Use Of Saline Aquaculture Effluent To Irrigate Salt-Tolerant Crops, Jerusalem Artichoke And Sunflower, In The Laizhou Bay Region

There are 18,000 km coastline and more than 2 million hectares of coastal salinizedland in China. From 1980's, with the exploitation of these land, local resources andenvironments were severely devastated. The shortage of freshwater, soil salinity,contamination of aquafarm and offshore pollution become major problems influencingand restricting the sustainable development of agriculture and fishery economies. On thebase of resources and environments not been ruined, how to efficiently use presentresources to develop economies in coastal zones is a critical problem needed to solve assoon as quickly. Aquaculture effluent which is derived from aquafarms, contains avariety of nutrients, such as nitrogen, phosphorus and organisms. If it is directlydischarged into sea without pre-treated, which can cause offshore pollution. Accordingto the rational configuration of water and land resources, use of saline aquacultureeffluent to irrigate salt-tolerant crops, i.e., establishment of compound seawateragriculture and fishery ecosystems is the best way to solve aforementioned problems.From 2004 to 2005, lysimeter, microplot, ¹⁵N-isotope tracer and field experiments wereconducted to study water, salt and nutrient fluxes, effect of irrigation with salineaquaculture effluent on soil safety, crop growth and yield, as well as groundwaterenvironments. In addition, Watsuit model recommended by FAO was used to assess thesafety of soil-plant systems in order to provide theoretical and practical bases forestablishment of compound seawater agriculture and fishery ecosystems.1. Lysimeter, microplot and ¹⁵N isotope tracer experiments were performed to studywater, salt and nutrient fluxes under irrigation with saline aquaculture effluent during theJerusalem artichoke and sunflower growing season. The results in lesimeter experimentshow that: (1) For the different leaching fraction(LF) of being 0.1, 0.2, 0.3 and 0.4, thesaline aquaculture effluent used for evaportranspiration (ET) accounts for 36.5, 36.2,37.0 and 37.3% of total ET of Jerusalem artichoke respectively, and the effective precipitationused for ET 49.5, 46.3, 41.9 and 38.7% respectively; during the sunflower growingseason, the saline aquaculture effluent used for ET accounts for 40.3, 45.3, 50.2 and60.0% of total ET respectively. For the different leaching fraction(LF) of being 0.1, 0.2,0.3 and 0.4, the dissolved salts entering into soil through irrigation come up to 108.5,122.1, 139.5 and 162.8 g and those leaching into the deeper soil layer reach 17.5, 28.1,40.8 and 55.7 g, and the pure accumulation of the salts in the root zone reaches 91.0,94.0, 98.7 and 107.1 g respectively during the Jerusalem artichoke growing season;similarly, during the sunflower growing season, the dissolved salts entering into soilthrough irrigation come up to 54.3, 61.1, 69.8 and 81.4 g and those leaching into thedeeper soil layer reach 15.8, 27.9, 37.4 and 52.8 g, and the pure accumulation of the saltsin the root zone reaches 38.5, 33.2, 32.4 and 28.6 g respectively. For the differentleaching fraction of being 0.1, 0.2, 0.3 and 0.4, NH₄-N entering into soil throughirrigation come up to 2.37, 2.67, 3.05 and 3.56 mg respectively and those leaching intothe deeper soil layer reach 0.37, 0.38, 0.79 and 0.75 mg, and the pure accumulation ofNH₄-N in the root zone reaches 2.00, 2.29, 2.27 and 2.82 mg respectively; NO₃-Nentering into soil through irrigation come up to 9.84, 11.07, 12.64 and 14.76 mg andthose leaching into the deeper soil layer reach 8.03, 9.20, 11.35 and 13.84 mg, and thepure accumulation of NO₃-N in the root zone reaches 1.81, 1.40, 1.29 and 0.92 