早播及耕作措施对黄土高原半干旱区春小麦土壤氮磷元素的影响

doi:10.13866/j.azr.2021.05.18

摘要/Abstract

摘要：

为探讨早播及耕作措施对农田生态系统土壤氮磷元素影响规律,对黄土高原半干旱区早播、正常播下不同耕作措施[传统耕作（T）、传统耕作+秸秆还田（TS）、免耕（NT）、免耕+秸秆覆盖（NTS）]春小麦（Triticum aestivum）生育期0~40 cm土壤进行分析,以正常播种传统耕作春小麦为对照,研究早播及耕作措施对春小麦土壤氮磷元素的影响。结果表明：（1）不同处理下春小麦土壤N素（TN、$NO_3^--N$、$NH_4^+-N$）、P素（TP）含量均具有表聚性特征,其土壤N:P均值（1.713）低于全国平均值（5.2）,同时其变异水平系数处于26.99%~77.28%,属中等变异水平;（2）全生育期0~40 cm土层,早播春小麦土壤TN、$NH_4^+-N$含量及N:P均值显著低于正常播23.1%~32.5%,不利于土壤TN、$NH_4^+-N$含量积累,而$NO_3^--N$含量及$NO_3^--N$均值显著高于正常播30.5%、41.5%,有助于土壤$NO_3^--N$含量的固存,同时早播处理下土壤TP含量整体高于正常播处理;（3）秸秆覆盖措施（NTS、TS）下土壤TN、TP含量高于NT、T,但速效氮（$NO_3^--N$、$NH_4^+-N$）养分含量表现相反;（4）不同处理下春小麦土壤TP含量在生育期间趋于稳定,而N素含量在分蘖期及开花期变化较显著。因此,选择适宜播种时间及耕作管理措施有助于提高该区作物土壤N、P元素的积累转化效率,加快发展黄土高原半干旱区农田生态系统恢复进程。

关键词: 黄土高原半干旱区, 早播, 耕作措施, 春小麦, 土壤氮磷

Abstract:

To study the effects of early sowing and tillage measures on soil nitrogen and phosphorus in a farmland ecosystem, 0-40 cm of soil supporting spring wheat (Triticum aestivum) in the semi-arid region of the Loess Plateau was collected and analyzed. Under early sowing and normal sowing conditions, the different tillage measures were as follows: traditional tillage (T), traditional tillage + straw returning (TS), no tillage (NT), and no tillage + straw mulching (NTS). Results were as follows. (1) Under different treatments, the contents of N (TN, $NO_3^--N$, and $NH_4^+-N$) and P (TP) in spring wheat-related soil had the characteristics of surface aggregation. The average value of soil N:P (1.713) was lower than the national average value (5.2) and the coefficient of variation was 26.99%-77.28%, which belonged to the medium variation level. (2) In the 0-40 cm soil layer, the TN,$NH_4^+-N$, and N:P levels of early sowing spring wheat were significantly lower than the levels found with normal sowing (i.e., by 23.1%-32.5%), which was not conducive to the accumulation of TN and $NH_4^+-N$, whereas $NO_3^--N$ and $NO_3^--N$:N levels were significantly higher in early sowing spring wheat than the levels achieved with normal sowing (i.e., by 30.5% and 41.5%, respectively), which was conducive to the retention of $NO_3^--N$ in the soil. (3) The contents of TN and TP under straw mulching conditions (NTS and TS) were higher than those under NT and T, but the contents of available nitrogen ($NO_3^--N$ and $NH_4^+-N$) showed the opposite trend. (4) Under different treatments, the contents of TP in the soil tended to be stable during the growth period, whereas the contents of N changed significantly at the tillering and flowering stages. Therefore, selecting suitable sowing times and tillage management measures will help to improve the accumulation and transformation efficiency of N and P elements in crop soil and will accelerate the restoration process of farmland ecosystems in the semi-arid area of the Loess Plateau.

Key words: semiarid region of Loess Plateau, early sowing, tillage measures, spring wheat, soil nitrogen and phosphorus

刘帅楠,李广,宋良翠,袁建钰,谢明君,魏星星. 早播及耕作措施对黄土高原半干旱区春小麦土壤氮磷元素的影响[J]. 干旱区研究, 2021, 38(5): 1367-1375.

