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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 4, Num. 4, 1996, pp. 433-440
African Crop Science Journal,
Vol. 4. No. 4, pp. 433-440, 1996

Effects of furrow diking and tillage on water storage, plant water use efficiency and yield of sorghum

A.A. SOW, L.R. HOSSNER^1, P.W. UNGER^2 and B.A. STEWART^3

Institut d'Economie Rurale (IER), B.P. 258 Bamako, Mali
^1 Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843
^2 USDA-ARS, P.O. Drawer 10, Bushland, Texas 79012
^3 Dryland Agriculture Institute, West Texas A&M University, P.O. Box 278, Canyon, Texas 79016-0001

(Received 25 March, 1996; accepted 28 August, 1996)


Code Number: CS96084
Sizes of Files:
    Text: 30.3K
    Graphics: No associated graphics files    

ABSTRACT

In water deficit areas, like the Texas Northern High Plains, cultural practices are needed to reduce runoff and capture rain water. Studies were conducted at Bushland, Texas, on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) to improve water storage, sorghum (Sorghum bicolor (L.) Moench) water use efficiency, and grain yield. Treatments were conventional tillage plus furrow diking (FD), conventional tillage (CT), no-tillage with wheat Triticum aestivum residue maintained on the plots (NT+) and no-tillage with wheat residue removed (NT-). The FD and NT+ treatments were more effective than CT and NT treatments for improving precipitation storage by reducing and even preventing runoff and increasing infiltration. The more efficient use of soil water with the FD and NT+ treatments were reflected in greater sorghum grain yield. Average grain yield with the FD treatment was 4840 kg ha^-1, which was about 800 kg ha^-1 more than with the CT and NT-treatments. Grain yield with the NT+ treatment was 15 % greater than with the CT and 17% greater than with the NT-treatment.

Key Words: Furrow diking, conventional tillage, no-tillage, water use efficiency

RESUME

Dans les zones deficitaires en eau do sol comme les Hautes Plaines du Nord du Texas, les pratiques culturales sont necessaires pour reduire le ruissellement et retenir les eaux de pluie. Des etudes ont ete conduites a Bushland, Texas, sur un sol Pullman argileux-limoneux (fine, mixed, thermic Torrertic Paleustoll) pour ameliorer la teneur en eau du sol, l'utilisation efficace en eau du sorgho [Sorghum bicolor (L.) Moench] et les rendements. Les traitements etaient le labour conventionel plus les billions cloisonnes (FD), le labour conventionel (CT), sans labour avec le maintien des residus du ble (Triticum aestivum) sur les parcelles (NT+), et sans labour et sans residus de ble (NT-). Les traitements FD et NT+ se sont montres plus efficaces que les traitements CT et NT pour l'amelioration du stockage des pluies en dimuant et meme en controlant le ruissellement et en ameliorant I 'infiltration. L 'utilisation la plus efficace en eau du sol avec les traitements FD et NT+ sest traduite par des rendements plus eleves du sorgho. Le rendement moyen en grain avec le traitement FD etait de 4840 kg par hectare, qui etait de 800 kg par hectare plus que le rendement des traitements CT et NT-. Le rendement grain du traitement NT+ etait 15 % superieur a celui du CT et 17% superieur acelui du traitement NT-.

Mots Cles: Billions cloisonnes, culture conventionelle, sans culture, utilisation efficace d'eau.

INTRODUCTION

Limited and erratic rainfall in the Texas Northern High Plains often results in low crop yields and sometimes in total crop failures. Practices that conserve water received as rainfall can greatly improve the potential for success in many dryland cropping systems.

Management of crop residues to retain them on the soil surface has generally increased water conservation. Unger and Stewart (1983) reported that cultural practices such as water harvesting, fallowing, ploughing or mulching many increase the amount of water that is available to a crop. Furrow dikes, which are small dikes in furrows at about 3-m intervals throughout the length of the field, can increase crop yields and control erosion (Clark and Jones, 1980). Such dikes retain and distribute potential runoff water on the surface, thus allowing it to infiltrate. For a 2 year study with continuous sorghum at Etter, Texas, conservation of runoff with furrow diking resulted in a yield increase (Stewart et al., 1985). Gerard et al. (1984) found that placing a dike every 16.5 m in the furrow increased sorghum yields by 11 to 17% in 1979 in the Texas Rolling Plains. Furrow diking increased cotton yields by about 35% in 1981 (Clark, 1983).

