| Qingyang city of Gansu Province is located in the western of the Loess Plateau, where winter wheat is mainly mono-cultured with low resource utilization and poor rural economic income. With the development of sustainable agriculture and demand to improve famer incomes, integrated crop and livestock industry has become a significant part of agricultural systems and its output value has increased to 1180 million Yuan. However, lack of quality forage has become a bottle-neck in the development of high-efficiency and high quality livestock products. Due to the high yield and good quality, annual crops are consided to be a logical solution to relieving the forage shortage in spring and winter. Accordingly, this experiment was conducted under spring and summer sown condition in the Longdong Loess Plateau for 4 years to explore the optimum production pattern of annual forage crops. Dry matter (DM), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), digestible dry matter (DDM), digestible dry matter intake (DMI), relative feed value (RFV) and water use efficiency (WUE) were used as indicators in a model which applied Grey Correlative Degree analysis to comprehensively evaluate the production characteristics of annual forage crops under different sowing season. The APSIM model was used to forecast the potential production of annual forage crops under fully soil water profile and no-limiting nitrogen conditions. The main results of this study are listed as below.1. Spring-sown experiment was conducted in the years 2009 and 2010. Spring wheat had the highest dry matter than the others at 42 days after emergence (DAE) (P<0.05), maize and sudan grass had the highest dry matter of 11 t ha-1 and 9 t ha-1 at 105 DAE, respectively. Spring wheat is the optimum selection for forage production at early spring time, during autumn and winter, with maize and sudan grass being the best selection to solve the forage shortage problem. Among the 9 forage species, legumes had the consistent highest crude protein content, the lowest ADF and NDF content compared with the graminoid species throughout the whole growing season in both 2 years. Water use efficiency of DM (WUEDM) of maize was reached to 40 kg ha-1mm-1, which was significantly higher than the other species (P<0.05), followed was sudan grass; WUERFV and WUEcp showed similar trends in both 2 seasons. Maize had the highest WUERFV, and sudan grass was followed; soybean had the highest WUEcp and maize was followed. The optimal annual forage crops were maize, sudan grass and soybean according to the WUEDM, WUECP and WUERFV.According to the Logistic model, the vigorous growth period of maize, sudan grass, small millet, millet, soybean, vetch, pea, oats and spring wheat was 84,75,83,75,83,62,58,63, and 62 d after emergence, respectively. The optimal production pattern was that spring wheat was used in May, and maize, sudan grass and soybean were used for silage or hay.2. summer-sown experiment was conducted in the years 2012 and 2013. DM of sudan grass reached 8.3 t ha-1, which was significantly higher than the other crops at 84 DAE under autumn sowing condition in the year of 2012 and 2013 (P<0.05), and pea followed. Our results indicated that the optimal forage was sudan grass and pea based on DM production. Acording to the nutritive value of annual forage crops, soybean, vetch and pea were much better than the others, which was similar to the spring sowing condition. The WUEDM for sudan grass was significantly higher than others in both seasons (P<0.05) followed by pea; WUEcp for oats was higher than others (P<0.05), with pea following; WUERFV for pea was significantly higher than others (P<0.05), with oats following. Our results indicated that the optimal annual forage crops were sudan grass, oats and pea according to the WUEDM, WUECP, and WUERFV.According to the logistic model, the vigorous growth period of sudan grass, small millet, millet, soybean, vetch, pea, oats and spring wheat was 51,66,49,55,59,39,57 and 61 d after emergence, respectively. The optimal production pattern is that oats is used in August, then sudan grass and pea is used in September.3. An evaluation system was formed basing on Grey Correlative Degree analysis, which is used to confirm the grade of the evaluation object. Entropy method was used to measure weight value. Our results showed that the weight value of DDM was highest, followed by ADF, with DM being lowest under both spring and summer sown conditions. According to the comprehensive evaluation, soybean and maize were proven to be the optimal crops under spring-sowing, and pea, soybean and sudan grass were proven to be optimal under summer-sowing. Both under spring and winter sowing conditions, the results showed that weighted Grey Correlative Degree (WGCD) evaluation and Grey Correlative Degree (GCD) evaluation obtained similar results.4. Based on APSIM modeling similation, the relationships between simulation value and observed value of soil water and biomass were significantly positive. Soil water and biomass of maize were most accurately described by APSIM model, followed by spring wheat, and oats was least accurately described. The potential production of maize, millet, oats and spring wheat were 15.2 t ha-1,6 t ha-1,9.8 t ha-1 and 11.2 t ha-1, compared to the production of traditional planting pattern, which increased 33.6%,37.3%,117% and 169%.The results suggest the optimum utilization period under spring and autumn sowing. Crude protein production-WUE (WUEcp) and relative feed value production WUE (WUERFV) was first proposed in this study, and the production performance of annual forage crop comprehensively evaluated; the production and quality characteristics of forage were coupled; the optimal production pattern and production potential of annual forage crops in Longdong Loess Plateau was proposed based on the APSIM modeling results. The results are of great importance to the development of crop-livestock system, and the increase of production and income of farmer and the improvement of resource use efficiency. |
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