United States that have the potential to increase carbon storage in vegetation and affect soil carbon. In this study, we assessed the effects of these practices on carbon accumulation in vegetation biomass and in the soil of 17‐year‐old slash pine Pinus elliottii plantations in the flatwoods of northern Florida, USA. Three treatments, fertilization, understorey‐elimination, and fertilization plus understorey‐elimination, were evaluated and compared with an untreated control. All three treatments increased above‐ground biomass accumulation compared with the untreated control; understorey‐elimination also increased biomass of the forest floor litter, with or without fertilization. Although understorey‐elimination increased above‐ground production, as a result of reduced below‐ground production total net primary production was decreased in plots from which the understorey was eliminated. Soil carbon storage was lower in plots where the understorey was eliminated, with or without fertilization. This appeared to be the result of reduced fine root growth and mortality but also may have reflected reduced litterfall inputs early in the rotation. Our results indicate that intensive management of pine plantations on sandy flatwoods soils can increase carbon sequestration, but these increases will be the result of increased carbon accumulation in biomass and its long‐term uses rather than through increased soil carbon.

No abstract

Throughout the Amazon of Brazil, manioc (Manihot esculenta) is a staple crop produced through slash-and-burn agriculture. Nutrient losses during slash-and-burn can be large and nutrient demand by food crops so great that fields are often abandoned after two years. In recent decades, farmers have reduced the fallow phase from 20 to *5 years, limiting plant nutrient accumulation to sustain crop yields. Improved fallows through simultaneous planting of trees with food crops may accelerate nutrient re-accumulation. In addition, slash-and-mulch technology may prevent loss of nutrients due to burning and mulch decomposition may serve as a slow-release source of nutrients. This study in Pará, Brazil, in a 7-year-old secondary forest following slashing and mulching of the vegetation, involved two main plot treatments (with and without P and K fertilizers) and two sub-plot treatments (with or without a N 2 -fixer Inga edulis). A mixed-culture of trees and manioc was planted in all plots. P and K fertilizer increased tree mortality due to weed competition but growth of surviving trees in four of the five tree species tested also increased as did biomass production of manioc. In the N 2 -fixer treatment trends of greater growth and survival of four of five tree species and manioc biomass were also observed. Fertilization increased the biomass of competing vegetation, but there was a fertilizer by N 2 -fixer interaction as I. edulis caused a reduction in competing biomass in the fertilized treatment. After one year, fertilization increased decomposition of the mulch such that Ca, Mg, and N contents within the mulch all decreased. In contrast, P and K contents of mulch increased in all treatments. No influence of the N 2 -fixer on 0-10 cm soil N contents was observed. Two years after establishment, this agroforestry system succeeded in growing a manioc crop and leaving a well-maintained tree fallow after the crop harvest.

A rhizotron study was conducted to assess the relationship between soil water availability and shoot and root growth of loblolly pine (Pinus taeda L.) under conditions where O2 availability and mechanical resistance were considered not limiting. Relationships between soil water availability and (i) root growth rate, (ii) root distribution, (iii) growth periodicity, and (iv) above‐ and belowground allocation were evaluated under four watering regimes ranging from maintaining profile near field capacity (WK 1) to withholding moisture for 4 wk (WK 4). The final distribution of cumulative root growth was similar among watering treatments, even though root growth shifted downward with depth during the growing period due to water depletion in surface soils. Relative root elongation rates were found to be linearly related to soil water potential. The strength of this relationship was improved by considering only periods of active root growth. Reductions in above‐ and belowground growth were proportional among water‐restricting treatments. Stem volume and root growth in the driest treatments were reduced 46 and 41%, respectively, compared with the WK 1 cells, indicating that patterns of biomass allocation above and below ground were similar among treatments. In the absence of other limiting soil factors, flushes of root growth in this study were a function of relatively short‐term changes in soil water potential. Our results indicate that when maximum tree biomass is desired, management efforts in establishing pine should be aimed at reducing any restrictions to root growth during establishment.

Surface application of urea to pine forests may lead to ammonia (NH3) loss. It is generally believed that rainfall received soon after urea application will wash the urea and its hydrolysis products into the soil and stop NH3 loss, but quantitative data are lacking, especially for the forest environment. The objective of this study was to quantify the effect of rainfall on loss of NH3 when received at different times following urea application. Four field studies were performed in a midrotation loblolly pine (Pinus taeda L.) plantation, where NH3 volatilization chambers were fertilized with 200 kg ha−1 N and NH3 losses were measured for either 29 or 58 d. In a complementary lab study, both NH3 loss and movement of fertilizer N into the soil were measured following simulated rain. Loss of NH3 from urea was either increased or not affected by simulated rainfall applied after the urea granules were dissolved by dew. Increased NH3 loss due to simulated rainfall was attributed to inefficient downward leaching of urea and increased water content, which is known to increase the rate of urea hydrolysis. In contrast, simulated rainfall applied immediately after urea application reduced NH3 losses to <1% of the applied urea. Our results show that unless rain occurs before urea is dissolved by morning dew, it may not be effective at leaching urea into the soil and reducing NH3 losses. Further research should be conducted to elucidate the mechanism of urea retention by the O horizon in pine forests.

Rigid control has been imposed upon the Missouri River by impounding over one-half of the upper 1500 miles and by channeling most of the remaining river within permanent, narrow banks. These controls have caused environmental changes in the lower Missouri River, as shown by this study, of adjacent unchannelized and channelized sections of river below the main stem impoundments. Impoundments have regulated flow by evening maximum and minimum discharges and improved downstream water quality by decreasing turbidity and indirectly raising the dissolved oxygen. In addition the impoundments have contributed a limnetic cladoceran, Leptodora kindti, to the drift and have affected the distribution of benthos through the modification of turbidity. Channelization of the river has reduced both the size and variety of aquatic habitat by destroying key productive areas. Average standing crops of benthos were similar in un-channelized and channelized river (0.63 and 0.67 pounds per acre, respectively) but the benthic area had been reduced 67% by channelization. In the channelized river the average standing crop of drift was 8 g per acre-foot while in the unaltered river the average standing crop was 68 g per acre-foot. There was little similarity between the organisms of the drift and benthos; however there was similarity between the organisms in the drift and the aufwuchs.

No abstract