by kublikhan » Mon 23 May 2011, 02:08:49
$this->bbcode_second_pass_quote('sparky', 'G')oing to a sustainable agriculture cost a lot
crop rotation on a three field system ,production decreased by two third without phosphates and Nitrogen losses of 10% average without pesticide and fungicide on a good year on a bad one that's half or plus of the harvest gone. so that's 90% of one third of one third or ten percent forget food export
Source? My sources(in my above post) are saying the switch to sustainable agriculture resulted in an average yield increase of 80%, not that huge drops in yield that you are claiming. A second source claims an increase of 32% after switching away from conventional agriculture. In the first few years, yields often drop during the transition phase. But after a few years, yields are back over conventional agriculture. And in another long term study, a comparison found the yields roughly equal to conventional agriculture, except in drough years where conventional agricuture suffered because of it's soils lowered ability to retain water.
$this->bbcode_second_pass_quote('', 'I')n other words, organic agriculture is on average 32.1 percent more productive than conventional agriculture. Furthermore, green manure alone provides more than enough nitrogen, amounting to 171 percent of synthetic N fertilizer used currently.
Similarly, a seven year-long field experiment carried out with farmers in Ethiopia found that crops fed with organic compost out-yielded chemically-fertilized crops, the O/C ratio averaged over the four most commonly grown grain crops was 1.34 [12] (see Table 1). Thus, organic production again increased yields by about 30 percent.
Kathleen Delate of Iowa State University and Cynthia Cambardella of the US Department of Agriculture assessed the performance of farms switching from conventional to certified organic grain production [13, 14]. The experiment lasted four years: three years of transition to organic and first year of certified organic growth. They found that over the four years, corn yield in the organic system averaged 91.8 percent of conventional corn yield, and soybean in the organic system averaged 99.6 percent of conventional soybean yield. The small reductions in yields were due to bigger reductions during the first and second years of transition. By the third year, there were no significant differences in yields, but by the fourth year, both organic corn and soybean yields exceeded conventional yields. In the initial year of transition, an economic advantage could be gained by planting legume hay crops or crops with a low nitrogen demand in fields with low productivity, in order to increase fertility for the following corn crop. In the second year, yield differences were mitigated by rotation and compost application, providing sufficient nutrients for the organic grain crop. The importance of a soil-building cover crop, or legume grass mixture such as the oat-alfalfa mixture was apparent in the fourth year, when organic corn and soybean out-yielded the conventional crops.
Delate has been maintaining the 17 acre Long Term Agroecological Research site in Greenfield, Iowa, for the past 12 years, experimenting on four different rotation systems and comparing organic and conventional yields [15]. In the fourth year of the latest experiment, organic corn yields averaged across all rotations was 130 bushels per acre compared with the conventional corn yield of 112 bushels per acre. Organic soybean yields averaged 45 bushels/acre, exceeding the conventional yield of 40 bushels/acre. Over the 12 years of the experiment, the average corn yields are 171 bu/ac and 163 bu/ac for organic and conventional respectively. The 12 year average yields for organic and conventional soybeans are identical at 47 bu/ac.
A long-term field trial at Rodale Institute in Kutztown, Pennsylvania involving 6.1 ha compared three different cropping systems: conventional, animal manure and legume-based organic, and legume-based organic. The results over 13 years showed that organic yields were not different from conventional, except in drought years, when organic yields were 28 to 34 percent higher than conventional [17, 18]. Organic soils holds more water, and water percolating through into the soil was 15 to 20 percent greater in organic soils.