Unger and Wiese (1979) obtained greater water storage and sorghum yields in their study with no-tillage compared to other tillage treatments on the Pullman soil at Bushland, Texas. The no-tillage system can provide not only protection against short duration drought by contributing to more efficient water use, but also help control erosion during severe storms. In another study at Bushland (Unger, 1984), both water storage and average sorghum yields were greatest with the no-tillage treatment. Also, Gerik and Morrison (1984) obtained similar soil water storage and grain yield of sorghum by using no-tillage and conventional tillage treatments on a Mollisol (Austin series) at Temple, Texas.

In the Texas Northern High Plains the water use efficiency, which represents the units of grain produced per unit of water used by the crop, is low. Unger (1978) reported that water use efficiency in a dryland cropping system can be doubled or even tripled if producers adopt dryland conservation technologies. Efficient use of rainfall requires that 1) a maximal amount of water be available to the crop, and 2) the crop uses the available water as efficiently as possible to produce desirable biomass.

In a semiarid environment, efficient management and more effective use of precipitation are necessary for intensifying crop production. The purpose of this study was to investigate management systems which can decrease runoff, improve soil water storage, plant water use efficiency and increase grain yield.

MATERIALS AND METHODS

The experiment was conducted at the USDAARS Conservation and Production Research Laboratory, Bushland, Texas. Bushland is in the semiarid portion of the Texas High Plains (35" 11' N, 102" 5' W). Annual precipitation average 470 mm. Conservation tillage and crop residue management systems have been used for the last 10 to 35 years. The study was conducted on fields in a wheat-sorghum-fallow (WSF) rotation. The soil was Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll), which is moderately deep and well drained with 1% slope. Selected surface soil physical and chemical properties are shown in Table 1. Four treatments were involved in the study: (1) Furrow diking (FD): disked twice, sweep ploughed once and diked between every row. Dikes were 0.15 to 0.20 m high and were installed in each furrow at a spacing of 3-m with a six row commercial diker; (2) Conventional tillage (CT): disked twice, sweep ploughed once; (3) No-tillage with wheat residue (NT+) maintained in the fields; and (4) No-tillage with wheat residue removed from the field (NT-) prior to seeding. Wheat residues were incorporated during tillage operation. Treatments were imposed 2 weeks prior to seeding of grain sorghum (Dekalb 'DK-46'). Treatments were replicated three times in a randomised complete block. Each plot was 40-m long and 5-m wide (6 rows of grain sorghum).

TABLE 1. Selected physical and chemical properties in the surface 0.15 m of Pullman clay loam at Bushland, TX

--------------------------------
Property         Value
--------------------------------
Physical 
Sand            13.7% 
Silt            39.9% 
Clay            46.4%

Chemical 
pH H2O (1:2)     7.2 
pH-KCl           6.7 
Organic matter  20.6 g kg^-1 
CEC^a           39.5 cmol kg^-1

^a CEC = Cation Exchange Capacity
---------------------------------

The weed control programme for the WSF system was as follows: (i) 3.36 kg ha^-1 atrazine [2 chloro-4-(ethylamino)-6-(isoprophlamino) triazine] and 0.84 kg ha^-1 2,4-D [(2,4-dichlorophenoxy) acetic acid] applied immediately after wheat harvest; (ii) terbutryn [2-tert-butylamino)- 4-(ethylamino)-6-(methylthio)-s-triazine] was applied at a rate of 3.40 kg ha^-1 to all plots before planting sorghum for additional weed control during the growing season. The herbicide was incorporated during tillage operations on FD and CT plots, but was not incorporated on NT+ and NT- plots. No fertilizer was applied because dryland crops on Pullman clay loam at Bushland have not responded to applied fertilizers (Eck and Jones, 1992). On no-tillage plots, the only soil disturbance was that involved in seeding the sorghum. Each plot was bordered on all sides by earthen ridges.

Soil water content was monitored by the neutron scattering technique at three random locations per plot to a 1.8-m depth at 30-cm depth increments starting at the 30-cm depth. The measurements were performed at about 2 weeks intervals during the sorghum growing season. Measurements were made using 32-s count integration with a neutron probe and scaler rate meter. Runoff was measured with H-flumes and water stage recorders.