mgrespectively; PO₄-P entering into soil through irrigation come up to 4.41, 4.96, 5.67 and6.61 mg and those leaching into the deeper soil layer reach 1.38, 2.28, 3.23 and 4.95 mg,and the pure accumulation of PO₄-P in the root zone reaches 3.03, 2.68, 2.44 and 1.67mg respectively during the Jerusalem artichoke growing season. Similarly, during thesunflower growing season, NH₄-N entering into soil through irrigation come up to 2.97,3.34, 3.80 and 4.45 mg and those leaching into the deeper soil layer reach 0.42, 0.58,0.75 and 0.58 mg, and the pure accumulation of NH₄-N in the root zone reaches 2.55,2.76, 3.06 and 3.88 mg respectively; NO₃-N entering into soil through irrigation comeup to 5.18, 5.82, 6.65 and 7.76 mg and those leaching into the deeper soil layer reach8.03, 9.20, 11.35 and 13.84 mg, and the pure accumulation of NO₃-N in the root zonereaches -0.63, -3.96, -2.05 and -0.77 mg respectively; PO₄-P entering into soil throughirrigation come up to 1.53, 1.72, 1.96 and 2.29 mg and those leaching into the deepersoil layer reach 0.78, 1.00, 1.54 and 2.72 mg, and the pure accumulation of PO₄-P in theroot zone reaches 0.75, 0.71, 0.45 and -0.43 mg respectively. The results obtained through microplot experiment show that (1) the Total ET ofJerusalem artichoke in CK1, CK2, 1:1, 1:2, 1:3 and 1:4 treatments are 456.0, 747.6,673.9, 684.8, 720.8 and 722.0 mm respectively and those of sunflower 243.9, 409.8,364.1, 372.9, 381.0 and 372.6 mm respectively. For the saline aquaculture effluenttreatments of 1:1, 1:2, 1:3 and 1:4, the total dissolved salts entering into a microplotthrough irrigation come up to 6960.0, 5070.0, 4110.0 and 3534.0 g and those leachinginto the deeper soil layer reach 1302.6, 1134.0, 812.4 and 711.0 g, and the pure saltaccumulation in the root zone reaches 5687.4, 3936.0, 3297.6 and 2823.0 g respectivelyduring the Jerusalem artichoke growing season. Similarly, during the sunflower growingseason, the dissolved salts entering into a microplot through irrigation come up to 2688.0,1971.0, 1614.0 and 1398.0 g and those leaching into the deeper soil layer reach 774.0,601.8, 397.8 and 402.0 g, and the pure salt accumulation in the root zone reaches 38.5,33.2, 32.4 and 28.6 g respectively. For the saline aquaculture effluent treatments of 1:1,1:2, 1:3 and 1:4, NH₄-N entering into a microplot through irrigation come up to 336.0,276.0, 246.0 and 228.0 mg and those leaching into the deeper soil layer reach 123.0,154.8, 141.6 and 84.0 mg, and the pure NH₄-N accumulation in the root zone reaches213.0, 121.2, 104.4 and 144.0 mg respectively during the Jerusalem artichoke growingseason; NO₃-N entering into a microplot through irrigation come up to 942.0, 750.0,648.0 and 594.0 mg and those leaching into the deeper soil layer reach 631.0, 300.6,334.2 and 333.0 mg, and the pure NO₃-N accumulation in the root zone reaches 411.0,449.4, 313.8 and 261.0 mg respectively; PO₃-P entering into a microplot throughirrigation come up to 438.0, 360.0, 318.0 and 294.0 mg and those leaching into thedeeper soil layer reach 244.8, 174.6, 277.8 and 227.4 mg, and the pure PO₃-Paccumulation in the root zone reaches 193.2, 185.4, 40.2 and 66.6 mg, respectively.Similarly, for the saline aquaculture effluent treatments of 1:1, 1:2, 1:3 and 1:4, NH₄-Nentering into a microplot through irrigation come up to 201.0, 162.0, 144.0 and 132.0 mgand those leaching into the deeper soil layer reach 72.6, 93.6, 88.8 and 62.4 mg, and thepure NH₄-N accumulation in the root zone reaches 128.4, 68.4, 55.2 and 69.6 mg,respectively; NO₃-N entering into a microplot through irrigation come up to 654.0, 492.0,411.0 and 360.0 mg and those leaching into the deeper soil layer reach 262.8, 225.6,331.8 and 209.4 mg, and the pure NO₃-N accumulation in