Seasonal patterns of soil moisture

Figure.5b showed the average soil moisture of three points 0, 25, and 50 cm from the lateral pipes and two profiles 0–20, 20–40 cm for two years 2007 and 2008 under different nitrogen application amount. All average soil moisture from 0 to 40 cm depth in whole growth period were maintained at above 50 available soil moisture except SDI N 75 under SDI and DI irrigation method.

3.2. Seasonal patterns of soil moisture

A. 2007 0-20cm 0.0 0.1 0.2 0.3 0.4 30 M ay 14 Jun 29 Jun 14 Jul 29 Jul 13 A ug 28 A ug 12 S ep S o il w ate r c o n te n t c m 3 c m 3 40 80 120 160 Ir rig atio n , r ain fa ll m m R I FC SDI N150 DI N150 WP B. 2007 20-40cm 0.0 0.1 0.2 0.3 0.4 30 M ay 14 Jun 29 Jun 14 Jul 29 Jul 13 A ug 28 A ug 12 S ep S o il w ate r c o n te n t cm 3 c m 3 40 80 120 160 Ir rig atio n , r ain fa ll m m R I FC SDI N150 DI N150 WP C. 2007 40-60cm 0.0 0.1 0.2 0.3 0.4 30 M ay 14 Jun 29 Jun 14 Jul 29 Jul 13 A ug 28 A ug 12 S ep S o il w at er c o n te n t c m 3 c m 3 40 80 120 160 Irri g at io n , ra in fa ll m m R I FC SDI N150 DI N150 WP D. 2008 0-20cm 0.0 0.1 0.2 0.3 0.4 2 Ju n 17 J un 2 Jul 17 J u l 1 A ug 16 A ug 31 A ug 15 S ep S o il w ate r c o n te n t c m 3 c m 3 40 80 120 160 Ir rig atio n , r ai n fa ll m m R I FC SDI N150 DI N150 WP Figure 5 . Soil mois ture at different layers a. Soil moistu re in 0-20, 20 -40, 40 -60 cm depth und er N 150 . E . 200 8 2 0- 40c m 0. 0. 1 0. 2 0. 3 0. 4 2Jun 17Jun 2Jul 17Jul 1Aug 16Aug 31Aug 15Sep Soil water content cm 3 cm 3 40 80 12 16 Irrigation, rainfall mm R I FC SD I N 1 5 D I N 150 WP F . 2 008 40- 60cm 0.0 0.1 0.2 0.3 0.4 2Jun 17Jun 2Jul 17Jul 1Aug 16Aug 31Aug 15Sep Soil water content cm 3 cm 3 40 80 120 160 Irrigation, rainfall mm R I FC SD I N 1 5 DI N 1 5 WP A . 200 7 S D I 0. 0. 1 0. 2 0. 3 0. 4 30May 14Jun 29Jun 14Jul 29Jul 13Aug 28Aug 12Sep Soil water content cm 3 cm 3 40 80 12 16 Irrigation, rainfall mm R I FC WP N0 N7 5 N1 50 N3 00 B . 20 07 D I 0.0 0.1 0.2 0.3 0.4 30May 14Jun 29Jun 14Jul 29Jul 13Aug 28Aug 12Sep Soil water content cm 3 cm 3 40 80 12 16 Irrigation, rainfall mm R I FC WP N0 N7 5 N150 N300 b. Average soil moisture of 0-40 cm depth under different nitrogen treatment. 3.3. Root distribution Table 5. Root length density RLD of bell pepper as influenced by irrigation method and N application levels Treatment RLDcmcm 3 2007 2008 Nitrogen N 0.42c 0.18d N 75 0.51b 0.30b N 150 0.61a 0.33a N 300 0.39c 0.22c Irrigation SDI 0.51a 0.27a DI 0.45b 0.24b Average of two irrigation methods. Average of four different nitrogen levels. Table 5 shows a significant difference in RLD between SDI and DI and among the different nitrogen levels. RLD obviously increased with increasing nitrogen levels until the nitrogen level reached 150 kgha in both years, and then it sharply decreased. The effect of irrigation methods on RLD was apparent; the RLD of SDI was obviously higher than that of DI. At the same fertilization level, the root length and percentage of root length in each layer to total root length decreased with soil depths Table 6. The percentages of root length at 30-40 cm soil depth to total root length under DI and SDI were 1.25 DI N 150 and 2.81 SDI N 150 , respectively, indicating that there were almost no bell pepper roots below 40 cm soil depth. Root lengths under SDI N , SDI N 75 , SDI N 150 , and SDI N 300 were 1.06, 