Grain sorghum plants on 3 linear m of the four central rows were cut at ground level in each plot. Wet bundle weights were adjusted to dry matter production from representative subsamples taken from the bundle and dried 3 days at 60 C in forced air ovens. Grain yields were determined on ten meters of the four central rows by hand harvesting. The panicles were oven-dried at 60 C for 3 days, then weighed and threshed in a stationary sample thresher. Grain was weighed and adjusted to 135 % moisture to obtain net grain weight.

Ten plants were harvested flush with the ground surface in each plot. Panicles were harvested at the base of the lowest grain branch. Each plant was dried separately at 60 C for 3 to 4 days and dry matter yields and grain yields of individual plants were determined for computing HI (harvest index defined as the ratio of grain to total dry matter). The HI values were computed as the ratio of the grain yield to dry matter yield per plant in the respective treatments.

Data were analysed to determine significant statistical differences using the analysis of variance procedure. Duncan Multiple Range Test was used to test mean differences at the 0.05 probability level.

RESULTS AND DISCUSSION

Total rainfall from 1 June to 10 October was near the long-term average in 1991, and above the long-term average In 1992 (Table 2). In each growing season, however, there were periods of below and above average rainfall. Rainfall in 1991 was below average early in the season (May), considerably above average during June and July, and below average during August, September and October. Rainfall in 1992 was above average from May until August, below average during September, and near average during October.

TABLE 2. Long-term average and growing season rainfall (mm)in 1991 and 1992 at Bushland, Texas

-----------------------------------------------
Month                Precipation
            -----------------------------------
            1991   1992   20-yr avg   50-yr avg
-----------------------------------------------
May^+        64     76       69         69 
June         90    182       69         75 
July         83     73       56         63 
August       60     96       81         71 
September    28     15       61         49 
October      27     41       37         42 
Total       352    483      373        369
^+ Planting dates were 10 June in 1991 and 1992.
Total growing season rainfall was 259 mm in 1991 and 325 mm in 1992.
-------------------------------------------------------------------------

Available soil water at sorghum planting (Table 3) consisted of water in the soil at wheat harvest and that stored during fallow (330 days from wheat harvest to planting of grain sorghum). The FD and NT+ treatments had significantly increased available water contents at sorghum planting in 1992 and the amounts approached field capacity (230 mm) for the 1.8m depth. These water contents show that these two treatments resulted in almost complete filling of the storage reservoir of Pullman clay loam to the 1.8 m depth (Unger and Pringle, 1981). Furrow diking resulted in about 30 mm more available water than CT and NT- treatments in 1991, while the NT+ resulted in 35 mm more water than CT and NT- treatments. Similar results were reported by Gerard et al. (1984) and Unger (1990) on the effectiveness of diking and no-till with residue maintained in the field in increasing water storage.

TABLE 3. Plant available soil water content (mm) to the 1.8 m depth at planting and harvest, and net soil water use under different management systems in 1991 and 1992 at Bushland,Texas

-----------------------------------------------------
YEARS                Management systems*
       ----------------------------------------------
                    FD       CT       NT+      NT-
-----------------------------------------------------
Water at planting 
1991               169 a    140 b    174 a    138 b 
1992               222 a    164 b    214 a    165 b 
Average            195 a    152 b    194 a    152 b

Water at harvest 
1991                44 a     29 b     41 a     26 b 
1992                74 a     51 b     70 a     49 b 
Average             59 a     40 b     55 a     38 b

Net soil water use 
1991               125 a    111 b    132 a    112 b 
1992               148 a    113 b    145 a    116 b 
Average            136 a    112 b    139 a    114 b
* Management systems were: Furrow diking (FD); Conventional tillage (CT); No-tillage with standing wheat residue (NT+); and No tillage without residue (NT-).

Means within each row followed by different letters are significantly different at the 0.05 level according to the Duncan Multiple Range test.
---------------------------------------------------------------------------

Trends in available soil water at sorghum harvest, based on water retained in soil above a matric potential of -1.5 MPa, followed available soil water at sorghum planting (Table 3). Plant available soil water at sorghum harvest was greater with the FD and NT+ treatments than with the CT and NT- treatments. This indicated that sufficient plant available water was left in FD and NT+ treatments and grain sorghum did not utilise all the soil profile water.

