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Biomass accumulation and potential nutritive P.H. Robinson , S.R. Grattan , G. Getachew , C.M. Grieve , a Department of Animal Science, University of California, Davis, CA 95616, USA b Department of LAWR, University of California, Davis, CA 95616, USA c USDA-ARS Salinity Laboratory, 450 W. Big Springs Road, Riverside, CA 92507, USA d Department of Plant Science, California State University, Fresno, CA 93740, USA Received 2 December 2002; received in revised form 11 June 2003; accepted 11 June 2003 Abstract
A controlled study using a sand-tank system was conducted to evaluate 10 forage species (bermudagrass, ‘Salado’ and ‘SW 9720’ alfalfa, ‘Duncan’ and ‘Polo’ Paspalum, ‘big’ and ‘nar-row leaf’ trefoil, kikuyugrass, Jose tall wheatgrass, and alkali sacaton). Forages were irrigated withsodium-sulfate dominated synthetic drainage waters with an electrical conductivity of either 15 or25 dS/m. Forage yield was significantly reduced by the higher (25 dS/m) salinity level of irrigationwater compared to the lower (15 dS/m) level. There was wide variation in the sensitivity of foragespecies to levels of salinity in irrigation water as reflected by biomass accumulation. With the excep-tion of bermudagrass, which increased accumulation at the higher level of salinity, and big trefoil,which failed to establish at the higher level of salinity, ranking of forages according to the percentreduction in biomass accumulation due to the higher level of salinity of irrigation water was: Saladoalfalfa (54%) = SW 9720 alfalfa (52%) > Duncan Paspalum (41%) > narrow leaf trefoil (30%) >alkali sacaton (24%) > Polo Paspalum (16%) > Jose tall wheatgrass (11%) = kikuyugrass (11%).
Bermudagrass and Duncan Paspalum were judged to be the best species in terms of forage yieldand nutritive quality. Kikuyugrass, which had the third highest biomass accumulation, was judgedto be unacceptable due to its poor nutritional quality. Although narrow leaf trefoil had a relativelyhigh nutritional quality, its biomass accumulation potential was judged to be unacceptably low. Al-falfa cultivar’s biomass accumulations were the most sensitive to the higher level of salinity, among Abbreviations: CP, crude protein; DM, dry matter; dNDF, in vitro digestibility of NDF at 30 h; DW, dry weight; EE, ether extract; IVTD, in vitro true digestibility of DM; ME, metabolizable energy (ME, MJ/kg DM);OM, organic matter; NDF, neutral detergent fibre ∗ Corresponding author. Tel.: +1-530-752-7139; fax: +1-530-752-0175.
E-mail address: ggetachew@ucdavis.edu (G. Getachew).
0377-8401/$ – see front matter 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0377-8401(03)00213-X P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 forages that survived at the higher salinity level, although actual accumulations at the higher salinitywere high relative to other forages. Increased salinity influenced several forage quality parameters,including organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), and in vitro gasproduction, generally leading to higher nutritional quality at the higher salinity level, although theirsignificance varied amongst species and cuttings.
2003 Elsevier B.V. All rights reserved.
Keywords: Drainage; Salinity; Forage; Sodicity; Gas production 1. Introduction
Reuse of saline-sodic drainage water for irrigation is a necessary management op- tion on the west side of the San Joaquin Valley in California to reduce the volume ofdrainage water requiring disposal, without sacrificing the potential productivity of theland (). Several methods ofutilizing saline water (i.e. sequential, cyclic and blending) have been tested experimen-tally or are being demonstrated under field conditions (Reuseof drainage water is challenging from an irrigation management perspective in that thiswater is both saline (i.e. the electrical conductivity (EC) of the water is over 4 dS/m)and sodic (i.e. the sodium adsorption ratio (SAR)is greater than 15) (ter, 2003). Salinity reduces crop growth and sodicity can adversely affect soil structurethereby indirectly affecting plant growth by poor soil aeration and increased surface crustformation.
