Energy crop cultivation weeds

The assessment of the sustainability of the cultivation of energy crops includes the input and recycling of nutrients, the application of pesticides, the water-use efficiency, the consumption of fossil fuels and the balance of soil carbon. The aim is to recycle the nutrients, which is simple in the case of anaerobic digestion by applying the digestate to the field. If crops are combusted many of the minerals can be returned via the ash. In the case of liquid biofuels, exported nutrients are lost and have to be replaced. The application of pesticides, mainly herbicides, can often be reduced in comparison to food production, but the energy yield per hectare might be reduced if the share of weeds exceeds certain thresholds. Water use efficiency,... 

Flame cultivation was attempted in sugarcane in the 1940s (Conrad and Lucas, 1995), but was soon abandoned. Liquid propane flamers burned broadleaf and grassy weeds as shields partially protected the crop from thermal damage. While flame cultivation was only marginally useful in sugarcane, tractor-mounted weed burners have been important in the transition from dependence on repetitive mechanical cultivation to the concept of chemical energy for weed control. 

From the beginning of recorded history, weeds have limited man s food supply and have imposed a heavy labor burden. Nearly all of early man s time was no doubt spent in obtaining food. Natural food sources permitted man s survival, even though periods of starvation must have been common. From 10,000 B.C. to 6,000 B.C., man began to cultivate crops by primitive methods (Fig. 1) (JL). About 6,000 B.C., he fashioned hand-weeding tools. Around 1,000 B.C., animal-powered implements were introduced. Prior to this time, human energy was the sole source available for weed control. 

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