the root zone reaches 391.2,266.4, 79.2 and 150.6 mg, respectively; PO₃-P entering into a microplot throughirrigation come up to 171.0, 132.0, 114.0 and 105.0 mg and those leaching into the deeper soil layer reach 109.2, 112.2, 87.0 and 103.2 mg, and the pure PO₃-Paccumulation in the root zone reaches 61.8, 19.8, 27.0 and 1.8 mg respectively duringthe sunflower growing season.The results obtained through ¹⁵N isotope tracer experiment indicate that, 26.1 and27.6% of N in the saline aquaculture effluent are uptaken by Jerusalem artichoke andsunflower, respectively; 45.0 and 40.31% are adsorbed by soil particles for Jerusalemartichoke and sunflower, respectively; 28.9 and 32.09% are volatilized or leached forJerusalem artichoke and sunflower, respectively.2. Microplot experiments were conducted to study the effect of irrigation with salineaquaculture effluent on soil safety. The results are as follows: (1) ECe in salineaquaculture effluent treatments significantly increased as compared with non-irrigated orfreshwater treatment, and ECe increased with increasing salinity of irrigated water. ECehad no significant differences among various saline aquaculture effluent treatments,indicating pre-irrigation with freshwater plays a important role in leaching salt out of theroot zone. (2) Saline aquaculture effluent irrigation significantly increased the soilsolution concentration, the values of which were more than 33.1 and 20.0 g L^-1 duringthe Jerusalem artichoke and sunflower growing season, respectively. (3)Salineaquaculture effluent irrigation had a significant effect on pHs, and with an increase insalinity of the irrigated water, pHs also increased. The pHs values of saline aquacultureeffluent treatments of 1:1,1:2 and 1:3 were significantly higher than non-irrigated orfreshwater treatment. (4) The SARs under irrigation with saline aquaculture effluentwere significantly higher than non-irrigated or freshwater treatment, and the SARsincreased with increasing salinity of irrigated water. (5) Highly saline aquaculture didpromote the soil infiltration capacity. (6) Soil moisture in the upper layer was greatlyaffected by climatic factors such as rainfall and evapotranspiration, therefore displayed avast fluctuation; however, the deeper layer was on the contrary. Soil moisture increasedwith increasing depth of soil layers. (7) Na⁺ and Cl^- contents in 0-60 cm soil layer werehigher in saline aquaculture effluent treatment than those in control treatment.(8) Thereare no significant differences in N content among all treatments; the available P, however,has significant different in 0-20 cm soil layer of 1:4 treatment as compared with othertreatments.3. Effect of irrigation with saline aquaculture effluent on growth and yield of Jerusalem artichoke and sunflower was also studied. The results are as follows: (1) Under a lowersalinity of irrigated water conditions, the plant height of Jerusalem artichoke wasdecreased, but plant diameter was increased, indicating the plant shape had beenimproved under relatively lower salt stress. However, the plant height and stem diameterof sunflower significantly decreased as compared with non-irrigated or freshwatertreatment, suggesting that salt stress significantly inhibited sunflower growth. (2) Theabove-ground biomass was influenced under saline aquaculture effluent irrigation, butbelow-ground biomass was improved at a suitable salinity level. However, biomass ofsunflower was significantly decreased under freshwater or saline aquaculture effluentirrigation, indicating sunflower has a important trait of draught-tolerance. (3) The tuberyield of Jerusalem artichoke in 1:3 and 1:4 treatments was significantly higher thannon-irrigated or freshwater irrigation treatment, demonstrating that relatively lower saltstress could improve the tuber growth. However, all saline aquaculture effluent treatmentexcerpt for 1:4 caused a significant decrease in seed yield of sunflower compared withnon-irrigated treatment, indicating irrigation has a negative effect on seed yield undernormal climatic conditions in Laizhou region. (4) Harvest index(HI) of Jerusalemartichoke is higher under relatively lower salinity of irrigated water, but for sunflower itis higher under relatively higher salinity of irrigated water.