| On the one side, wheat-based double cropping system in hebei plain cost mass water resource, which was the key factor of "non-sustainable" developing agriculture. On the other side, it plays an important role in the protection of regional and national food security. Understanding the croping system all-around from macroscopical point is of great significance to adjust crop structure scientificly and reasonably. In this paper, using a large sample survey data and model, we analysised the economic efficiency and water economic use effeciency use economic efficiency and erosion-preventing effects of wheat-maize and cotton fields in hebei plain. The result shows:(1) The economic effects of wheat -maize and cotton fields were analyzed using the investigating data from 114 farmers in quzhou county during the year 2004-2005, the rusults showed: the net output of wheat-maize and cotton fields were separetely 10624.3 yuan/hm2 and 13870 yuan/hm2, the net output of wheat-maize and cotton fields were separetely 4174.3 yuan/hm2 and 5520 yuan/hm2, the net prifits in wheat -maize was lower 24.4% than that of cotton.(2) Water economic use efficiency (the profit of water consumption per unit area) was analyzed using meteorologic and survey data. The results showed: Water economic use effeciency of wheat -maize and cotton field were separetely 4.12 yuan/ mm·hm-2 and 7.67 yuan/ mm·hm-2. Water economic use effeciency of wheat -maize was 74.46% of that of cotton. The irrigation water economic use effeciency of wheat -maize and cotton field were separetely 11.13 yuan/ mm·hm-2 and 36.80 yuan/ mm·hm-2. The irrigation water economic use effeciency of wheat -maize was 30.25% of that of cotton.(3) We established a new modle on the basis of EPIC model to estimates the amount of wind erosion on farmland. The main parameters of the model included the amount of potential wind erosion, vegetation cover, soil erodibility, surface roughness, block width and surface soil moisture.Using meteorologic data and the relationship between the average wind speed and amount of wind erosion, we estimated the amount of potential wind erosion. And using the value on eroding wind of 2m hight and the relationship among different high-speeds, we calculated the value of eroding wind of meteorological station, 6.94m/s. The result of analysising meteorological data showed, the days of eroding wind in winter-spring season was 82.35% of that of the annual volume, and the amount of potential wind erosion in winter-spring season was 68.62% of that of the annual volume.We estimated the value of vegetation using the LAI obtained from the field experiment and the relationship equation between vegetation cover and the crops leaf area index; and then we calculated the amount of wind erosion by the relationship equation between vegetation cover and the the amount of wind erosion; The result showed: the amount of wind erosion rised by planting wheat-maize was 2% of that of bare farmland, but the amount of wind erosion by planting cotton in winter-spring season was 100% of that of bare farmland, the amount of wind erosion rised by planting wheat-maize was 40% of that of bare farmland from June to July and from October to November, but the amount of wind erosion rised by planting cotton was 3% of that of bare farmland. Therefore, the erosion-preventing effect of wheat-maize was better than that of cotton fields.We estimated surface soil moisture the relationship equation between surface soil moisture and profile soil moisture calculated penman formula and farmland water balance equation. The resulted showed: the amount of wind erosion rised by planting wheat-maize and cotton was merely 0, because the surface soil water of wheat-maize and cotton fields was more than 10%. And the amount of wind erosion rised by planting wheat-maize was larger than that of cotton fields from November to next year April, because surface soil moisture of cotton fields was in the annual minimum value. Therefore, the erosion-preventing effect of wheat-maize was better than that of cotton fields.We revised the ralathionship equation between land surface roughness and the amount of wind erosion according to the value of the amount of wind amount of wind erosion correspond to initial land surface roughness. And then we calculated the value of the amount of wind erosion by the value of land surface roughness estimated by the relationship between land surface roughness (Z0) and the diameter of soil particles and the ralationship of different tillage. The result showed: the land surface roughness of wheat-maize fields with straw stalk cover and the cotton fields with firewood was the biggest, Z0 was 22.1cm and 19.32cm, FR was 0, the erosion-preventing effects was the biggest; the no-tillage wheat-maize and cotton fields was next, Z0 was 13cm, FR was 0; And then it was conventional cultivation wheat-maize fields (straw stalk also field) and cotton fields (rotary + ploughing), Z0 was 0.52cm and 0.58cm, FR was 26% and 25%, it was planting wheat-maize and cotton that reduced 76 and 76% of the amount of wind erosion compared to bare farmland. Z0 of traditional rotary cultivation wheat maize and cotton fields was 0.45cm, which could reduces 65% of amount of wind erosion compared to bare farmland.We tested the new modle with the experimental data of two different places. The result showed: the effect of the new modle was good, which achieved 5% remarkable level.(4) We estimated the amount of wind erosion by the new modle, the result was that the amount of wheat-maize fields was 100.7 kg/hm2, and that the amount of cotton fields was 1603.6 kg/hm2. the value on the amount of wheat-maize fields was 6.2% of the value on the amount of cotton fields. Moreover, the economic loss rised by soil nutrient outflow of wheat- maize fields was 0.77 Yuan /hm2. and the economic loss rised by soil nutrient outflow of cotton fields was 12.21 Yuan /hm2.In summary, in Hebei plain, the wheat - maize field's net output value of unit area,the profit and the water economic use efficiency were lower than that of the cotton field, but wind erosion-resisitence effect is higher than that of the cotton field by far. |