High quality forages for dairy cattle, beef cattle, and sheep are in short supply in the Central Valley of California. Identifying salt-tolerant forage crops that grow well under ir-rigation with saline drainage water would not only increase forage supplies, but would playa key role in drainage water management. Actual suitability of forages for reuse systems,however, will depend upon their production potential under saline-sodic conditions and thenutritional quality of the resulting forage. Although some studies have been conducted thataddress forage quality in salt-affected land (e.g. a consid-erable amount of additional research in this area is needed An interdisciplinary research team was developed involving scientists from the Univer- sity of California (Davis), USDA-ARS Salinity Laboratory (Riverside), and the CaliforniaState University (Fresno) with expertise in soils and irrigation management, plant physi-ology, salinity, plant nutrition, and ruminant nutrition. The overall objective of this studyis to evaluate a number of promising forage crops in terms of their biomass accumulationpotential and nutritional quality when irrigated with saline-sodic drainage water dominatedby sodium-sulfate.
1 SAR = Na+/[(Ca2++Mg2+)/2]1/2 when units are meq/l.
P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 2. Materials and methods
This experiment was conducted in greenhouse sand-tanks at the USDA-ARS Salinity Laboratory located on the campus of the University of California (Riverside, CA). Thesand-tank system creates a uniform and controlled rootzone environment such that ac-tual biomass accumulation among test forages can be compared. There were 30 tanks(1.2 m × 0.6 m × 0.5 m deep) filled with washed sand that had an average bulk densityof 1.4 g/cm3. Each tank was irrigated with a complete nutrient solution salinized to either15 or 25 dS/m (The salt solutions were prepared to simulate the composition ofpotential drainage waters, dominated by sodium and sulfate, common in the San JoaquinValley of California and based upon long term simulation predictions using UNSATCHEM(after establishment of cation exchange equilibrium. Tankswere irrigated thrice daily at 8 h intervals for 15 min durations. The irrigations resulted inwater saturation, after which the solutions drained to 765 l reservoirs below the sand-tanksfor reuse in the next irrigation. Thus, the salinity of the irrigation water was similar to thatof the sand water. The irrigation waters were regularly analyzed by inductively coupledplasma optical emission spectrometry to confirm that target ion concentrations were main-tained (Chloride in the solutions was determined by coulometric–amperometrictitration Water lost by evapo-transpiration was replenished automaticallyto maintain constant volumes and osmotic potentials in the irrigation waters.
Ten forages were grown in the sand-tanks at salinity levels of 15 or 25 dS/m, and each treatment was replicated thrice. The forage species were alfalfa (Medicago sativa) cvs.
Salado and SW 9720, narrow leaf trefoil (Lotus glaber), big trefoil (L. ulginosus), kikuyu-grass (Pennisetum clandestinum) cv. Whittet, alkali sacaton (Sporobolus airoides), Pas-palum (Paspalum vaginatum) cvs. Polo and Duncan, tall wheatgrass (Agropyron elonga-tum) cv. Jose, and bermudagrass (Cynodon dactylon) cv. Tifton. Forages were planted inthe sand-tanks in July or August, with the exception of bermudagrass which was plantedthe following January. Salinization began 4–6 week after planting, except for the Paspalumvarieties, which were salinized 20 week after planting, and bermudagrass which was di-rectly planted in salinized tanks. In each tank, two different forages were planted in a0.6 m × 0.6 m area, separated by a plastic partition extending 20 cm below and 10 cm above Table 1Ionic composition of the simulated drainage water treatments (mean and standard error) P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 the sand surface. With the exception of bermudagrass, all species were established in thetanks by irrigation with a complete nutrient solution prior to application of the salinitytreatments.
Harvest scheduling depended on the growth pattern of each forage species. For exam- ple, alfalfa cultivars were sampled at first flowering while alkali sacaton, kikuyugrass andtall wheatgrass were harvested based upon plant height, and the trefoils, Paspalums andbermudagrass were based upon estimated biomass accumulation. At each harvest, herbagewas cut 5–9 cm above the sand surface, weighed, washed in deionized water, and dried ina forced air oven at 70 ◦C for 72 h. Biomass is reported based on forage dry weight (DW).