LIU Shuainan,LI Guang,SONG Liangcui,YUAN Jianyu,XIE Mingjun,WEI Xingxing. Effects of early sowing and tillage measures on nitrogen and phosphorus in the soil supporting spring wheat in the semi-arid area of the Loess Plateau[J]. Arid Zone Research, 2021, 38(5): 1367-1375.

图/表 7

表1

图1

表2

图2

图3

表3

春小麦不同处理下全生育期0~40 cm土壤$NO_3^--N$、$NO_4^+-N$元素特征"

处理	$NO_3^--N$			$N O 4 +$ -N			$NO_3^--N$∶N			$NH_4^+-N$∶N
处理	标准差	均值/（mg·kg^-1）	CV/%	标准差	均值/（mg·kg^-1）	CV/%	标准差	均值	CV/%	标准差	均值	CV/%
T	1.671	2.811AB	59.45	1.049	2.446A	42.89	0.010	0.018BC	56.74	0.008	0.016A	49.56
TS	0.980	2.242BC	43.70	0.861	2.165AB	39.77	0.006	0.012D	52.83	0.004	0.011BC	39.37
NT	1.548	2.341BC	66.14	0.979	2.276AB	43.02	0.008	0.013CD	59.70	0.004	0.012B	33.06
NTS	0.806	1.822C	44.26	0.915	2.247AB	40.73	0.004	0.009D	48.88	0.003	0.010BC	29.52
ET	2.009	3.453A	58.18	1.169	1.759BC	66.48	0.014	0.026A	53.59	0.008	0.013AB	63.56
ETS	1.542	3.283A	46.98	1.040	1.495C	69.54	0.010	0.021AB	46.10	0.006	0.010BC	65.88
ENT	2.647	3.425A	77.28	1.121	1.613C	69.48	0.016	0.022AB	71.94	0.008	0.011BC	73.15
ENTS	1.659	3.047AB	54.44	0.947	1.311C	72.26	0.011	0.019BC	58.17	0.006	0.008C	72.41

