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Improvement of Partial Root-Zone Soil Environment Increases Salinity Tolerance of Cotton Hezhong Dong, L.I. Weijiang and L.I. Zhenhuai Cotton Research Center/Shandong Provincial Key Lab for Cotton Culture and Physiology, Shandong Academy of Agricultural Sciences, Jinan–250100, P.R. China E-mail:
[email protected] Abstract—Soil salinity is a major threat to cotton production worldwide. The objective of this study was to test whether improvement at least in a part of the root-zone environment would enhance tolerance salinity and alleviate salinity injury. Five experiments were conducted using a split-root system in the greenhouse or furrow seeding with or without plastic mulching under salt-affected field conditions. The results showed that plastic mulching, furrow seeding and early mulching or late-planting with short-season cotton either resulted in unequal salt distribution, or increased moisture and temperature in the root-zone, and effectively reduced salt-injury to cotton. It is concluded that improved partial root-zone environment increases salinity tolerance of cotton. Keywords: Cotton, Salinity stress, Root-zone environment, Salinity tolerance, Plastic mulching
INTRODUCTION Soil salinity has been a major concern to global agriculture throughout human history (Lobell et al.,, 2007). In recent times, it has become even more prevalent with intensification of land use (Meloni et al., 2003, Egamberdieva et al., 2010). Cotton, though classified as one of the most salt-tolerant major crops, its growth and development as well as yield and fiber quality are negatively affected by excessive salts in the soil (Maas and Hoffman 1977, Qadir and Shams 1997, Higbie et al.,, 2010). Cotton is a pioneer crop in reclamation of saline soils. But potential depends largely on ways and means to improve salt tolerance of cotton. Although, some progress was made in salt-tolerance improvement, the development of salttolerant cotton is not an easy job due to the complexity of the tolerance mechanisms and narrow germplasm resource. There are a number of agronomic practices which can effectively control salt damage through improvement in root-zone soil environment. Soil salinity expressed by ECe (electrical conductivity of a saturated-paste extract), with values of 7.7, 12.5, and 17.1 dS m−1 are referred to as low, moderate and high salinity level, respectively (Chen et al.,, 2009, Maas and Grattan, 1999). In general, soil salinity delays and reduces germination and emergence, decreases cotton shoot growth, and finally leads to reduced seed cotton yield and fiber quality characteristics at moderate to high salinity levels (Khorsandi and Anagholi, 2009). Since soil salinity and the related stress originate from the root-zone soil environment, it is hypothesized that improving at least part of the root-zone environment would alleviate salt injury. The hypothesis was tested in greenhouse and field experiments.
MATERIALS AND MEDHODS In a split-root experiment (EXP 1), potted cotton plants were grown in a split-root system in the greenhouse and each root half was irrigated with either the same or two concentrations of NaCl (Fig. 1). In a field experiment (EXP 2), we compared cotton grown on furrow-beds in saline fields with those grown on flat beds as controls. A separate field experiment was conducted to evaluate the effect of mulching with polyethylene film. Integration of plastic film with irrigation methods was also studied in a separate set of experiment. Details of treatments provided in Dong et al. (2009, 2010 a, 2010 b).
Improvem ment of Partial Root-Zone R Soil Environment E Inc creases Salinityy Tolerance of C Cotton
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Fig. 1: Effeccts of Unequal Salt Distribution (1000/500 mM NaCl) and a Equal Salt Distribution (300/300 mM NaCl) in cthhe Root-Zone on Cootton Seedling Groowth in the Green House.
RESULTS AND A DISCUSSION When thee entire root system was exposed to the same co oncentration of NaCl, leaaf area, plan nt biomass, leaf chlorrophyll (Chll) and photoosynthesis (P Pn) were sig gnificantly reduced r relaative to the NaCl-free control. However, H whhen only halff of the root system s was exposed e to loow-salinity, the inhibitio on effect of salinity on o growth annd yield waas significanntly reduced d. Plant biom mass and seeed cotton yield y were significanntly increasedd compared to t equal salt distribution (Dong et al.,, 2010b). Furrow w-bed seediing induced unequal saalt distribution in salinee fields; plaant growth, yield and earliness were significantly improoved. Such an a improvem ment in yieldd and earlineess was mainly due to unequal distribution d of salts in the root zone (D Dong et al., 2010b). 2 Row covering wiith polyethylene film ennhances plan nt growth byy increasingg soil temperature and water connservation. In I our field experiment (EXP 3), plastic p mulchhing also reesulted in un nequal salt distributioon in the salline soil, in which part of o the root system s develloped in relaatively low-ssaline soil. Further sttudy showedd that the integration of o plastic mu ulching withh furrow seeeding enhan nced stand establishm ment, earliness, yield, andd yield compponents of co otton more thhan effectiveely mulching g or furrow seeding allone (Fig. 2) (Dong et al.., 2008).
a
b
c
Fig. 2: Effects of Seeding Modes onn Stand Establishment in a Saaline Field. Convventional Seediing without Mulching (a), Conventional C Seeeding under Mulching M (b) andd Furrowing Seeeding under Mulching M Resulteed in Poor, Modderate and Full Standd Establishmentt, Respectivelyy Norm mal planting of full-seasoon cotton in saline fields in temperaate areas is faced with poor p stand establishm ment, late maturity, m and increasing cost of inpu uts. After tryying late plaanting of sh hort-season cotton in a saline fieldd of the Yelloow River Deelta (EXP 4),, we observeed that late planting of sh hort-season cotton siggnificantly im mproved seeed emergencce and seedlling growth due to increeased tempeerature and reduced Na+ N concentrration in cotton tissues relative to norm mal plantingg ( Dong et al.,, 2010a).
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World Cotton Research Conference on Technologies for Prosperity
Row mulching is conventionally applied after sowing, but pre-sowing evaporation in spring would cause accumulation of salts and moisture loss in the surface layer of saline soils. Row mulching with plastic film can be done 30 d before sowing (early mulching) in saline fields (EXP 5). Although both conventional and early mulching could effectively improve stand establishment, plant growth, earliness and lint yield of cotton, early mulching was more beneficial to stand establishment, plant growth and yield. The increased benefits of early mulching were due mainly to the better control of root-zone soil salinity, elevation of soil temperature and reduction of moisture loss (Dong et al., 2009).
CONCLUSION About 23% of the world’s cultivated lands are saline. Plastic mulching, furrow seeding, late-planting of short season-cotton, irrigation and fertilization either reduced salinity, increased temperature and moisture, or increased supply of nutrients in the soil root-zone, thus reducing the salt damage in saline fields. We conclude that improvement in a part of the root-zone environment increases salinity tolerance of cotton.
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