2.3. In vitro and chemical analyses In vitro gas production was completed using 30 ml of buffered rumen fluid according to an in vitro gas method In this method, 200 mg of samplewas incubated in glass syringes with added rumen inoculum in a water bath at 39 ◦C, andgas production at 24 h was recorded and corrected for blank incubation (i.e. buffered ru-men fluid with no sample). Procedures of the Association of Official Analytical Chemistswere used for dry matter (DM), organic matter (OM; AOAC ID 967.05), andcrude fat (EE; AOAC ID 920.39). Crude protein (CP) was calculated from N determinedby sample combustion at high temperature in pure oxygen and measured by thermal con-ductivity detection (ID 990.03). In vitro true degradability (IVTD), neutraldetergent fiber (NDF), and in vitro digestibility of NDF at 30 h of incubation (dNDF) weredetermined by incubating the samples in multi-layer polyethylene polyester cloth bags asdescribed by Metabolizable energy (ME) values were predictedusing 24 h in vitro gas values combined with CP, and fat contents ( Forage quality determinations were statistically analyzed as a factorial experiment with salinity, forage species, cut number and the forage species by harvest interaction as factorsin the model. Means separation was carried out using Tukey’s studentized range test In a number of forage nutritive value descriptors, the cut number by forage interactionwas statistically significant (i.e. P < 0.05). Therefore, forages were statistically analyzedwithin cut number and data presented represent all forages at their first, third, and fifth cuts.
3. Results
Biomass accumulations of different forage species irrigated with saline water of 15 and 25 dS/m are in in bermudagrass (the biomass yield of forages at15 dS/m was higher than at 25 dS/m. The biomass yield of bermudagrass tended to increaseat the higher level of salinity in the irrigation water. There were strong linear relationships P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 Cumulative biomass yield (kg DM /ha)
Days after planting
Cumulative biomass yield (kg DM /ha)
Days after planting
Fig. 1. Cumulative forage biomass in relation to days after planting for the alfalfa cultivars at salinity level of15 dS/m (᭛) and 25 dS/m (᭡) (arrow indicates day of salinization).
between cumulative biomass accumulation of the forages and days after salinization (r20.84–0.99). The larger the slope difference of the relationships between the 15 dS/m treat-ment and the 25 dS/m treatments, the more sensitive the crop is to salinity. With the exceptionof bermudagrass, which increased yield at higher level of salinity, and big trefoil, whichfailed to establish at the higher level of salinity, ranking of forages according to the percentreduction in biomass yield due to higher level of salinity of the irrigation water was in order;Salado alfalfa (54%) = SW 9720 alfalfa (52%) > Duncan Paspalum (41%) > narrow leaftrefoil (30%) > alkali sacaton (24%) > Polo Paspalum (16%) > Jose tall wheatgrass (11%)= kikuyugrass (11%). Although there was a significant reduction in yield due to the higherlevel of salinity in the irrigation water, except bermudagrass, all forage species except bigtrefoil were able to establish, survive, and accumulate considerable amounts of biomass.
At higher levels of salinity, forage species ranked in the order: bermudagrass (10.7 t/ha) P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 Alkali sacaton
Cumulative biomass yield (kg DM /ha)
Days after planting
Cumulative biomass yield (kg DM /ha)
Days after planting
Fig. 2. Cumulative forage biomass in relation to days after planting and days after planting for alkali sacaton andBermuda grass at salinity level of 15 dS/m (᭛) and 25 dS/m (᭡) (arrow indicates day of salinization).
= Duncan Paspalum (10.5 t/ha) > kikuyugrass (8.8 t/ha) > Polo Paspalum (7.8 t/ha) > Josetall wheatgrass (6.6 t/ha) > narrow leaf trefoil (5.9 t/ha) = alkali sacaton (5.6 t/ha) = SWalfalfa (5.6 t/ha) > Salado alfalfa (4.6 t/ha).
The potential nutritive value of the forages was evaluated based on their content of organic matter, neutral detergent fiber, in vitro (at 30 h) digestible NDF (dNDF), in vitro (at 30 h)true digestibility of dry matter (IVTD) and in vitro (at 24 h) gas evolution. The NDF isan estimate of the cell wall minus pectin and the dNDF is an estimate of the NDF that isdigestible in cows at low level of production. Gas evolution at 24 h in vitro estimates itsdigestion when fed to cows at a maintenance level of production and is used to estimate P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 Cumulative biomass yield (kg DM /ha)
Days after planting
Kikuyugrass
Cumulative biomass yield (kg DM /ha)
Days after planting
Fig. 3. Cumulative forage biomass in relation to days after planting for Jose tall wheat and Kikuyugrass at salinitylevel of 15 ds/m (᭛) and 25 ds/m (᭡) (arrow indicates day of salinization).
energy value at a maintenance level of energy intake. In general the quality, or energy value,of the forage increases as: OM increases, NDF decreases, dNDF increases, IVTD increasesand/or gas production increases. All forage quality parameters for each of the three cuttingssignificantly differed among species tested (P < 0.001). However, salinity had differentialeffects depending upon the species, forage quality parameter and harvest date.
