Effects of planting density and sowing method on growth, development, yield and quality of peanut in saline alkali land

To study the effects of planting density and seeding method on agronomic trait, yield and quality of peanut and to determine optimal planting density and seeding method for peanut in saline soils, a peanut (Huayu 25, salt-tolerant cultivar) field plot experiment containing five single-seed planting density treatments and three double-seeds planting density treatments was conducted. Experiment 1 was the single-seed planting experiment containing 5 planting densities — 180 thousand hole·hm^-2 (M1), 196 thousand hole·hm^-2 (M2), 214 thousand hole·hm^-2 (M3), 235 thousand hole·hm^-2 (M4) and 260 thousand hole·hm^-2 (M5), respectively. Experiment 2 was the double-seed planting experiment, consisting of 3 planting densities — 116 thousand hole·hm^-2 (M6), 130 thousand hole·hm^-2 (M7) and 147 thousand hole·hm^-2 (M8). The results showed that soil salinity stress greatly inhibited the growth of peanut plant. Compared with peanut in non-saline soils, peanut stem and branch length reduced significantly, which were 25.6 cm and 29.0 cm, respectively. For single-seed planting in the density range of 196260 thousand hole·hm^-2, the height of stem and length of branch significantly reduced with increasing planting density before pod-filling stage. Before pod-swelling and after pod-filling stage, the numbers of primary and secondary branch of single-seed planting were higher than that of double-seed planting in the range of M2M4. The stem base length decreased with increasing density, but the difference was not significant. Changes in length and thickness of stem base mainly occurred before pod-setting stage, and the rate of stem elongation was faster than the rate of cross-sectional area increase. The length and thickness of stem base tended to stabilize at late growth stage. The period of rapid accumulation of photosynthetic products in the leaves, stems and petioles of peanut in saline soils was mainly at flowering, pegging and pod swelling stages. The maximum growth rate (V_m) of leaves was only half of that of stems and petioles. The rapid growth stage leaves was 5 days earlier than that of stems and petioles. Also the V_m time of leaves, stems and petioles under the single-seed planting lagged behind that under double-seed planting. Peanut shoot V_m characterized by “parabola type” changed with increasing planting density. The leaves, stems and petioles of V_m were largest under M4 treatment, which were 0.492 5 g per plant and 0.878 3 g per plant, respectively. The effect of planting density on the accumulation of photosynthetic products in peanut was more significant, but the distribution rate of each organ in each period was not significantly different. Peanut photosynthetic products in saline soils were roughly identical to those in non-saline soils. Photosynthetic products were in the stems and leaves at the early growth stage and a third of the photosynthetic products was at pods at pod to pod-filling stage. The effect of planting density on pod yield was significant under single-seed planting, but was not significant on kernel soluble sugar, protein, fat, and the ratio of oleic and linoleic acid. For the single-seed planting, the optimum density was 190235 thousand hole·hm^-2.