Marshall C. Lamb

Biochar: A Synthesis of Its Agronomic Impact beyond Carbon Sequestration

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

Sexual Reproduction in Aspergillus flavus Sclerotia Naturally Produced in Corn

Aspergillus flavus is the major producer of carcinogenic aflatoxins worldwide in crops. Populations of A. flavus are characterized by high genetic variation and the source of this variation is likely sexual reproduction. The fungus is heterothallic and laboratory crosses produce ascospore-bearing ascocarps embedded within sclerotia. However, the capacity for sexual reproduction in sclerotia naturally formed in crops has not been examined. Corn was grown for 3 years under different levels of drought stress at Shellman, GA, and sclerotia were recovered from 146 ears (0.6% of ears). Sclerotia of A. flavus L strain were dominant in 2010 and 2011 and sclerotia of A. flavus S strain were dominant in 2012. The incidence of S strain sclerotia in corn ears increased with decreasing water availability. Ascocarps were not detected in sclerotia at harvest but incubation of sclerotia on the surface of nonsterile soil in the laboratory resulted in the formation of viable ascospores in A. flavus L and S strains and in homothallic A. alliaceus. Ascospores were produced by section Flavi species in 6.1% of the 6,022 sclerotia (18 of 84 ears) in 2010, 0.1% of the 2,846 sclerotia (3 of 36 ears) in 2011, and 0.5% of the 3,106 sclerotia (5 of 26 ears) in 2012. For sexual reproduction to occur under field conditions, sclerotia may require an additional incubation period on soil following dispersal at crop harvest.

MOISTURE CONTENT DETERMINATION FOR IN-SHELL PEANUTS WITH A LOW-COST IMPEDANCE ANALYZER AND CAPACITOR SENSOR

Moisture content (MC) in peanuts is an important parameter to be measured and monitored at various stages in the peanut industry. In previous research, peanut MC was estimated by placing a sample between a set of parallel-plate conductors to measure capacitance and phase angle of the system with commercially available, expensive impedance analyzers. In this work, a low-cost impedance analyzer called the CI meter (Charis impedance meter) was designed and developed to measure impedance and phase angles at frequencies 1, 5, and 9 MHz using the parallel-plate sensor. The average MC values predicted by the CI meter for peanut samples harvested during two different years were compared with the standard air-oven values. In-shell peanut sample MC ranged between 6% and 23%. Over 90% of estimated in-shell MC values were within 1% of the air-oven values. Ability to determine the average MC of in-shell peanuts without shelling and cleaning them can be of considerable use in the peanut industry.

Economic Returns of Irrigated and Non-Irrigated Peanut Based Cropping Systems

Proper crop rotation is essential to maintaining high peanut yield and quality. However, the economic considerations of sustainable cropping systems must incorporate commodity prices, production costs, and yield responses of the crops within the cropping system. Research was conducted at the USDA/ARS National Peanut Research Laboratorys Multi-crop Irrigation Research Farm in Shellman, Georgia to determine the average net returns of irrigated and non-irrigated cropping systems consisting of peanut (Arachis hypogea L.), cotton (Gossypium hirsutum L.), and corn (Zea mays L.). Five replicated cropping systems provided data on yield responses from irrigated and non-irrigated rotation sequences defined as: continuous peanuts (PPP), cotton/peanuts/cotton (CPC), corn/peanuts/corn (MPM), cotton/cotton/peanuts (CCP), and cotton/corn/peanuts (CMP). The peanut yield in the PPP rotation was 3300 kg/ha in the non-irrigated treatment. Non-irrigated yields in CPC and MPM rotation sequences were 3940 and 3890 kg/ha, respectively and yields in CCP and CMP rotation sequences were 4770 and 4710 kg/ha, respectively. The peanut yield in the PPP rotation was 4080 kg/ha in the irrigated treatment. Irrigated yields in CPC and MPM rotation sequences were 5280 and 5230 kg/ha, respectively and yields in CCP and CMP rotation sequences were 5940 and 6010 kg/ha, respectively. The economic returns of the cropping systems were analyzed for 3 different price level combinations. Production costs (variable and fixed) were obtained from partial budgets. Returns were defined as the 3 year average net returns of each cropping system and were calculated for each price level combination which resulted in 57 comparable average net returns for the irrigated and non-irrigated treatments. Net returns were influenced by rotation sequence, price, and irrigation.