表3

表4

参考文献 40

[1]	张凯, 李巧珍, 王润元, 等. 播期对春小麦生长发育及产量的影响[J]. 生态学杂志, 2012, 31(2): 324-331.
	[ Zhang Kai, Li Qiaozhen, Wang Runyuan, et al. Effects of sowing date on the growth and yield of spring wheat[J]. Chinese Journal of Ecology, 2012, 31(2): 324-331. ]
[2]	Deng Zhenyong, Zhang Qiang, Pu Jinyong, et al. The impact of climate warming on crop planting and production in Northwestern China[J]. Acta Ecologica Sinica, 2008, 28(8): 3760-3768. doi: 10.1016/S1872-2032(08)60076-1
[3]	王改玲, 江山, 张菁, 等. 安太堡露天矿不同复垦年限苜蓿地土壤养分化学计量特征[J]. 草地学报, 2018, 26(5): 1118-1123.
	[ Wang Gailing, Jiang Shan, Zhang Jing, et al. Soil stoichiometric characteristics of alfalfa pasture of different restoration years in Antaibao opencast coal mine[J]. Acta Agrestia Sinica, 2018, 26(5): 1118-1123. ]
[4]	Torgny N, Ekblad A, Nordin A, et al. Boreal forest plants take up organic nitrogen[J]. Nature, 1998, 392(6679): 914-916. doi: 10.1038/31921
[5]	张燕江, 王俊鹏, 王瑜, 等. 农牧交错带典型区土壤氮磷空间分布特征及其影响因素[J]. 环境科学, 2021, 42(6): 3010-3017.
	[ Zhang Yanjiang, Wang Junpeng, Wang Yu, et al. Spatial patterns of nitrogen and phosphorus in soil and their influencing factors in a typical agro-pastoral ecotone[J]Environmental Science, 2021, 42(6): 3010-3017. ]
[6]	许轲, 孙圳, 霍中洋, 等. 播期、品种类型对水稻产量、生育期及温光利用的影响[J]. 中国农业科学, 2013, 46(20): 4222-4233.
	[ Xu Ke, Sun Zhen, Huo Zhongyang, et al. Effects of seeding date and variety type on yield, growth stage and utilization of temperature and sunshine in rice[J]. Scientia Agricultura Sinica, 2013, 46(20): 4222-4233. ]
[7]	袁俊秀. 播期对武威灌区春小麦产量和品质性状的影响[D]. 兰州: 甘肃农业大学, 2007.
	[ Yuan Junxiu. Effects of Sowing Date on Yield and Flour Quality of Spring Wheat in Wuwei Irrigation Area[D]. Lanzhou: Gansu Agricultural University, 2007. ]
[8]	王钧, 李广, 闫丽娟, 等. 旱地春小麦产量对不同生育阶段温度变化的响应模拟[J]. 中国农业科学, 2020, 53(5): 904-916.
	[ Wang Jun, Li Guang, Yan Lijuan, et al. Simulation of spring wheat yield response to temperature changes of different growth stages in drylands[J]. Scientia Agricultura Sinica, 2020, 53(5): 904-916. ]
[9]	张志新. 陇东黄土高原4种一年生牧草对播期的响应[D]. 兰州: 兰州大学, 2017.
	[ Zhang Zhixin. Responses of Four Annual Forages to Sowing Date in the Longdong Loess Plateau of China[D]. Lanzhou: Lanzhou University, 2017. ]
[10]	刘振杰, 李鹏飞, 黄世威, 等. 小麦秸秆生物质炭施用对不同耕作措施土壤碳含量变化的影响[J]. 环境科学, 2021, 42(6): 3000-3009.
	[ Liu Zhenjie, Li Pengfei, Huang Shiwei, et al. Effects of wheat straw-derived biochar application on soil carbon content under different tillage practices[J]. Environmental Science, 2021, 42(6): 3000-3009. ]
[11]	安崇霄, 张永杰, 杜孝敬, 等. 不同耕作措施对伊犁河谷夏大豆农田土壤碳排放、碳平衡及经济效益的影响[J]. 生态学杂志, 2020, 39(3): 812-821.
	[ An Chongxiao, Zhang Yongjie, Du Xiaojing, et al. Effects of different tillage measures on soil carbon emission, carbon balance and economic benefits of summer soybean cropland in Ili River Valley[J]. Chinese Journal of Ecology, 2020, 39(3): 812-821. ]
[12]	杨艳, 刘丹, 张霞, 等. 渭北旱塬不同耕作措施对土壤养分分布及作物产量的影响[J]. 干旱地区农业研究, 2018, 36(1): 171-178.
	[ Yang Yan, Liu Dan, Zhang Xia, et al. Effects of different tillage practices on nutrient distribution in soil profile and crop yield in Weibei Highland[J]. Agricultural Research in the Arid Areas, 2018, 36(1): 171-178. ]
[13]	Franzluebber A J, Schomberg H H, Endale D M. Surface-soil responses to paraplowing of long-term no-tillage cropland in the Southern Piedmont USA[J]. Soil & Tillage Research, 2007, 96(1-2): 303-315.
[14]	罗珠珠, 蔡立群, 李玲玲, 等. 长期保护性耕作对黄土高原旱地土壤养分和作物产量的影响[J]. 干旱地区农业研究, 2015, 33(3): 171-176.
	[ Luo Zhuzhu, Cai Liqun, Li Lingling, et al. Long-term effects of tillage system on soil nutrients and grain yields in rainfed area of Loess Plateau[J]. Agricultural Research in the Arid Areas, 2015, 33(3): 171-176. ]
[15]	Varvel G E, Wilhelm W W. No-tillage increases soil profile carbon and nitrogen under long-term rainfed cropping systems[J]. Soil & Tillage Research, 2011, 114(1): 28-36.
