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Brassicaceae oilseed crops can provide rotation benefits to dryland wheat (Triticum aestivum L.) and supply feedstock for biofuel production. However, growers face decisions about what oilseed crop is best suited for an environment. The objective of this study was to determine how varying production environments affect the agronomic performance of modern cultivars of six Brassicaceae crop species and identify ideal genotypes for seven growing environments spanning four ecoregions. A field experiment was replicated in Colorado, Idaho, Iowa, Minnesota, Montana, North Dakota, and Oregon, USA, between 2013 and 2016 to measure seed and oil yields of seed for four cultivars of Brassica napus, two of B. carinata, two of B. juncea, two of Sinapis alba, one of B. rapa, and one of Camelina sativa. Also, δ13C signature of seed was used as an indicator of water limitation. Generally, across all genotypes, seed and oil yields increased with increased growing season precipitation. Modern commercial cultivars of B. napus and B. juncea had the highest seed oil contents and generally produced the greatest oil yields across most environments, although they were not always the highest seed yielders. For instance, B. carinata over six site years in North Dakota and Minnesota yielded greater than B. napus producing as much as 2471 kg ha−1 in Minnesota. Camelina produced competitive seed yields in some of the drier environments and its δ13C signature indicated that it had the greatest drought resistance. However, seed oil content of some of these high yielding genotypes may need improvement before they are viable as biofuel feedstock. [ABSTRACT FROM AUTHOR]

Mineralization of soil organic matter is governed by predictable factors with nitrate-N as the end product. Crop production interrupts the natural balance, accelerates mineralization of N, and elevates levels of nitrate-N in soil. Six factors determine nitrate-N levels in soils: soil clay content, bulk density, organic matter content, pH, temperature, and rainfall. Maximal rates of N mineralization require an optimal level of air-filled pore space. Optimal air-filled pore space depends on soil clay content, soil organic matter content, soil bulk density, and rainfall. Pore space is partitioned into water- and air-filled space. A maximal rate of nitrate formation occurs at a pH of 6.7 and rather modest mineralization rates occur at pH 5.0 and 8.0. Predictions of the soil nitrate-N concentrations with a relative precision of 1 to 4 microg N g(-1) of soil were obtained with a computerized N fertilizer decision aid. Grain yields obtained using the N fertilizer decision aid were not measurably different from those using adjacent farmer practices, but N fertilizer use was reduced by >10%. Predicting mineralization in this manner allows optimal N applications to be determined for site-specific soil and weather conditions.