| Little precipitation and severe soil erosion seriously restrict increment of agricultural productivity in the dryland of Loess Plateau. With characteristics of drought resistance, barren tolerance and short growth period, broomcorn millet is one of the main cultivated crops in this region. However, extensive cultivation management and backward farming techniques lead to low and unstable yield of broomcorn millet in recent years. Therefore, how to gradually improve the yield and grain quality becomes a key in the production practice of broomcorn millet in this region.The field experiment was conducted at the experimental demonstration base for minor grain crops in Yulin in Shaanxi province from 2011 to 2013, and utilized a split-plot design with mulching patterns served as the main plots and nitrogen rates served as the subplots. We compared four different mulching patterns with traditional plat planting (no mulching) as the control (M0). The mulching patterns included "W" ridge covered with common plastic film+ intredune covered with straw (M4), common ridge covered with common plastic film+ intredune covered with straw (M3), double ridges covered with common plastic film+ intredune covered with straw (M2), and the traditional plat planting covered with straw (M1). We used pure nitrogen as base fertilizer applied 180 (F4),135 (F3),90 (F2),45 (Fl) and 0 (F0) kg·hm-2, respectively. The objective of this field experiment was to explore the effects of mulching patterns and nitrogen rates on soil water, soil temperature and eco-physiology of broomcorn millet in the dryland of Loess Plateau. The results showed as follows:(1) Mulching could significantly improve the soil water and temperature conditions in broomcorn millet farmland, among them, the soil water retention effect represented M4>M3 >M2>M1, and the warming effect of plastic film mulching and cooling temperature effect of straw mulching were obvious. Nitrogen fertilizer could significantly reduce the soil water content and storage of broomcorn millet farmland, and when nitrogen applied more than 135 kg·hm-2, the soil water content and storage began to increase. Nitrogen fertilizer had no significant effect on the soil temperature at early stage of broomcorn millet. In addition, the soil water content and storage were higher at seedling and maturity stage, and lower at sowing and heading stage of broomcorn millet.(2) Mulching and nitrogen fertilizer could significantly increase top-three leaf chlorophyll content, net photosynthetic rate, stomatal conductance and transpiration rate, and decrease intercellular CO2 concentration during the stage from flowering to maturity in broomcorn millet. The photosynthetic improvement effect of mulching represented M4>M3 >M2>M1, and nitrogen improvement effect was F4>F3>F2>F1. In addition, the top-three leaf photosynthetic characteristics had no significant difference in broomcoro millet between years. At the stage from flowering to maturity of broomcorn millet, the top-three leaf chlorophyll content and stomatal conductance presented continuous reduction, net photosynthetic and transpiration rate exited synchronization relationship in the change with the raw of decline-slightly rise-sharply drop, and intercellular CO2 concentration constantly increase. During different periods of broomcorn millet, the top-three leaf chlorophyll content, net photosynthetic rate, stomatal conductance and transpiration rate represented flag leaf> top second leaf>top third leaf, and the intercellular CO2 concentration with top third leaf> top second leaf>flag leaf.(3) Mulching and nitrogen fertilizer could significantly increase top-three leaf soluble protein content, SOD activity and CAT activity, and decrease POD activity, MDA content and O2- content during the stage from flowering to maturity of broomcorn millet. The mulching aging delay effect presented M4>M3>M2>M1, and nitrogen aging delay effect was F4> F3>F2>F1. In addition, the top-three leaf aging characteristics had no significant difference in broomcorn millet between years. At the stage from flowering to maturity of broomcorn millet, the top-three leaf soluble protein content, SOD activity, POD activity and CAT activity represented continuous reduction, otherwise, the MDA content and O2-. content constantly increase. During different periods of broomcorn millet, the top-three leaf soluble protein content, SOD activity and CAT activity presented flag leaf>top second leaf>top third leaf, and POD activity, MDA content and O2-. content were top third leaf>top second leaf>flag leaf.(4) Mulching and nitrogen fertilizer could significantly improve the plant height, stem diameter and leaf area per plant at the whole period of broomcorn millet, among them, the mulching and nitrogen increasing effect presented M4>M3>M2>M1 and F4>F3>F2> Fl, respectively. In addition, the plant height, stem diameter and leaf area per plant increased before flowering, and stabilized after flowering of broomcorn millet.(5) Mulching and nitrogen fertilizer could significantly improve dry matter accumulation at the flowering and maturity stage of broomcorn millet, with M4>M3>M2>M1 and F4> F3>F2>F1, respectively. At the maturity stage of broomcorn millet, the dry matter allocation amount in different organs presented grain>stem + sheath>leaf>glume + spike axis. Mulching could significantly increase dry matter allocation amount in different organs, with M4>M3>M2>M1. The nitrogen fertilizer could significantly increase dry matter allocation amount in stem + sheath, leaf and glume + spike axis with F4>F3>F2>F1, and dry matter allocation amount in grain with F3>F4>F2>F1. In addition, the mulching and nitrogen fertilizer significantly reduced pre-flowering reserves translocation and contribution to grain, and increased post-flowering assimilates allocation and contribution to grain, and the treatment M4 and F3 indicated the most significant effects.(6) With the increase of nitrogen application rate, the grain total protein and protein components content increased in broomcorn millet, the proportion of other protein, albumin and globulin in grain total protein decreased, and the proportion of prolamin and glutelin in grain total protein increased, and the ratio of glutelin/prolamin also increased. In addition, the mulching and year had no significant effects on grain protein components content of broomcorn millet.(7) Mulching could significantly improve broomcorn millet grain yield, thousand grain mass, panicle length, panicle grain number and WUE, meanwhile reduce water consumption, and regulating effects presented M4>M3>M2>M1. Nitrogen fertilizer could significantly increase broomcorn millet grain yield, thousand grain mass, panicle length, panicle grain number, water consumption and WUE, and with the increase of nitrogen rate, the broomcorn millet grain yield, thousand grain mass, water consumption and WUE increased at first and then declined, and panicle length and panicle grain number constantly increased. In addition, optimum nitrogen application rate was between 135 and 145 kg·hm-2 in the broomcorn millet production in the dryland of Loess Plateau.Therefore, the water-saving fertilization technology of drought resistance and high yield in broomcorn millet, dual mulching for harvesting rainwater system M4 binding nitrogen rate 135～145 kg·hm-2, was recommended as an efficient farming technique and had an important application prospect in the agricultural production in the dryland of Loess Plateau. |
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