[16]	孔维萍, 成自勇, 张芮, 等. 保护性耕作在黄土高原的应用和发展[J]. 干旱区研究, 2015, 32(2): 240-250.
	[ Kong Weiping, Cheng Ziyong, Zhang Rui, et al. Application and development of conservation tillage techniques in the Loess Plateau[J]. Arid Zone Research, 2015, 32(2): 240-250. ]
[17]	祁剑英, 马守田, 刘冰洋, 等. 保护性耕作对土壤有机碳稳定化影响的研究进展[J]. 中国农业大学学报, 2020, 25(1): 1-9.
	[ Qi Jianying, Ma Shoutian, Liu Bingyang, et al. Advances in effects of conservation tillage on soil organic carbon stabilization[J]. Journal of China Agricultural University, 2020, 25(1): 1-9. ]
[18]	白帆, 杨晓光, 刘志娟, 等. 气候变化背景下播期对东北三省春玉米产量的影响[J]. 中国生态农业学报, 2020, 28(4): 480-491.
	[ Bai Fan, Yang Xiaoguang, Liu Zhijuan, et al. Effects of sowing dates on grain yield of spring maize in the Three-Province of the Northeast China under climate change[J]. Chinese Journal of Eco-Agriculture, 2020, 28(4): 480-491. ]
[19]	杨宁, 潘学标, 张立祯, 等. 适宜播期提高农牧交错带春小麦产量和水氮利用效率[J]. 农业工程学报, 2014, 30(8): 81-90.
	[ Yang Ning, Pan Xuebiao, Zhang Lizhen, et al. Optimal sowing dates improving yield, water and nitrogen use efficiencies of spring wheat in agriculture and pasture ecotone[J]. Transactions of the Chinese Society of Agricultural Engineering, 2014, 30(8): 81-90. ]
[20]	魏孔梅, 杨继忠, 张克厚, 等. 播期和播量对春小麦银春10号产量的影响[J]. 中国种业, 2020(8): 72-75.
	[ Wei Kongmei, Yang Jizhong, Zhang Kehou, et al. Effects of sowing date and sowing rate on the yield of spring wheat Yinchun 10[J]. China Seed Industry, 2020(8): 72-75. ]
[21]	董莉霞, 李广, 逯玉兰, 等. 定西42号小麦适宜播种期研究[J]. 作物研究, 2020, 34(5): 408-413.
	[ Dong Lixia, Li Guang, Lu Yulan, et al. Study on suitability of sowing date of wheat Dingxi NO. 42[J]. Crop Research, 2020, 34(5): 408-413. ]
[22]	王海燕. 陇中黄土丘陵区不同耕作措施对春小麦土壤水分利用效率的影响[D]. 兰州: 甘肃农业大学, 2018.
	[ Wang Haiyan. Effects of Different Tillage Measures on Soil Water Use Efficiency of Spring Wheat in Longzhong Loess Hilly Area[D]. Lanzhou: Gansu Agricultural University, 2018. ]
[23]	胡亚伟, 孙若修, 申明爽, 等. 晋西黄土区土地利用方式对土壤C: N: P化学计量特征及土壤理化性质的影响[J/OL]. 干旱区研究: http://kns.cnki.net/kcms/detail/65.1095.X.20210610.1309.003.html, 2021-06-11/2021-06-22.
	[ Hu Yawei, Sun Ruoxiu, Shen Mingshuang, et al. Effects of land use types on the stoichiometric characteristics of soil C∶N∶P and the physical and chemical properties of soil in Western Shanxi loess region[J/OL]. Arid Zone Research: http://kns.cnki.net/kcms/detail/65.1095.X.20210610.1309.003.html, 2021-06-11/2021-06-22. ]
[24]	马楚奇, 李广, 王钧, 等. 基于APSIM模型探讨耕作措施对春小麦产量的影响[J]. 热带农业工程, 2020, 44(2): 67-71.
	[ Ma Chuqi, Li Guang, Wang Jun, et al. Effect of farming practices on spring wheat yield by using APSIM model[J]. Tropical Agricultural Engineering, 2020, 44(2): 67-71. ]
[25]	聂志刚, 任新庄, 李广, 等. 基于APSIM的黄土丘陵区旱地小麦气候适宜性评价[J]. 中国农业气象, 2017, 38(6): 369-377.
	[ Nie Zhigang, Ren Xinzhuang, Li Guang, et al. APSIM-based evaluation of climatic suitability on wheat in dryland in the hill-gullied region of the Loess Plateau[J]. Chinese Journal of Agrometeorology, 2017, 38(6): 369-377. ]
[26]	Wu Jiangqi, Wang Haiyan, Li Guang, et al. Responses of CH₄ flux and microbial diversity to changes in rainfall amount and frequencies in a wet meadow in the Tibetan Plateau[J]. Catena, 2021, 202: 105253. doi: 10.1016/j.catena.2021.105253
[27]	袁建钰, 李广, 闫丽娟, 等. 黄土高原不同灌水量下春小麦土壤与植物碳氮磷含量及其化学计量比特征[J]. 草业科学, 2020, 37(9): 1803-1812.
	[ Yuan Jianyu, Li Guang, Yan Lijuan, et al. Soil and plant carbon, nitrogen, and phosphorus content and their stoichiometry in spring wheat under different irrigation treatments in the Loess Plateau[J]. Pratacultural Science, 2020, 37(9): 1803-1812. ]
[28]	张统帅, 闫丽娟, 李广, 等. 免耕和秸秆覆盖对旱作区土壤氮素、水分和春小麦产量的影响[J]. 浙江农业学报, 2020, 32(8): 1329-1341.