1.06, 1.46, and 1.07 times longer than those under DI N , DI N 75 , DI N 150 , and DI N 300 , respectively. The percentage of root length below 10 cm soil depth under SDI N 150 was higher than that under DI N 150 by 7. Hence, SDI does not C. 2008 SDI 0.0 0.1 0.2 0.3 0.4 2 Jun 17 J u n 2 Ju l 17 J ul 1 A ug 16 A u g 31 A u g 15 S ep S o il w ate r c o n te n t c m 3 c m 3 40 80 120 160 Ir rig ati o n , ra in fa ll m m R I FC WP N0 N75 N150 N300 D. 2008 DI 0.0 0.1 0.2 0.3 0.4 2 Jun 17 J u n 2 Jul 17 J u l 1 A ug 16 A u g 31 A u g 15 S ep S o il w ate r co n te n t c m 3 c m 3 40 80 120 160 Ir rig atio n , r ain fa ll m m R I FC WP N0 N75 N150 N300 only promote root growth but also results in deeper root development. Table 6. Bell pepper root length at different soil depths Depth cm 0–10 10–20 20–30 30–40 0–40 DI N Root lengthcm 7431 3772 719 431 12354 Proportion 53.47 27.14 5.18 3.10 100 SDI N Root lengthcm 6038 4976 1370 750 13135 Proportion 45.97 37.88 10.43 5.71 100 DI N 75 Root lengthcm 8263 6917 1922 937 18038 Proportion 45.81 38.34 10.65 5.19 100 SDI N 75 Root lengthcm 6923 8017 3035 1255 19231 Proportion 36.00 41.69 15.78 6.53 100 DI N 150 Root lengthcm 11582 4588 1089 219 17479 Proportion 66.26 26.25 6.23 1.25 100 SDI N 150 Root lengthcm 15235 7353 2319 719 25625 Proportion 59.45 28.69 9.05 2.81 100 DI N 300 Root lengthcm 8555 4076 919 827 14377 Proportion 59.51 28.35 6.39 5.75 100 SDI N 300 Root lengthcm 7199 6419 951 820 15390 Proportion 46.78 41.71 6.18 5.33 100 Under the same irrigation methods, the impact of different nitrogen levels on RLD at harvest is shown in Fig.6. At 0–10 cm soil depth, RLD gradually increased with increasing nitrogen levels. However, at 10–20 cm soil depth, RLD declined sharply when the nitrogen level exceeded 150 kgha. These findings imply that too much nitrogen application inhibits root growth in deeper soil layers. Figure.6 RLD distribution during the 2007 growing season in all treatments 3.4. NO 3 - -N distribution in soils Figure.7 shows NO 3 - -N concentrations in soil 2 d before fertilization Aug 14, 2 d after fertilization Aug 18, and 22 d after fertilization Sep 7. Before fertilization, there was no significant difference in NO 3 - -N distribution between SDI and DI. However, 2 d after fertilization, NO 3 - -N concentrations under SDI treatment were distributed with a parabolic curve; the maximum value 14.2 mgkg was found at 20–40 cm soil depth. In contrast, NO 3 - -N concentrations under DI treatment declined with increasing soil depth, and a maximum concentration 15.7 mgkg was obtained at the top soil 0–20 cm. Furthermore, 22 d after the fertilization, NO 3 - -N gradually moved downward due to water movement, crop growth, and root activities. The maximum NO 3 - -N concentration 22 d after fertilization under SDI and DI occurred at 40–60 cm and 60–80 cm, respectively. SDI 10 20 30 0.0 0.2 0.4 0.6 0.8 1.0 RLD cm•cm -3 D ept h cm N0 N75 N150 N300 DI 10 20 30 0.0 0.2 0.4 0.6 0.8 1.0 RLD cm•cm -3 D ept h cm N0 N75 N150 N300 Figure 7. Vertical distribution of NO 3 - -N concentration in soil profiles As mentioned above, bell pepper roots were concentrated at 0–40 cm soil depth. Nitrogen leaching below 40 cm, which was hardly useful to the plants, was of residual value. The maximum residual NO 3 - -N concentration at 40-60 cm under SDI 8.4 mgkg was far lower than that under DI