(5) The threshold salinity ofirrigated water for Jerusalem artichoke is 5.97 dS m^-1, and the relative tuber yielddecreases by 5.21% with 1 dS m^-1 increasing of irrigated water. The salt-tolerantequation is Yr=100-5.21(ECw-5.97). The threshold salinity of irrigated water forsunflower is 2.18 dS m^-1, and the relative seed yield decreases by 5.80% with 1 dS m^-1increasing of irrigated water. The salt-tolerant equation is Yr=100-5.80(ECw-2.18). (6)Saline aquaculture effluent irrigation has a decline trend in water use efficiency ascompared with non-irrigation or freshwater irrigation treatment. (7) Magnitude of Na⁺content in terms of treatments are CK2＜CK2＜CK3＜1:4＜1:2＜1:1. The Na⁺ content is thehighest in roots rather than stems, leaves and tubers under saline aquaculture effluentirrigation, and Na⁺ was mainly accumulated in roots and stems rather than leaves ortubers; however, Cl^- was largely accumulated in roots, stems, leaves and tubers. (8)Freshwater irrigation promoted N and P uptake by Jerusalem artichoke and sunflower,but saline aquaculture effluent inhibited. Therefore, we draw a conclusion that thesalinity of irrigated water is a major factor influencing N and P uptake by plant.4. Two wells were installed in experimental and non-experimental sites, in order to reveal the effect of irrigation with saline aquaculture effluent on groundwater qualities.The results show that: (1)The EC of groundwater had not significant differences betweenexperimental and non-experimental sites, and the changes in EC was less than 2 dS m^-1.(2) The nitrate content ranged from 4.0 to 5.0 mg L^-1, setting in the groundwater qualitystandard ofâ…¡. (3) The ammonia content ranged from 0.05 to 0.31 mg L^-1, setting in thegroundwater quality standard ofâ…¡-â…£. (4) Phosphate content of groundwater was alsolow. Statistical results show that electrical conductivity and the contents of nitrate,ammonia and phosphate in groundwater had not significant differences between twowells, indicating saline aquaculture effluent irrigation could not contaminategroundwater.5. Watsuit model recommended by FAO was used to evaluate the safety of soil-plantsystems under irrigation with saline aquaculture effluent during the Jerusalem artichokeand sunflower growing seasons. The results show that: (1) The ECe of 1:3 and 1:4 salineaquaculture effluent treatments in the root zone range from 3.0 to 6.0 dS m^-1, whichvalues were less than the threshold salinity of Jerusalem artichoke, therefore weconcluded it was safe using 1:3 and 1:4 saline aquaculture effluent to irrigate Jerusalemartichoke; ECe in each saline aquaculture effluent treatment for sunflower, however, wasmore than the threshold salinity of 3.0 dS m^-1, therefore saline aquaculture effluentirrigation had exerted negative effects on soil safety and crop yield. (2) SARs in salineaquaculture effluent treatments was much lower than that in rainfed or freshwaterirrigation treatment, and their values are less than 10 mmol^1/2L^-1/2, indicating that salineaquaculture effluent irrigation did not cause soil alkalinity. (3) The calcium contents inthe soil were more than 2 mmol L^-1, suggesting irrigation with saline aquacultureeffluent could not cause nutrient disturbance.