	[ Zhang Tongshuai, Yan Lijuan, Li Guang, et al. Effects of no tillage and straw mulching on soil nitrogen, water content and yield of spring wheat in dryland farming area[J]. Acta Agriculturae Zhejiangensis, 2020, 32(8): 1329-1341. ]
[29]	Rutigliano F A, Ascoli R D. Soil microbial metabolism and nutrient status in a Mediterranean area as affected by plant cover[J]. Soil Biology and Biochemistry, 2004, 36(11): 1719-1729. doi: 10.1016/j.soilbio.2004.04.029
[30]	张安宁, 刘任涛, 陈蔚, 等. 干旱区气候因子对枯落物分解和土壤动物的影响[J]. 干旱区研究, 2021, 38(3): 867-874.
	[ Zhang Anning, Liu Rentao, Chen Wei, et al. Effects of climatic factors on litter decomposition and soil fauna in arid area[J]. Arid Zone research, 2021, 38(3): 867-874. ]
[31]	胡锦昇, 樊军, 付威, 等. 保护性耕作措施对旱地春玉米土壤水分和硝态氮淋溶累积的影响[J]. 应用生态学报, 2019, 30(4): 1188-1198.
	[ Hu Jinsheng, Fan Jun, Fu Wei, et al. Effects of conservation tillage measures on soil water and $NO_3^--N$ leaching in dryland maize cropland[J]. Chinese Journal of Applied Ecology, 2019, 30(4): 1188-1198. ]
[32]	赵小星. 黄土高原不同耕作措施对耕层土壤水氮及春小麦氮素特征的影响[D]. 兰州: 甘肃农业大学, 2019.
	[ Zhao Xiaoxing. Effects of Different Tillage Practices on Soil Moisture and Nitrogen Characteristics of Spring Wheat in the Loess Plateau[D]. Lanzhou: Gansu Agricultural University, 2019. ]
[33]	窦超银, 于秀琴, 于景春. 辽西半干旱区播种期对春小麦生长发育·产量和耗水规律的影响[J]. 安徽农业科学, 2012, 40(25): 12441-12443.
	[ Dou Chaoyin, Yu Xiuqin, Yu Jingchun. Effect of sowing date on the growth and development and water consumption law of spring wheat (Triticum aestivum Linn.)[J]. Journal of Anhui Agricultural Sciences, 2012, 40(25): 12441-12443. ]
[34]	李明, 李朝苏, 刘淼, 等. 耕作播种方式对稻茬小麦根系发育、土壤水分和硝态氮含量的影响[J]. 应用生态学报, 2020, 31(5): 1425-1434. doi: 10.13287/j.1001-9332.202005.027 pmid: 32530218
	[ Li Ming, Li Chaosu, Liu Miao, et al. Effects of different tillage and sowing practices on root growth, soil moisture, and soil nitrate nitrogen content of wheat after rice[J]. Chinese Journal of Applied Ecology, 2020, 31(5): 1425-1434. ] doi: 10.13287/j.1001-9332.202005.027 pmid: 32530218
[35]	张建军, 党翼, 赵刚, 等. 留膜留茬免耕栽培条件下旱作玉米生长季土壤氮素供应动态特征[J]. 中国农业科技导报, 2020, 22(2): 132-139.
	[ Zhang Jianjun, Dang Yi, Zhao Gang, et al. Dynamic characteristics of soil nitrogen supply in maize growing season of no-tillage plastic film and stubbles with residues in dryland[J]. Journal of Agricultural Science and Technology, 2020, 22(2): 132-139. ]
[36]	Tian H Q, Chen G S, Zhang C, et al. Pattern and variation of C: N: P ratios in China’s soils: A synthesis of observational data[J]. Biogeochemistry, 2010, 98(1/2/3): 139-151. doi: 10.1007/s10533-009-9382-0
[37]	朱秋莲. 黄土丘陵区不同植被带立地条件对植物—枯落物—土壤生态化学计量特征的影响[D]. 杨凌: 西北农林科技大学, 2013.
	[ Zhu Qiulian. The Effects of Slope Condition on Leaf-Litter-Soil Stoichiometry on the Hilly-Gully Area of Loess Plateau[D]. Yangling: Northwest A&F University, 2013. ]
[38]	李恩慧, 王玉慧, 杨慎骄, 等. 晋西南褐土上小麦苜蓿套作对土壤氮素及植物吸氮的影响[J]. 中国土壤与肥料, 2020(6): 114-121.
	[ Li Enhui, Wang Yuhui, Yang Shenjiao, et al. Effects of alfalfa-wheat intercropping systems on soil nitrogen and plant nitrogen uptake in cinnamon soil of Southwest Shanxi province[J]. Soil and Fertilizer Sciences in China, 2020(6): 114-121. ]
[39]	何文寿, 何进勤, 王菊兰, 等. 宁夏引黄灌区春小麦不同生育期土壤有效氮磷钾养分含量的动态变化特点[J]. 西北农业学报, 2006, 15(3): 54-59.
	[ He Wenshou, He Jinqin, Wang Julan, et al. Variation of soil available nutrient contents in farmlands at different growth stages of spring wheat in irrigating region of Ningxia[J]. Acta Agriculturae Boreali-Occidentalis Sinica, 2006, 15(3): 54-59. ]
[40]	张英英, 蔡立群, 张仁陟, 等. 不同耕作措施对春小麦生育期内土壤酶活性的影响[J]. 干旱区资源与环境, 2016, 30(10): 88-92.
	[ Zhang Yingying, Cai Liqun, Zhang Renzhi, et al. Effects of different tillage methods on soil enzyme activities during growth period of spring wheat in the Loess Plateau of central Gansu Province[J]. Journal of Arid Land Resources and Environment, 2016, 30(10): 88-92. ]