Net soil water use (measured as the difference in soil water at planting and at harvest) differed significantly among management systems (Table 3). The difference between FD and NT+ treatments was small in both years. This small difference in net soil water use resulted from the effectiveness of these two management systems in capturing rainstorm and allowing it to infiltrate into the soil. Thus, greater infiltration of water occurred in these plots during the growing seasons. The difference between CT and NT- treatments also was small.

Furrow diking and NT+ effectively captured rainfall and reduced runoff volume in both years (Table 4). Average runoff with the FD and NT+ treatments during the two crop seasons was 4 and 9 mm, respectively. Runoff was 18 mm from CT plot and 31 mm from NT- plot. Total growing season precipitation was 292 mm. The FD and NT+ treatments prevented most runoff and resulted in greater infiltration. Water infiltration in 1991 in the FD and NT+ plots was 6 and 5% greater than in the CT plot; and 11 and 9% greater than in the NT- plot. Water infiltration in 1992 in the FD and NT+ plots was 4 and 2% greater than in the CT plot; and 10 and 8% greater than in the NT plot (Table 4). The dikes in the FD treatment trapped runoff and allowed it to inflitrate into the soil. Residue from the previous wheat crop in the NT+ treatment reduced runoff. Early in the season, when plots were not covered by a complete canopy, runoff from the bare soil surface caused much lower soil water contents in the CT and NT treatments when compared with the FD and NT+ treatments. Similar results were reported by Stewart et al. (1985), who stated that furrow dikes conserved 68 and 88 mm of potential runoff in 1980 and 1981, respectively.

TABLE 4. Runoff (mm) and infiltration (mm) under different management systems in 1991 and 1992 at Bushland, Texas

--------------------------------------------------------------------------
Years  Rainfall events  Growing           Management system* 
          producing     season   ----------------------------------------- 
           runoff      rainfall       FD       CT        NT+      NT-
--------------------------------------------------------------------------
Runoff#  
1991         6           259           1 c     16 b       5 c     27 a 
1992        10           325           7 d     21 b      13 c     36 a 
Average      8           292           4 d     18 b       9 c     31 a

Infiltration# 
1991                                 258 a    243 b     254 a    232 c 
1992                                 318 a    304 c     312 b    289 d 
Average                              288 a    274 c     283 b    261 d
* Management systems were: Furrow diking (FD); Conventional tillage (CT); No-tillage with standing wheat residue (NT+); and No-tillage without residue (NT-).
Means within each row followed by different letters are significantly different at the 0.05 level according to the Duncan Multiple Range test.
# Based on difference between growing season precipation and runoff. Rainfall during the growing season was 259 and 325 mm in 1991 and 1992, respectively.
---------------------------------------------------------------------------

Greater than average rainfall from May through August in 1992 (Table 2) was responsible for grain yield that varied from 4160-5000 kg ha^-1. The increases in grain yield due to furrow diking were 20 and 18% in 1991 and 1992 compared to the CT treatment; and 21 and 20% in 1991 and 1992 compared to the NT- treatment. The NT+ produced 720 kg ha^-1 more grain in 1991 and 600 kg ha^-1 more grain in 1992 than the NT- treatment. The additional water stored in soil due to NT+ treatment over the CT and NT- treatments was responsible for the increased sorghum grain yield. Similar results were reported by Unger and Wiese (1979).

Stover production was not influenced by the four contrasting management methods (Table 5). A plausible explanation for differences in grain production when compared to stover production is related to differences in plant available water. Sorghum plants on CT and NT- plots suffered from water stress during the late part of the growing season, which significantly reduced panicle development and grain filling. The increased available water stored for use by FD and NT+ treatments resulted in greater total dry matter production (Table 5). Averages across 2 years showed that FD increased total sorghum biomass yields by 700, 190, and 710 kg ha^-1 over those with CT, NT+, and NT-treatments.