At the first cutting, the OM content of bermudagrass was higher at 25 dS/m than at 15 dS/m, but the reverse was true for big trefoil (P < 0.05; The NDF levels ofSalado alfalfa, big trefoil and Jose tall wheatgrass were lower (P < 0.05) when grownat 25 dS/m versus 15 dS/m, but the opposite was true for Bermuda grass (P < 0.05).
Digestibility of NDF (i.e. dNDF) and the in vitro digestibility of DM (IVTD) were notinfluenced by salinity. However gas production, an indicator of the energy value of theforage, was higher (P < 0.05) in Jose tall wheatgrass and kikuyugrass at 25 dS/m versusbiomass from the 15 dS/m treatment. The overall metabolizable energy for the forages was P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 Cumulative biomass yield (kg DM /ha)
Days after planting
Cumulative biomass yield (kg DM /ha)
Days after planting
Fig. 4. Cumulative forage biomass in relation to days after planting for Paspalum cultivars at salinity level of15 ds/m (᭛) and 25 ds/m (᭡) (arrow indicates days of salinization).
not influenced by salinity, except in Jose tall wheatgrass where higher salinity increased theME value.
In the third cutting, higher salinity generally increased OM content (P < 0.01) and reduced NDF (P < 0.001; Increased salinity tended to decrease fat (EE) content(P < 0.05) but this effect was slight. Other nutritive descriptors were not influenced bysalinity of the applied water, except in Salado alfalfa where increased salinity increased theME (P < 0.05).
For the fifth harvest, increased salinity increased the OM and CP content of the forages (P < 0.05; The NDF content of SW 9720 alfalfa was lower (P < 0.05), and thegas production was higher (P < 0.05), at 25 dS/m than at 15 dS/m. This resulted in a higher(P < 0.05) ME in SW 9720 alfalfa grown at the higher salinity level. NDF digestibility and Table 2Effect of salinity level on nutritive value of different species of forages at first cut OM: organic matter; CP: crude protein; EE: ether extract; NDF: neutral detergent fiber. Means with different letters between salinity levels within species differ (P < 0.05). NS:not significant.
a IVTD: in vitro true digestibility (proportion of dry matter incubated).
b dNDF: digestible fiber (proportion of fiber incubated); ME: metabolizable energy.
∗∗∗ P < 0.001.
Table 3Effect of salinity level on nutritive value of different species of forages at third cut OM: organic matter; CP: crude protein; EE: ether extract; NDF: neutral detergent fiber. Means with different letters between salinity levels within species differ. NS: not significant.
a IVTD in vitro true digestibility (proportion of dry matter incubated).
b dNDF, digestible fiber (proportion of fiber incubated); ME: metabolizable energy.
∗ P < 0.05.
∗∗∗ P < 0.001.
Table 4Effect of salinity level on nutritive value of different species of forages at fifth cut OM: organic matter; CP: crude protein; EE: ether extract; NDF: neutral detergent fiber. Means with different letters between salinity levels within species differ. NS: not significant.
a IVTD in vitro true digestibility (proportion of dry matter incubated).
b dNDF, digestible fiber (proportion of fiber incubated); ME: metabolizable energy.
∗ P < 0.05.
∗∗∗ P < 0.001.
P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 Cumulative biomass yield (kg DM /ha)
Days after planting
Cumulative biomass yield (kg DM /ha)
Days after planting
Fig. 5. Cumulative forage biomass in relation to days after planting for the trefoil cultivars at salinity level of15 ds/m (᭛) and 25 ds/m (᭡) (arrow indicates day of salinization.) IVTD were not influenced by the salinity of applied water. Salinity influenced various foragequality parameters, including NDF, OM, gas production and CP, but their significance variedamong species and cuttings. However, whenever higher salinity significantly influencedthese quality parameters, it did so positively except for NDF in Bermuda grass and OM inBig trefoil in first cutting biomass.