处理	TN			TP			N∶P
处理	标准差	均值/（g·kg^-1）	CV/%	标准差	均值/（g·kg^-1）	CV/%	标准差	均值	CV/%
T	0.076	0.173BCD	44.06	0.046	0.103B	44.40	1.262	1.980A	63.73
TS	0.082	0.208AB	39.55	0.042	0.112AB	37.27	1.030	2.075A	49.62
NT	0.070	0.193ABC	36.13	0.047	0.106AB	44.14	1.222	2.009A	60.85
NTS	0.076	0.222A	34.03	0.067	0.138A	48.96	1.390	1.976A	70.35
ET	0.044	0.131E	33.71	0.067	0.115AB	58.39	0.651	1.333B	48.86
ETS	0.056	0.159CDE	34.98	0.039	0.117AB	33.43	0.427	1.448B	29.51
ENT	0.053	0.152DE	35.21	0.042	0.119AB	35.31	0.351	1.302B	26.99
ENTS	0.057	0.172BCD	33.25	0.043	0.115AB	37.13	0.476	1.583AB	30.09

	T						TS
	$NO_3^--N$		$NH_4^+-N$		TP		$NO_3^--N$		$NH_4^+-N$		TP
	早播	正常播	早播	正常播	早播	正常播	早播	正常播	早播	正常播	早播	正常播
TN_SD	0.262	0.289	0.265	0.516^**	0.438^**	0.129	0.219	0.273	0.368^*	0.532^**	0.622^**	0.309^*
$NO_3^--N$_SD	1.000	1.000	0.400^**	0.490^**	-0.056	-0.081	1.000	1.000	0.337^*	0.337^*	0.082	-0.065
$NH_4^+-N$_SD			1.000	1.000	0.273	0.287			1.000	1.000	0.130	0.213
	NT						NTS
	$NO_3^--N$		$NH_4^+-N$		TP		$NO_3^--N$		$NH_4^+-N$		TP
	早播	正常播	早播	正常播	早播	正常播	早播	正常播	早播	正常播	早播	正常播
TN_SD	0.390^*	0.237	0.361^*	0.638^**	0.768^**	0.491^**	0.270	0.279	0.274	0.680^**	0.675^**	0.515^**
$NO_3^--N$_SD	1.000	1.000	0.325^*	0.438^**	0.044	-0.180	1.000	1.000	0.041	0.449^**	0.251	0.491^**
$NH_4^+-N$_SD			1.000	1.000	0.293	0.383^**			1.000	1.000	0.070	0.641^**