| Modern agriculture empharizes the high production and yields maximization withoutexaming the subsequent consequences, such as soil degradation, pesticide contamination forgroundwater and decling biotic diversity. On the other hand, with arable land consecutivereduction and destruction, the insufficience of food and feed supply for humans and livestockis becoming more and more serious. High yield and sustainability are the cath phrases ofcropping production in21stcentury. Thus, it is essential to seek a available cropping strategeto solve the crisis of food supply, in addition, to ensure the sustainable availability of land andlong-term development of agroecosystem. Intercropping, due to its potential advantages inbiomass yield (grain and residue), reducing of chemical fertilizer and pesticide input, andincreased biodiversity and land sustainability, has been paid unprecedented attention andconsidered to be a feasible strategy to relieve the food and feed crisis. However, littleattention has been paid to the intercropping of perennial legumes with annual cereals althoughintercropping system is widely applied and studied. The main objective of this study was todetermine the aboveground biomass yield and clarify the mechanism of productionperformance from the perspectives of interspecific competitiveness, the root distribution, andbiological N2fixation (Nfix) in different alfalfa (Medicago sativa L.) and corn (Zea mays L.)intercropping patterns, on the other hand, by conducting animal experiment to investigate thenutrients digestibility of mixtures harvested from intercropping system, as well theperformances of nutrients and utilizable nutrients, thus providing the theoretical evidences forthe applications of this intercopping system in practice. A3-year (2007-2009) fieldexperiment was conducted, including four intercropping patterns by alternating alfalfa andcorn row ratios of2:2,3:2,4:2and5:2. Mono-cultured corn and alfalfa were used as thecontrol. The biomass yields of different treatments were measured. The indices ofcompetitiveness involving land equivalent ratio (LER), aggressivity (A), relative crowdingcoefficient (K values), competitive ratio (CR), and the root spatial distribution described by measuring root length density (RLD), nitrogen (N) acquisition, the fixation of N wereexamined. In the animal experiment the nutrients digestibility, nutrients yields and availablenutrients yield were measured. The main resulted were described as follows:1. The biomass yields and interspecific competitiveness of different intercropping treatmentsThe biomass yields of mono-cultured alfalfa and all intercropping patterns increased eachyear. In all years, the5:2intercropping pattern always displayed a biomass yield advantagebased on greater LER values. Alfalfa had higher relative crowding coefficients (K values), CR,and A values than corn. The intercropping of alfalfa with corn had yield advantages comparedto alfalfa or corn monoculture. The intercropping pattern of5:2(alfalfa: corn row ratio) wasan optimal pattern in our study. Alfalfa was the superior competitor when grown with corn,and its productivity dominated the total biomass yields. Thus, intercropping of alfalfa withcorn has the potential to improve performance with high land-use efficiency.2. The root distribution and nitrogen nutrition in alfalfa/corn intercropping systemsThe N acquisition and the Nfix were measured to assess the N nutrient in alfalfa/corncommunity. The alfalfa/corn combination had a N yield advantage over mono-cultured cornbased on higher nitrogen land equivalent ratio (NLER), as well as improved Nfix in the5:2intercropping pattern regardless of stand age. In addition, the aboveground N acquisitionexhibited linear increase with higher alfalfa ratio in intercropping system (5:2>2:2), whereasthe Nfix exhibited a quadratic response to the increased area of alfalfa in alfalfa/cornintercropping. More of the root spread laterally towards the neighboring alfalfa root zone inintercropped corn compared to mono-cultured corn. However, the root mass centre ofintercropped alfalfa descended into deeper soil layers with advancing stand age, and likewiseproliferated laterally towards associated corn rows. The gap between alfalfa and corn rowswas the highest root density area, with greater root intermingling and highest RLD. Thecompatibility and facilitation of intercropped alfalfa and corn roots were the main cause forthe enhanced N acquisition and Nfix.3. The evaluation of feed nutrient values for the mixtures harvested from alfalfa/cornintercopping systemsForm the animal nutrition standpoint, the intercropping system of alfalfa/corn improvedthe digestibility of crude protein, carbohydrate, and gross energy, as well as the yield ofprotein and available protein per hectare land caompared with corn sloe crop. On the otherhand, compared with the mono-cultured alfalfa, the intercropping system notably enhancedthe digestibility and yields of ether extract, carbohydrate, gross energy, at the same time the yield of corresponding available nutrients. The established years did not effect thedigestibility, however, the yield of DM, CP, EE, GE and corresponding available nutrientswere all increased with each year. The diets composed of the mixtures harvested fromintercropping community enhanced the PH values and ammonia nitrogen concentration ofrumen compared with the harvested product from mono-cultured corn. This provided aperfect fermentable environment for microorganisms in rumen, thus the improvedtransformation rate of microbial crude protein and the amount of microorganisms, as well asthe degradation extent of cellulose part of corn and alfalfa stalks.In conclusion, the alfalfa and corn intercropping system had better producingperformances relative to the mono-cultured corn or alfalfa referring to the DM yield andeconomic profit of unit land. From the feed production perspective, the mixed product fromintercropping system had a higher utilization, greater yields of nutrients and availablenutrients, and improved feed production potential compared to the sole cropping. Therefore,the alfalfa and corn intercropping system is a feasible planted pattern for higher feedproduction. |
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