treatment 13.8 mgkg at 60–80 cm. Residual NO 3 - -N concentrations in soil profiles increased with increasing levels of nitrogen fertilizers Fig. 8, but the residual of N 150 was only slightly higher than N 75 . The NO 3 - -N residual concentration for N 300 treatment was sharply higher than that for N 150 treatment 22 d after fertilization. This tend was found in all nitrogen treatments. The data above show that SDI promoted the development of bell pepper roots and favored the establishment of intensive root layers, which can prevent nitrate leaching. At nitrogen level lower than 150 kgha, fertigation produced lesser residues. SDI N 150 20 40 60 80 100 10 20 30 40 N0 3 - -N distribution mg.kg -1 dept h cm 14-Aug 18-Aug 7-Sep DI N 150 20 40 60 80 100 10 20 30 40 N0 3 - -N distribution mg.kg -1 d ept h cm 14-Aug 18-Aug 7-Sep 18-Aug-2007 SDI 20 40 60 80 100 10 20 30 40 NO 3 - -N distribution mg.kg -1 de p th cm N75 N150 N300 18-Aug-2007 DI 20 40 60 80 100 10 20 30 40 NO 3 - -N distribution mg.kg -1 de pt h cm N75 N150 N300 Figure 8. Vertical distribution of NO 3 - -N as influenced by different nitrogen levels 3.5. ET c Bell pepper plants were transplanted at May 20 in 2007 and May 21 in 2008. The growth seasons last 118 d and 115 d separately in 2007 and 2008. Bell pepper ET c was calculated by formula 1. D in formula 1, the amounts of drainage water collected from the lysimeter are shown in Table.7. Table.8 shows the cumulative water consumption of bell pepper and ET calculated by Penman-Monteith’s formula during the two growing seasons. The ET c and ET of all treatments in 2008 were lower than those in 2007 due to the lower monthly average temperature in 2008. as compared with 2007. A very low temperature 2.4 °C in May 30, 2008 inhibited seedling establishment. Table 7. Drainage water amounts mm a. 2007 SDI N SDI N 75 SDI N 150 SDI N 300 DI N DI N 75 DI N 150 DI N 300 16-Jul 5.2 2.4 20-Jul 5.6 4.9 24-Jul 6.0 2.9 27-Jul 8.5 6.9 5-Aug 5.7 7-Aug 3.9 13-Aug 4.9 5.3 16-Aug 5.0 17-Aug 13.9 5.9 21-Aug 11.4 5.7 5.5 25-Aug 11.8 5.6 3.5 26-Aug 8.2 6.5 14.7 7.8 22.7 10.7 10.8 2-Sep 2.1 5-Sep 3.4 9-Sep 1.8 10-Sep 11.5 6.3 8.3 Total 105 47.5 19.6 11.7 22.7 28 10.8 7-Sep-2007 SDI 20 40 60 80 100 10 20 30 40 NO 3 - -N distribution mg.kg -1 dept h cm N0 N75 N150 N300 7-Sep-2007 DI 20 40 60 80 100 10 20 30 40 NO 3 - -N distribution mg.kg -1 de pt h cm N0 N75 N150 N300 b. 2008 SDI N SDI N 75 SDI N 150 SDI N 300 DI N DI N 75 DI N 150 DI N 300 9-Jul 3.6 16-Jul 9.8 5.3 5.4 7.5 20-Jul 16.7 15.3 12.2 18.2 3.1 24-Jul 19.2 12.3 10.6 16.6 2.2 2.4 25-Jul 2.3 2.1 2.6 1.2 29-Jul 2.9 5.3 2.7 5.4 4.6 5.4 5.4 5-Aug 10 8.4 3.5 7.2 9 7.0 10-Aug 3.5 7.5 3.8 8.5 2.7 Total 62.1 33.2 31.8 42.7 25 25.4 2.6 9.3 Table 8. Cumulative water consumption under different irrigation and fertilization practices ET mm ET c mm N N 75 N 150 N 300 2007 508 DI 407 426 451 404 SDI 301 405 438 432 2008 406 DI 362 387 382 382 SDI 334 357 377 359 The maximum and minimum water consumption were recorded for DI N 150 treatment 451 mm and SDI N treatment 301 mm, respectively, in 2007. In 2008, the maximum water consumption was recorded for DI N 75 387 mm, followed by DI N 150 and DI N 300 382 mm. The minimum value was at 334 mm for SDI N . Except for N 300 treatment in 2007, all cumulative water consumptions under SDI were lower than under DI. 2007 1 2 3 4 5 6 7 seedling