IMPROVING PEANUT YIELD AND GRADE WITH SURFACE DRIP IRRIGATION IN UNDULATING FIELDS

A surface drip irrigation system was developed to irrigate peanut in two experimental fields: one with very little topographic variation on Greenville fine sandy loam soil, and one with undulating terrain containing 2.4% slope on Faceville fine sandy loam soil. Pod yield, kernel size distribution, and total sound mature kernels (TSMK) were evaluated with two peanut varieties, two planting patterns, and two drip tape lateral spacings. Test results were compared with the adjacent non-irrigated area planted with the same varieties of peanut. Soil temperature and volumetric water content were measured at different locations to monitor soil temperature and water movement from drip tapes. Maximum soil temperature in the irrigated area was substantially lower than in the non-irrigated area. For both 13 and 25 mm irrigations, about 16 h were required for water to move laterally 46 cm to reach the peak water content level. No significant difference (p < 0.05) was observed in yields between 0.9 m and 1.8 m drip tape lateral spacings. Peanut yields with drip irrigation were 1.4 times those of the non-irrigated yield. The irrigation water use efficiency from surface drip irrigation was 10 kg/ha-mm during the two growing seasons. Yields tended to slightly decrease as the land elevation decreased for both irrigated and non-irrigated zones. Compared to the non-irrigated areas, the drip-irrigated area produced a greater portion of larger kernels than smaller kernels. In the undulating area, the average TSMK was 73.7% and 64.9% for drip-irrigated and non-irrigated treatments, respectively. Average gross revenue was

Interaction of Tillage System and Irrigation Amount on Peanut Performance in the Southeastern U.S

2,093 per ha with drip irrigation and

Characterization of small RNA populations in non-transgenic and aflatoxin-reducing-transformed peanut

1,253 per ha with no irrigation.

Impact of Sprinkler Irrigation Amount on Peanut Quality Parameters

Abstract A five-year study to investigate the potential interaction of conservation tillage with reduced irrigation amounts was conducted near Dawson, GA on peanut (Arachis hypogaea L.). Conventional tillage was compared to two conservation tillage programs (wide-strip and narrow-strip tillage) under four irrigation levels (100, 66, 33, and 0% of a recommended amount). Peanut yield did not exhibit a tillage by irrigation interaction as expected, although the main effects of irrigation and tillage were each significant by year due to weather variations. Peanut yield in narrow-strip tillage or wide-strip tillage were individually superior to conventional tillage in three seasons out of five, however only in one year did both conservation tillage systems outperform the conventional system. No detrimental effects on yields could be attributed to conservation tillage. Peanut quality and digging loss were dependent on the tillage by year effect as well as the main effect of irrigation. Irrigation increased tota...

Disease Management and Variable Planting Patterns in Peanut

Aflatoxin contamination is a major constraint in food production worldwide. In peanut (Arachis hypogaea L.), these toxic and carcinogenic aflatoxins are mainly produced by Aspergillus flavus Link and A. parasiticus Speare. The use of RNA interference (RNAi) is a promising method to reduce or prevent the accumulation of aflatoxin in peanut seed. In this study, we performed high-throughput sequencing of small RNA populations in a control line and in two transformed peanut lines that expressed an inverted repeat targeting five genes involved in the aflatoxin-biosynthesis pathway and that showed up to 100% less aflatoxin B1 than the controls. The objective was to determine the putative involvement of the small RNA populations in aflatoxin reduction. In total, 41 known microRNA (miRNA) families and many novel miRNAs were identified. Among those, 89 known and 10 novel miRNAs were differentially expressed in the transformed lines. We furthermore found two small interfering RNAs derived from the inverted repeat, and 39 sRNAs that mapped without mismatches to the genome of A. flavus and were present only in the transformed lines. This information will increase our understanding of the effectiveness of RNAi and enable the possible improvement of the RNAi technology for the control of aflatoxins.

Corn and Cotton Yield with Two Surface Drip Lateral Spacings

Abstract Peanut quality parameters were analyzed across four irrigation levels during the 2002 through 2007 crop years. The peanut quality parameters consisted of total sound mature kernels and sound splits (farmer stock grade), shelling outturn by commercial edible size, accept and reject kernels by commercial edible size, seed germination, and aflatoxin. The four irrigation levels consisted of a full level (100%), two reduced levels (66% and 33%), and a non-irrigated control. The research was conducted at the USDA/ARS National Peanut Research Laboratorys Multi-crop Irrigation Research Farm in Shellman, Georgia. By year, significant differences in the irrigation treatments depended upon precipitation distribution for the specific quality parameters. For the average over the six years in the study, farmer stock grade was not significantly different in the 100, 66, and 33% treatments while all were significantly higher than the non-irrigated control. Total shelling outturn and total edible outturn were hi...