Screening And Evaluation Of Different Varieties Of Mung Bean As Green Manure

Mung bean (Vigna radiata L.) has rich germplasm resources and is cultivated extensively in China. As one of ancient crops for grain and manure use, mung bean is planted to coordinate soil consumption and fertilization. However, there is little research on mung bean germplasm for green manure use. Through pot experiment, this paper made research on evaluation of green manure effects with 18 summer seeding mung bean varieties. And the evaluation aspects included agronomy, plant and soil nutrients, photosynthesis and shade-tolerance. Through covering mung bean plant in soil and indoor culture, the paper had a further research on mung bean plant decomposition pattern and effects on soil nutrients. The aim was to provide reference for screening, evaluating and utilizing mung bean germplasm for green manure use. Main results were as follows:1. Evaluation of agronomic traits of different mung bean varieties.At flowering-poding stage, root fresh weight, root nodule weight, root nodule amount and the diameter of biggest nodule had high significant positive correlation with plant biomass (p<0.05). Between biomass and height, stem diameter and yield et al. at mature stage, there was significant positive correlation (p<0.01). And plant biomass at the two stages significantly correlated with corresponding growth period (p<0.01). Therefore, plant biomass was the most important index, besides, the growth period also need considered when we evaluate mung bean germplasm as green manure by agronomic traits. There was no difference between flowering-poding and mature stages without seed on plant biomass.2. Evaluation of plant and soil nutrient characteristics of different mung bean varieties.Nitrogen (N), phosphorus (P) and potassium (K) contents of plant at mature stage were significantly higher than that at flowering-poding stage, and C/N ratio was opposite (p<0.01). From plant nutrient accumulation aspect, N and P accumulations at mature stage were significantly higher than that at flowering-poding stage (p<0.01), and there was no difference on K accumulation. Both ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) contents in soil were higher than that at flowering-poding stage significantly, available K was opposite (p<0.01), and there was no difference on available P.3. Evaluation of photosynthetic characteristics of different mung bean varieties.At flowering-poding stage, plant biomass significantly correlated positively with intercellular CO₂ concentration (Ci) and transpiration rate (Tr) (p<0.01). Yield per plant significantly correlated with stomatal conductance (Cond) and Ci (p<0.05). Photosynthetic characteristics could be considered as physiological index when plant biomass and yield were evaluated.4. Evaluation of shade-tolerance of different mung bean varieties.Under shading treatment, except for plant stem-leaf ratio and height increased significantly, photosynthetic indexes and other agronomic indexes such as biomass and yield per plant all decreased. There were significant differences between varieties (p<0.01). Through principal component analysis, the change range of agronomic characteristics such as biomass, branch number, yield and photosynthetic characteristics such as Pn, Ci, and WUE were the principal indexes which were important to evaluate mung bean varieties by shade-tolerance.5. Mung bean plant decomposing pattern and effects on soil nutrients.The decomposition rate of mung bean plant reached 48.35%⁸0.42% after covered in soil for 90 days. Plant decomposed and released nutrients of N, P and K slowly after 30 days. The nutrient release rates ranked with K>N>P. The decomposition rate correlated significantly and negatively with date, growth stage, and stem-leaf ratio, C/N ratio of plant covered (p<0.05). When plant nutrient contents were higher and plant decomposed better, the nutrient released more. The indoor culture experiment indicated that the contents of nitrate N, available P and available K, organic matter in soil increased after 90 days by 37.62%⁴2.08%, 24.56%⁶5.84%, 18.03%⁴2.87%, 6.01%¹5.23% than the control, respectively. Through correlation analysis, under the condition of unchanged temperature and humidity, after long time decomposition, the effects on soil nutrient content of mung bean as green manure mainly correlated with dry weight and total amount of nutrient.6. Comprehensive screening and evaluation of different varieties of mung bean as green manure.Through principal component and cluster analysis of principal evaluation indexes at flowering-poding stage, 18 mung bean varieties were divided four types. The first type including XiLv No.1 and C1549 had better performance on biomass, nutrient accumulations, C/N and shade-tolerance, which could be intercropped with maize or cotton and applied to soil before mound closure. The second type including 10 varieties such as C2032, C0003 et al. had higher biomass and nutrient amounts, lower C/N ratio, middle shade-tolerance, could be as green manure. The third and fourth types had worse performance on the all indexes, were not suitable for application as green manure.Through principal component and cluster analysis of principal evaluation indexes at flowering-poding stage, 18 mung bean varieties were divided five types. The first one including C2032, C0998 and C1271, which had higher biomass, yield and nutrient amounts, lower C/N ratio, but less shade-tolerance, were suitable for application after havest but not good for intercropping. The second type included 11 varieties such as C0827, C0003 et al. which had better performance on the all indexes, were suitable for green manure use. The third type only included C3821 which had bad performance as green manure. The fourth type included Jin Lvdou No.1 only had higher K amount. The fifth type including JiLv No.7 and JiLv No.8 had lower values on biomass, yield and nutrient amounts, but higher shade-tolerance, which were suitable for intercropping or as catch crop, better as grain than green manure.