TABLE 5. Effect of different management systems on grain sorghum yields (kg ha^-1) and harvest index in 1991 and 1992 at Bushland, Texas

-------------------------------------------------
Year                  Management systems*
          ---------------------------------------
              FD        CT       NT+       NT-
------------------------------------------------
Grain yield 
1991        4680 a    3900 b    4620 a    3880 b 
1992        5000 a    4240 c    4760 b    4160 d 
Average     4840 a    4070 c    4690 b    4020 c

Stover yield 
1991        5070 a    5170 a    5180 a    5200 a 
1992        5190 a    5230 a    5000 a    5270 a 
Average     5130 a    5200 a    5090 a    5240 a

Total dry matter 
1991        9750 a    9070 b    9800 a    9080 b 
1992       10180 a    9470 b    9750 ab   9430 b 
Average     9970 a    9270 b    9780 a    9260 b

Harvest index (HI)# 
1991        0.48 a    0.43 b    0.47 a    0.43 b 
1992        0.49 a    0.45 b    0.49 a    0.44 b 
Average     0.49      0.44      0.48      0.43
  
* Management systems were: Furrow diking (FD); Conventional tillage (CT); No-tillage with standing wheat residue (NT+); and No-tillage without residue (NT-).
Means within each row followed by different letters are significantly different at the 0.05 level according to the Duncan Multiple Range test.
# Ratio of grain to total dry matter yields.
--------------------------------------------------------------------------- -

The greater soil water content in FD and NT+ plots resulted in greater harvest index (HI) when compared to the CT and NT- treatments (Table 5). Lower plant available water due to runoff enhanced early season depletion of soil water in the CT and NT- plots and resulted in reduced soil water content by midseason. This increased the probability of water stress occurring late in the season, which reduced HI and decreased grain yield of these treatments compared to the FD and NT+ treatments.

Differences in seasonal water use were determined by the difference in soil water contents at planting and at harvest, and to changes in soil water content during the growing seasons (Table 6). Furrow diking and NT+ treatments resulted in similar total water use in both years. Even though water use was greater from FD and NT+ plots, water content in these plots remained higher throughout most of the season. Because of this, sorghum in FD and NT+ plots experienced less water stress, responded more to limited rainfall and yielded more than sorghum in CT and NT plots.

TABLE 6. Total water use by sorghum (mm) and water use efficiency (WUE) (kg ha^-1 mm^-1) for grain, stover, and total dry matter production under different management systems in 1991 and 1992 at Bushland, Texas

------------------------------------------------------
Year                     Management system*
              ----------------------------------------
                  FD         CT       NT+      NT
------------------------------------------------------
Total growing season water use 
1991             383 a      354 b    388 a    356 b    
1992             465 a      417 c    456 a    405. b    
Average          424 a      386 b    422 a    375 b    
                               
WUE for grain production        
1991            12.2 a     11.0 b    11.9 ab   11.3 b  
1992            10.7 a     10.2 b    10.4 ab   10.3 ab   
Average         11.5 a     10.6 c    11.2 b    10.8 c   
                               
WUE for stover production      
1991            13.3 c     14.6 ab   13.4 bc   15.1 a  
1992            11.2 bc    12.6 ab   10.9 c    13.0 a
Average         12.3 b     13.6 a    12.2 b    14.1 a

WUE for total dry matter production
1991            25.3 a     25.6 a    25.5 a    26.4 a
1992            21.9 a     22.7 a    21.4 a    23.4 a
Average         23.6 a     24.2 a    23.5 a    24.8 a
* Management systems were: Furrow diking (FD) Conventional tillage (CT); No-tillage with standing wheat residue (NT+); and No-tillage without residue (NT-).
# Total water use includes net soil water use and total rainfall from planting to harvest. Rainfall was 259 and 325 mm in 1991 and 1992, respectively.
Means within each row followed by different letters are significantly different at the 0.05 level according to the Duncan Multiple Range test. Based on grain yield and total water use.
--------------------------------------------------------------------------

Trends in water use efficiency (WUE), based on kg of grain or stover produced per ha mm^-1 of water used, generally followed grain or stover yield trends (Table 6). Average WUE values for grain production increased from 10.6 kg ha^-1 mm^-1 with CT to 11.5 kg ha^-1 mm^-1 with FD treatment. Average WUE values increased from 10.8 kg ha^-1 mm^-1 with NT- to 11.0 kg with NT+ treatment. The different responses in WUE for grain production due to the four treatments suggested that some additional growth occurred on the FD and NT+ plots. Additional plant available water on FD and NT+ plots reduced plant water stress and permitted greater precipitation use during critical booting, flowering and grain filling stages, which improved grain yields. The FD and NT+ treatments were very effective in reducing runoff and increasing water infiltration into the soil, thus, resulting in greater grain yields. Consequently, these two systems resulted in greater WUE values.

