Effects Of Planting Density On Yield, Quality And Physiological Basis In Wheat Under Irrigated And Rainfed Conditions

A field experiment was carried out at experimental plot of Shandong Agricuture University in 2006-2007. The combination experiments including field plot experiment, irrigated conditions and planting density, using two wheat cultivars, PH01-35, JN17 with high gluten content and different spike type, to study the effects of planting density on yield, quality and physiological basis in wheat under irrigated and rainfed conditions. The main results were as follows.1. Effects of planting density on the yield and quality in grain under irrigated and rainfed conditionsUnder irrigated and rainfed conditions, increasing planting density improved the spike number of hectare, spikelets without grain setting, reduced the kernel number per spike, kernel weight per 1000 grains, spike length, spikelets with grain setting and plant height. Effects of planting density on the wheat yield was differed under different irrigation conditions, at rainfed condition, the wheat yield trend to increasing slightly with the increase of planting density, however, at irrigated condition, the wheat yield had great difference in treatments of planting density, the trend as following: 270plants/m2>360plants/m2>180plants/m2, but no significant correlation was founded between 270plants/m2 and 360plants/m2 treatments. Compared with irrigated plants, besides spikelets without grain setting, other indexs trend to reducing sharply subjected to soil water deficit.Increasing planting density and soil water deficit significantly decreased the grain weight. The grain weight had the same changes owing to the change of planting density under different irrigation conditions, simulation the process of grain filling in different treatments with Logistic Equation, and correlation analysis showed that it was mean grain filling rate and grain filling duration, but not other parameters declined the grain weight under different planting density and soil moisture.Effects of planting density on the grain quality were differed under different irrigation conditions. At rainfed condition, it showed that the water absorption rate, wet gluten content, dough stability time, dough development time and sedimentation trend to decreasing with the increase of planting density, however, which as following: 270plants/m2>360plants/m2>180plants /m2 at irrigated condition, no significant correlation was founded between water absorption rate, ough development time and planting density. Compared with irrigated plants, wet gluten content, dough stability time and sedimentation trend to reducing subjected to soil water deficit.2. Effects of planting density on the contents of the starch and starch components in grain under irrigated and rainfed conditionsUnder irrigated and rainfed conditions, the contents of total starch and amylopectin had great difference in treatments of planting density, the trend as following: 270plants/m2>360plants/m2>180plants/m2, but the amylose content of grains decreased siginificantly with the increase of planting density. Then, the ratio of amylose and amylopectin was reduced sharply. Compared with irrigated plants, the amylose content, amylose/amylopectin ratio reduced significantly subjected to soil water deficit, however, the content of total starch increased slightly.At maturity, wheat contained two types of starch granules: smaller B-type granules(<9.8μm) and large A-type granules(>9.8μm). The diameter of starch granules changed in the range of 0.37~52.6μm. Volume distribution of starch granules showed the typical two populations with peak values in 5μm and 25μm, respectively. The number distribution of starch granules exhibited a single peak curve with peak at 1μm. The number of B-type starch granule comprised over 99% of the total starch granule numbers, indicating that the number of starch granules was mainly small starch granules. Similar to the volume distribution, the surface area distribution also showed double peak curves with peak at 2.8μm and 23μm. The B-type starch granules comprised about 80%, and A-type starch granules contributed about 20% of the total surface area.Effects of planting density and irrigation patterns on the starch granule size distribution of grains was different. Under irrigated and rainfed conditions, The volume and surface area percent of A-type starch granules reduced with the increase of planting density, however, the volume and surface area percent of B-type starch granules trended to rising. No significant correlation was founded between the numbers percent of A-type, B-type starch granules and the changes of planting density. Compared with irrigated plants, the volume and surface area percent of B-type starch granules increased subjected to soil water deficit, however, the volume and surface area percent