Wheat grown after Brassica crops normally yields more than wheat grown after wheat. Previously we reviewed 33 experiments and concluded that wheat after canola yielded about 19 % more than wheat after wheat and that the gross margin of a canola-wheat sequence was 27 % greater than a wheat-wheat sequence. Further analysis of other published, replicated experiments revealed that the mean increase in wheat yield after brassicas was better represented as a fixed amount rather than a percentage. The mean yield benefit of canola (B napus) to subsequent wheat yield was similar (0.8 t ha-1) over 180 experiments where wheat yield varied from 1.1 to 9.5 t ha -1. Over 36 experiments where canola and juncea canola (B juncea) were compared the break-crop effects were identical at 0.6 t ha -1 . Part of the reason for the additional wheat yield is increased uptake of soil water and nutrients, which may explain the fixed, rather than percentage, increase in mean yield as a response to the limited supply of these resources. The earlier conclusion about canola-wheat providing a 27 % increase in gross margin over wheat-wheat must be revised since the financial benefit is relatively greater at low levels of wheat yield. A canola-wheat sequence provided an 85% increase in gross margin over wheat-wheat at low (2 t ha -1 ) yield levels but only 3% at high (6 t ha -1 ) yield levels.

No abstract

A database of global agricultural primary production has been constructed and used to estimate its energy content. The portion of crops available for food and biofuel after postharvest losses was evaluated. The basic conditions for agriculture and plant growth were studied, to ensure sustainable scenarios regarding use of residues. The available energy contents for the world and EU27 was found to be 7,200-9,300 and 430 TWh, respectively, to be compared with food requirements of 7,100 and 530 TWh. Clearly, very little, or nothing, remains for biofuel from agricultural primary crops. However, by using residues and bioorganic waste, it was found that biofuel production could theoretically replace one-fourth of the global consumption of fossil fuels for transport. The expansion potential for global agriculture is limited by availability of land, water, and energy. A future decrease in supply of fossil energy and ongoing land degradation will thus cause difficulties for increased biofuel production from agriculture.

No abstract

No abstract