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.

Anecdotal accounts regarding reduced US cropping system diversity have raised concerns about negative impacts of increasingly homogeneous cropping systems. However, formal analyses to document such changes are lacking. Using US Agriculture Census data, which are collected every five years, we quantified crop species diversity from 1978 to 2012, for the contiguous US on a county level basis. We used Shannon diversity indices expressed as effective number of crop species (ENCS) to quantify crop diversity. We then evaluated changes in county-level crop diversity both nationally and for each of the eight Farm Resource Regions developed by the National Agriculture Statistics Service. During the 34 years we considered in our analyses, both national and regional ENCS changed. Nationally, crop diversity was lower in 2012 than in 1978. However, our analyses also revealed interesting trends between and within different Resource Regions. Overall, the Heartland Resource Region had the lowest crop diversity whereas the Fruitful Rim and Northern Crescent had the highest. In contrast to the other Resource Regions, the Mississippi Portal had significantly higher crop diversity in 2012 than in 1978. Also, within regions there were differences between counties in crop diversity. Spatial autocorrelation revealed clustering of low and high ENCS and this trend became stronger over time. These results show that, nationally counties have been clustering into areas of either low diversity or high diversity. Moreover, a significant trend of more counties shifting to lower rather than to higher crop diversity was detected. The clustering and shifting demonstrates a trend toward crop diversity loss and attendant homogenization of agricultural production systems, which could have far-reaching consequences for provision of ecosystem system services associated with agricultural systems as well as food system sustainability.

Sustainably balancing biofuel crop production with food, feed, and ber on agricultural lands will require developing new cropping strategies. Double-and/or relay-cropping winter camelina (Camelina sativa L.) with soybean [Glycine max (L.) Merr.] may be a means to produce an energy and food crop on the same land in a single year. A study was conducted between 2009 and 2011 in west central Minnesota to evaluate yields, seed quality, economics, and within-eld energy balance of winter camelinasoybean double-and relay-cropping systems compared with a conventional monocropped full-season soybean. Systems included methods to hasten camelina harvest (e.g., swathing and desiccating) to promote early soybean growth. Camelina seed yields were una ected by cropping system and ranged from 1.1 to 1.3 Mg ha -1 . Relay-cropped soybean yields were greater than doublecropped soybean and were 58 to 83% of that for the monocropped control. Seed oil and protein content of double-and relaycropped soybean were comparable to their monocropped counterpart and combined seed oil yield for the dual crop systems was as much as 50% greater. Net economic returns for the relay-crop treatments were competitive with that of the full-season soybean. Moreover, net energy of the relay-crop treatments was generally as high as the sole soybean crop, but energy e ciency (outputs/ inputs) was less due to greater inputs. Results indicate that dual cropping of winter camelina with soybean is agronomically viable for the upper Midwest and might be an attractive system to growers seeking a "cash" cover crop.

Many environmental benefits accrue from reducing tillage and increasing crop diversity; however, economic factors often encourage the continued use of intensive tillage and specialized crop production. This study examined crop yields, input costs, and economic returns during the transition to a range of cropping system alternatives in the northern Corn Belt region, including different system (organic, conventional), tillage (conventional, strip-tillage), rotation (corn-soybean, corn-soybean-wheat/alfalfa-alfalfa) [Zea mays L., Glycine max (L.) Merr., Triticum aestivum L., Medicago sativa L.], and fertility (no fertilizer/manure, fertilizer/manure applied at recommended rates) treatments. Increasing crop diversity and reducing tillage intensity reduced total costs by $24-102 ha 21 within conventional treatments, and $16-107 ha 21 within organic treatments. Yields of corn, soybean, and wheat were more than 15% lower when using organic vs. the highest yielding conventional practices. Treatments receiving fertilizer or manure had wheat yields more than 0.3 Mg ha 21 and alfalfa yields 2.7 Mg ha 21 higher than treatments that did not receive fertilizer or manure. Within conventional systems, no significant differences in the 4-yr net present value of net returns were detected for tillage and rotation alternatives. Net present values for the organic systems without organic price premiums were at least $692 ha 21 lower than for the best conventional systems suggesting a barrier to the adoption of these systems should organic price premiums decline. However, when organic price premiums were included, most organic treatments had net present values comparable to or exceeding those from conventional treatments.