of A-type starch granules trended to decreasing, and no significant correlation was founded between the numbers percent of A-type, B-type starch granules and soil moisture.3. Effect of planting density on the contents of protein and protein components in grain under irrigated and rainfed conditionsEffects of planting density on the contents of protein and protein components in Grains were differed under different irrigations. At rainfed condition, the contents of protein, globulin, glutenin, GMP and HMW-GS decreased with the increase of planting density, the correlation of the GMP, HMW-GS with planting density were closer than others. The planting density impact significantly both glutenin and gliadin contents at early period of grain filling, but this response was weakened stepwise afterward. Till the maturity there was no significant difference in albumin and globulin contents. No significant correlation was founded between glutenin/gliadin ratio and the changes of planting density.At irrigated condition, increasing planting density from 180/m2 to 270 plants/m2 could significantly increase the contents of protein, globulin, glutenin, GMP and HMW-GS in the grains, and when planting density reached 360 plants/m2, the contents of protein, globulin, glutenin, GMP and HMW-GS in the grains were decreased significantly, but no significant correlation was founded between glutenin, gliadin contents, glutenin/gliadin ratio and the changes of planting density. Compared with irrigated plants, the contents of protein, glutenin, gliadin, globulin, glutenin, GMP and HMW-GS in the grains tended to reducing subjected to soil water deficit, and no significant correlation was founded between glutenin/gliadin ratio and soil moisture.4. Effects of planting density on Physiological characteristics of wheat under irrigated and rainfed conditions4.1 Photosynthesis characteristics in flag leafUnder irrigated and rainfed conditions, the net photosynthetic rate (Pn), stomatal gas conductance (Gs) and mesophyll gas conductance (Gm) in flag leaf tended to reducing with the increase of planting density. Compared with irrigated plants, soil water deficit also decreased significantly Pn, Gs and Gm in flag leaf, the correlation of the Pn, Gs and Gm in flag leaf with the irrigation was closer than planting density.4.2 The change of chlorophyll content and chlorophyll fluorescence parameters in flag leafUnder irrigated and rainfed conditions, the content of chlorophyll a, chlorophyllb, chlorophyll a+b in flag leaf tended to reducing with the increase of planting density. Increasing planting density reduced the chlorophyll fluorescense dynamics parameters, Fv/Fm,φPSⅡand increased Fo, NPQ , the Fo reduced sharply at late filling stage. Compared with irrigated plants, soil water deficit reduced the content of chlorophyll b,chlorophylla+b, also reduced smartly chlorophyll fluorescensedynamics parameters, Fv/Fm,φPSⅡ,increased Fo, NPQ, effect of soil water deficit on Chlorophyll b was differed in two wheat cultivars.4.3 The change of water saturation deficit and water potential in flag leafThe WSD of flag leaf tended to rising with grain filling stage, rose slightly within 0 and14 days after anthesis, rose sharply within 21days and 28 days after anthesis. Under irrigated and rainfed conditions, the WSD of flag leaf tended to rising with increasing planting density. Compared with irrigated plants, reduced level of WSD of flag leaf subjected to soil water deficit. The results also showed that the change ofΨt could be outlined by"U"letter curve, the values ofΨt in flag leaf is higher in forenoon than that in afterrnoon. At the same irrigation amount, the value ofΨt in flag leaf tended to reducing with the increase of planting density, but no significant correlation was founded between planting density and the thereshold values ofΨt in flag leaf. Compared with irrigated plants, the values ofΨt in flag leaf tended to reducing, the thereshold values ofΨt in flag leaf were advanced subjected to soil water deficit.5. Effects of planting density on dry matter accumulation under irrigated and rainfed conditionsUnder irrigated and rainfed conditions, the accumulations of dry matter in flag leaf, other leaves, sheath, stem, spike axis, total matter trend to reducing with the planting density increased, the percent of other leaves, sheath, stem, the total of spike axis and glume in total dry matter accumulation trend to increasing, however, the percent of flag leaf, kernel in total dry matter accumulation trend to reducing significantly. Compared with irrigated plants, the accumulation of dry matter in skenel trend to reducing subjected to soil water deficit, the percent of skenel in total dry matter accumulation also reduced. It showed that soil water deficit and increasing planting density went against accumulation and transport of dry matter in procreation organs.