Effecct Of Seeding Rate And Root Pruning On Grain Yield And Water Use Efflciency In Winter Wheat On Loess Plateau

As a major world crop, winter wheat has shown increased yields following advancesin breeding and crop management. On the semi-arid Loess Plateau of China, water stress isone of the major limiting factors of yield for winter wheat. The improvements in grainyield and water use efficiency (WUE) are two equally important goals in arid or semi-aridareas. ChangWu 135, which developed for the semi-arid dryland agriculture area of theLoess Plateau, was studied in the experiments. Pot experiments and field experiments wereconducted to assess whether seeding density in winter wheat affects grain yield and wateruse efficiency when combined with root pruning by changes in the accumulation,remobilization of photosynthate and water consumption.Two experiments were conducted in our research:Experiment 1:(1) Pot experiment and field experiment were conducted in 2007/08. Pot experimentcomprised four treatments: (1) LN, low density (12 seedlings to a pot, 8 cm in diameter×50 cm high) and no root pruning; (2) LP, low density with root pruning; (3) HN, highdensity (15 seedlings to a pot, 25% higher than low density) and no root pruning; and (4)HP, high density with root pruning. Two water regimes were employed from stemelongation: (i) plants maintained at 85% field capacity, and (ii) plants maintained at 55%field capacity by regular watering. At stem elongation roots were pruned 40⁴2% on 2March. And roots were cut back to keep their length to 13 cm and to limit their lateralspread to 3 cm from the plant.(2) Field experiment comprised four treatments: (1) LN: plants at low density (225 seedsm^-2, the recommended density in the region), roots not pruned; (2) LP: plants at lowdensity, roots pruned; (3) HN: plants at high density (280 seeds m^-2, 25% higher than lowdensity), roots not pruned; and (4) HP: plants at high density, roots pruned. At stemelongation roots were pruned by 40⁴2% on 15 March. And roots were cut back to keep their length to 13 cm and to limit their lateral spread to 3 cm from the plant.Experiment 2: Field experiments conducted in 2007/08 and 2008/09 comprised. Theseeding rates were: SR1 (225 seeds m^-2 the optimal seeding rate for the region),; SR2, 280seeds m^-2; and SR3, 340 seeds m^-2. Two root pruning treatments were: W (roots pruned on15 November just at the beginning of over-wintering period) and S (root pruned on 15March at the beginning of the spring-growth stage); un-pruned plants (CK) served as thecontrol. Roots were pruned by 40⁴2%.The main results are as follows:1. The effects of grain yield by seeding rate and root pruning. In the pot study, the yieldreduction with water shortage. Grain yield increased significant with seeding rateincreased under the well watered condition. Normal seeding rate had no effect on grainyield, while higher seeding rate increased grain yield significantly when root pruning.Field Experiment observed that grain yield decreased with the seeding rate increased insevere drought years. However, the reverse result was observed favorable weather.Similar results found in pot experiment.2. The effects of water use efficiency by seeding rate and root pruning. In pot experiment,availability of water significantly increased overall water use as did increasing theplanting density (P<0.01), but root pruning increased water use efficiency significantly.In experiment 2, root pruning in winter (W) primarily led to a significant decrease inwater use from winter to stem elongation stage. While root pruning in springsignificant reduced water use after stem elongation stage, used less soil water thanwinter pruned roots and the un-pruned controls, and had highest water use efficiency.3. The effect of root biomass by seeding rate and root pruning. In experiment 1,rootbiomass and R:S ratio significant increased with increasing seeding rate. The reservesresults found in root pruning treatment. In field experiment, root biomass in each layerof soil were higher at the higher planting density at anthesis, while root pruningsignificantly (P<0.05) reduced the root biomass in the upper 40 cm of soil, butincreased the root biomass and the proportion of root biomass in the 80-120 cm soillayer.4. The effect of population structure by seeding rate and root pruning. In experiment 2,higher seeding rates led to higher LAI. However in 2008 seeding rate had no significant effect on LAI. The total number of tillers (fertile tillers: those with a headand infertile tillers: those without a head) per unit area increased linearly with seedingrate whereas the number of tillers per plant decreased, and the spiker density did notaffect by seeding rate. Two root pruning treatments increased the values of LAI in bothseasons and decreased tiller density and the number of tillers per plant (P<0.05), buthad little effect on the number of fertile tillers (spikes).5. The effect of the exchange of gases by seeding rate and root pruning. Water shortageand increasing the planting density significantly decreased flag leaf photosynthesis andphotosynthetic activity, while root pruning significantly increased the photosyntheticcapacity of the flag leaf in pot experiment. In experiment 2, higher seeding ratesdecreased the rate of flag leaf photosynthesis (Pn) and photosynthetic activity,increased the rate of root respiration (Rr), leading to a significant decrease in rootefficiency (Pn : Rr). In contrast, leaf photosynthetic rate increased and root respirationrate decreased in the root pruning treatments, leading to a higher Pn : Rr ratio. Itindicated that the reducing of root biomass decreased the carbon consumed, leading tomore photosynthetic product was used to increase grain yield.6. The effect of seeding rate and root pruning on competition ability of winter wheat wasinvested using de Wit replacement series. In experiment 1, the relative yield ofunpruned plant was significantly higher than 1 while root pruning wheat was lowerthan 1 in mixture. The relative total yield of normal density was 1.06 when water wasplentiful, which was significant greater than 1, indicated that unpruned plant was asuperior competitor, the mixture of unpruned plant and root pruning in normal densitycould increase the grain yield significantly under the well watered condition.7. Nitrogen and phosphorus use efficiency were researched in field experiment. Thenitrogen and phosphorus in leaves decreased with the seeding rate increased. Two rootpruning treatments had higher nitrogen and phosphorus content in leaves than that ofunpruned treatment. It suggested that the higher photosynthetic rate of root prunedplant may associate with the higher nitrogen and phosphorus content in leaves.8. In experiment 2, both post-heading dry matter accumulation and translocationsignificantly increased with seeding rate. In W and S, post-heading dry matteraccumulation significant higher than unprunned plants. Post-heading dry matter accumulation was very important for increasing grain yield, it suggested that thegreater grain yield of root pruning plants may associate with the higher post-headingdry matter accumulation.In presednt study, increasing seeding rate and root pruning treatments can increasegrain yield and water use efficiency in average-rainfall years on the semi-arid LoessPlateau. The greater grain yield in higher seeding rate derived from higher spike densityand grain number per unit. While root pruning reduced the water consumption beforeanthesis, more soil water used for grain filling, and increased water use efficiency.Meanwhile, root pruning reduced the infertile tillers, improved the canopy structure,decreased the useless carbon consumed, and increased the post-heading dry matteraccumulation, and resulted in higher grain yield. However, the competition of soil water inwinter wheat increased due to increasing seeding rate and led to decreased grain yield insevere drought years. In conclusion, it is hopeful that improved grain yield and water useefficiency by increasing seeding rate and root pruning in arid or semi-arid areas.