4. Discussion
The forages varied considerably in their overall tolerance to salinity. Based on relative differences in the slopes of the cumulative biomass functions at 15 and 25 dS/m, big trefoil P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 was the most sensitive to salinity followed by the alfalfa cultivars. Duncan Paspalum wasthe next most sensitive to salinity followed by narrow leaf trefoil, alkali sacaton and PoloPaspalum. Exhibiting the highest salt-tolerance were bermudagrass, kikuyugrass, and Josetall wheatgrass. Although salt-tolerance ratings are not available in the literature for allthese species, these rankings are in general agreement for those where data are available( The forages varied dramatically in DM biomass accumulation potential under moderate (15 dS/m) and high (25 dS/m) salinity. Under moderate salinity conditions, the alfalfa cul-tivars produced substantial amounts of biomass. However as salinity increased to 25 dS/m,biomass was substantially reduced while the more salt-tolerant cultivars were little affected.
For example kikuyugrass, one of the most tolerant species tested, produced more biomassat the higher salinity at any period after salinization. This suggests that the actual foragespecies preference in saline drainage water reuse systems will be dependent upon the salin-ity of the water being reused, as well as management practices that affect salinity in thecrop root zone.
It is also important to emphasize that these production functions reflect production poten- tials when the average root zone salinity of the soil water is 15 or 25 dS/m. If it is assumed thatsoil water salinity is about twice that of the saturated soil extract (an expression most frequently used among plant and soil scientists, corresponding averageroot zone salinities would be 7.5 and 12.5 dS/m. Since soil salinities in reuse systems in theSan Joaquin Valley can exceed 12.5 dS/m, caution is advised in selecting cultivars whosebiomass was reduced substantially as salinity increased (i.e. big trefoil and the alfalfas).
Plants growing in a saline and/or sodic environment may face growth limitations, par- ticularly in terms of root establishment and biomass yield. Soluble salts in either irrigationwater or in soil can be toxic to plants grown in such situations Re-duction in biomass yield due to higher level of salinity observed in the current study, is inagreement with Measurable effects ofsoil salinity on plants can include poor root development and reduced root growth, henceleading to reduction in biomass accumulation (Plant species ableto colonize salt-affected soils are important for stabilization and reclamation of degradedland. The ability of some plant species to grow under a wide range of stress conditions hasgreatly increased their adaptability. compared different cultivars ofalfalfa and reported a biomass accumulation decrease due to higher level of saline irrigationwater, but no difference among cultivars in salt-tolerance.
The CP content of the alfalfa cultivars was higher than those reported by and the ME content and gas production of our alfalfa cultivars were higher thanthose of The higher CP and lower NDF contents of the tropicalspecies kikuyugrass and bermudagrass in this study, compared to those reported of could be due to the stage of maturity of plants at harvest, as maturity is one ofthe major factors influencing forage quality. For example, a reduction in CP from 36.1 to 19.4%, and an increase in NDF from 18.6 to 42.6%, fromearly to late harvest in alfalfa.
P.H. Robinson et al. / Animal Feed Science and Technology 111 (2004) 175–189 The increase in OM content of forages in the third and fifth cutting due to increased level of salinity was similar to that reported by While the effect ofsalinity on CP content of forages in the current study was not consistent, higher levels ofsalinity did increase the CP content of forages in the first and fifth cuttings, a finding that isconsistent with The significant interaction between level of salinity and forage species on chemical composition and in vitro digestibility parameters indicates that considerable variation existsamong species in metabolic response to the level of salinity of irrigation water. Overall, thelevel of salinity had little effect on IVTD, dNDF, gas production and the estimated MEvalue of these forages. However the general decrease in NDF with the higher salinity levelof the irrigation water is consistent with NDF content ofryegrass was reduced, and in vitro digestibility was increased, due to irrigation with salinewaters.
5. Conclusions
The forage species performed differently in terms of biomass accumulation and forage quality parameters relative to the salinity level of the applied irrigation water. Bermuda-grass, Jose tall wheatgrass and Duncan Paspalum emerged as favorites based on combinedattributes related to salt-tolerance, absolute biomass accumulation at high salinity and over-all forage quality. Kikuyugrass, which had the third highest biomass accumulation, wasjudged to be unacceptable due to its poor nutritional quality. Although narrow leaf trefoilhad a relatively high nutritional quality, its biomass accumulation potential was judged tobe unacceptable. Alfalfa cultivars were found to be the most sensitive to the higher level ofsalinity of irrigation water relative to biomass accumulation.
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