stage blossom and fruit set period full bearing period the late stages of development dai ly w at er cons u m pt ion m m ·d -1 DI N150 SDI N150 Figure 9. Daily averaged water consumption at different growth stages Daily average water consumptions at different growth stage under different irrigation techniques N 150 treatment are shown in Fig.9. During the seedling establishment period, the DI method resulted in higher daily averaged water consumption compared with SDI because of higher evaporation under DI. After entering the blossom and fruit- set period, the daily average water consumption under SDI became higher than that under DI. This result may be attributed to faster root growth under SDI than under DI. At full bearing period, the plants grew vigorously, leading water consumption to reach its maximum. Water consumption under SDI was lower than that under DI, contributing to low plant height and leaf area Fig. 10. However, daily average water consumption under DI was slightly lower than that under SDI at the late crop growth stages. 2008 1 2 3 4 5 6 7 seedling stage blossom and fruit set period full bearing period the late stages of development d ai ly w at er co ns u m pt io n m m ·d -1 DI N150 SDI N150 10 20 30 40 50 19Jun 1Jul 13Jul 25Jul 6Aug 18Aug 30Aug 11Sep Hei g h t c m SDI N0 SDI N75 SDI N150 SDI N300 DI N0 DI N75 DI N150 DI N300 Figue 10. Plant height and LAI for different treatments 2007 There was a polynomial correlation between crop water consumption and nitrogen levels Fig.11. ET c increased with increasing nitrogen levels, reaching a maximum value at 150 kgha nitrogen level. Thereafter, ET c again declined. Nitrogen became excessive after 150 kgha and too much nitrogen restricts bell pepper growth leading to lower ET c. Figure 11. Relationship between ET c and nitrogen levels 2 4 6 8 10 12 19Jun 1Jul 13Jul 25Jul 6Aug 18Aug 30Aug 11Sep LA I SDI N0 SDI N75 SDI N150 SDI N300 DI N0 DI N75 DI N150 DI N300 2007 y SDI = -0.0035x 2 + 1.4546x + 305.09 R 2 = 0.9838 y DI = -0.0018x 2 + 0.5418x + 403.82 R 2 = 0.9204 250 300 350 400 450 500 50 100 150 200 250 300 Nitrogen applied amount kg N·ha -1 ET c m m DI SDI 2008 y SDI = -0.0013x 2 + 0.4679x + 332.57 R 2 = 0.9743 y DI = -0.0007x 2 + 0.251x + 364.92 R 2 = 0.7637 300 325 350 375 400 50 100 150 200 250 300 Nitrogen applied amount kg N·ha -1 ET c mm DI SDI Table 9. Calculated k c at each growth stage a. SDI N 150 , 2007 ET ET c Calculated k c k c recommended by FAO- Seedling establishment 167 115 0.69 0.6 Blossom and fruit-set period 120 101 0.84 1.05 Full bearing period 160 191 1.19 1.05 Late crop growth stages 60 44 0.74 0.9 Whole growing season 508 451 0.89 b. SDI N 150 , 2008 ET ET c Calculated k c k c recommended by FAO- Seedling establishment 115 76 0.66 0.6 Blossom and fruit-set period 107 87 0.82 1.05 Full bearing period 115 149 1.30 1.05 Late crop growth stages 69 65 0.93 0.9 Whole growing season 406 377 0.93 Crop coefficient k c for bell pepper at different growth stages for the experimental site under SDI N 150 is shown in Table 9. At the seedling establishment and full bearing periods, k c values were higher than the values recommended by FAO-56. On the contrary, k c at the blossom and fruit-set period was higher than that recommended by FAO-56. Meanwhile, k c at the late crop growth stages was not stable.

3.5. Yield and water use efficiency