Conservation agricultural systems rely on three principles to enhance ecosystem services: (1) minimizing soil disturbance, (2) maximizing soil surface cover and (3) stimulating biological activity. In this paper, we explore the concept of diversity and its role in maximizing ecosystem services from managed grasslands and integrated agricultural systems (i.e., integrated crop-livestock-forage systems) at the field and farm level. We also examine trade-offs that may be involved in realizing greater ecosystem services. Previous research on livestock production systems, particularly in pastureland, has shown improvements in herbage productivity and reduced weed invasion with increased forage diversity but little response in terms of animal production. Managing forage diversity in pastureland requires new tools to guide the selection and placement of plant mixtures across a farm according to site suitability and the goals of the producer. Integrated agricultural systems embrace the concept of dynamic cropping systems, which incorporates a long-term strategy of annual crop sequencing that optimizes crop and soil use options to attain production, economic and resource conservation goals by using sound ecological management principles. Integrating dynamic cropping systems with livestock production increases the complexity of management, but also creates synergies among system components that may improve resilience and sustainability while fulfilling multiple ecosystem functions. Diversified conservation agricultural systems can sustain crop and livestock production and provide additional ecosystem services such as soil C storage, efficient nutrient cycling and conservation of biodiversity.

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One-pass harvest equipment has been developed to collect corn (Zea mays L.) grain, stover, and cobs that can be used as bioenergy feedstock. Nutrients removed in these feedstocks have soil fertility implication and affect feedstock quality. The study objectives were to quantify nutrient concentrations and potential removal as a function of cutting height, plant organ, and physiological stage. Plant samples were collected in 10-cm increments at seven diverse geographic locations at two maturities and analyzed for multiple elements. At grain harvest, nutrient concentration averaged 5.5 gN kg −1 , 0.5 gP kg −1 , and 6.2 gK kg −1 in cobs, 7.5 gN kg −1 , 1.2 gP kg −1 , and 8.7 gK kg −1 in the above-ear stover fraction, and 6.4 gN kg −1 , 1.0 gP kg −1 , and 10.7 g K kg −1 in the below-ear stover fraction (stover fractions exclude cobs). The average collective cost to replace N, P, and K was $11.66 Mg −1 for cobs, $17.59 Mg −1 for above-ear Wally W. Wilhelm deceased.The US Department of Agriculture offers its programs to all eligible persons regardless of race, color, age, sex, or national origin and is an equal opportunity employer.The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the US Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. Electronic supplementary materialThe online version of this article (stover, and $18.11 Mg −1 for below-ear stover. If 3 Mg ha −1 of above-ear stover fraction plus 1 Mg of cobs are harvested, an average N, P, and K replacement cost was estimated at $64 ha −1 . Collecting cobs or above-ear stover fraction may provide a higher quality feedstock while removing fewer nutrients compared to whole stover removal. This information will enable producers to balance soil fertility by adjusting fertilizer rates and to sustain soil quality by predicting C removal for different harvest scenarios. It also provides elemental information to the bioenergy industry.

Cover crops can serve as a valuable management tool for improving soil and water quality, but are an added expense for farmers. We evaluated the yields and economics of four cover crops and two winter fallow treatments in a spring wheat (Triticum aestivum L.)-soybean [Glycine max (L.) Merr.] rotation at three sites in Minnesota. The four cover crop treatments were winter rye (Secale cereal L.), forage radish (Raphanus sativus L.), winter camelina [Camelina sativa (L.) Crantz], and pennycress (Thlaspi arvense L.) planted into spring wheat stubble. The fallow treatments consisted of no-tilled and conventionally tilled soil. Radish winterkilled and rye was terminated chemically before planting soybean in early May. Soybean was inter-seeded between rows of camelina and pennycress at the same time it was planted in other treatments. Camelina and pennycress were harvested over soybean seedlings in late June. Camelina yields ranged from 600 to 1100 kg ha -1 , while pennycress ranged from 900 to 1550 kg ha -1 . Mono-cropped soybean averaged 1819, 3510, and 4180 kg ha -1 in northern, central, and southern Minnesota, respectively. Soybean seedlings under oilseed cover crop canopies exhibited lightstress, which likely reduced soybean yield in these treatments by 22 to 30%. When oilseed and inter-seeded soybean yields were combined, total seed yields generally were equal to or exceeded those of mono-cropped soybean. In addition, net income for inter-seeded systems was typically equivalent to mono-cropped soybean. Improvements in net income are likely needed before the benefits of oilseed cover crops are fully realized.• Net income from relay cropping was rarely different from that of mono-cropping. • A 25-cm oilseed row spacing was likely too narrow for optimal soybean growth. • Further domestication of oilseeds will likely improve relay cropping with soybean.