Treatment values for WUE were larger for stover than for grain (Table 6). The much higher WUE for stover than for grain indicated that grain filling was hindered for CT and NT- compared with the FD and NT+ treatments. This was indicated by the low grain yield with CT and NT treatments (Table 5). Water use efficiency for total dry matter production was higher in 1991 than in 1992 for all treatments. The difference among treatments were not significant within a given year.

CONCLUSION

The decrease in runoff and the greater ability to store water under the FD and NT+ treatment conditions produced a greater water reserve. This water reserve carried grain sorghum through periods of short-term drought and avoided the development of detrimental plant water stress. The FD and NT+ production systems resulted in an average increase in grain yield of about 750 and 650 kg ha^-1 over the CT and NT- through conservation of soil water. The study shows that FD and NT+ management systems increase the growth and yield of grain sorghum compared to the CT and NT- management systems. The Texas Agriculture Statistics Service (1993) reported that 233,000 ha of sorghum were produced in the Texas Northern High Plains (19.2% of the total harvested sorghum in Texas). An additional 750 or 650 kg ha^-1 due to FD or NT+ systems would increase annual sorghum grain production by approximately 162 million kg compared to the CT system. In water deficit areas, like the Texas Northern High Plains, the water conserved with FD and NT+ systems can result in greater crop yields; thus increasing financial returns for the region without additional costs for seed, fertilizer, or water. This sizable increase in the region's economy can occur simply by more efficient use of existing climatic resources.

ACKNOWLEDGMENTS

The work reported in this paper was supported by Texas A & M University (Soil & Crop Sciences Department), USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas and the Soil Management Collaborative Research Support Program (USAID No. DAN-1311-GSS-6018-00). These institutions are greatly acknowledged.

(The mention of trade or manufacturer names is made for information only and does not imply an endorsement, recommendation, or exclusion by USDA- Agricultural Research Service. Mention of a pesticide does not constitute a recommendation for use nor does it imply registrion under FIFRA as amended.)

REFERENCES

Clark, L.E. 1983. Response of cotton to cultural practices. Texas Agricultural Experimental Station PR-4175. College Station, Texas, USA.

Clark, R.N. and Jones, O.R. 1980. Furrow dams for conserving rainwater in a semiarid climate. In: Proceeding Crop Production Conservation in the 80s. pp. 198-206. American Society of Agricultural Engineering. St. Joseph, Michigan, USA.

Eck,,H.V. and Jones, O.R. 1992. Soil nitrogen status as affected by tillage, crops, and crop sequences. Agronomy Journal 84:660-668.

Gerard, C.J.. Sexton. PD. and Conover, D.M. 1984. Effect of furrow diking, subsoiling, and slope position on crop yields. Agronomy Journal 76:945-950.

Gerik, T.J. and Morrison, J.E., Jr. 1984. No-tillage of grain sorghum on a swelling clay soil. Agronomy Journal 76:71-76.

Stewart, B .A., Unger, P.W. and Jones, O.R. 1985. Soil and water conservation in semiarid regions. In: Soil Erosion and Conservation. El-Swaify, S.A., Moldenhauer, W.C. and Andrew Lo (Eds.), pp. 328-337. Soil Conservation Society of America, Ankeny, IA.

Unger, P.W. 1978. Straw-mulch rate effect on soil water storage and sorghum yield. Sail Science Society of America Journal 42:485491.

Unger, P.W. 1984. Tillage and residue effects on wheat, sorghum, and sunflower grown in rotation. Soil Science Society of America Journal 48:885-891.

Unger, P.W. 1990. Conservation tillage systems. Advances in Soil Science 13:27-61.

Unger, P.W. and Pringle, F.B. 1981. Pullman soils: distribution, importance, variability and management. The Texas Agricultural Experiment Station. B- 1372. College Station, Texas, USA.

Unger, P.W. and Stewart, B.A. 1983. Soil management for efficient water use: An overview. In: Limitations to Efficient Water Use in Crop Production. Taylor, H .M., Jordan, W.R. and Sinclair, T.R. (Eds.), pp. 419-460. ASA, CSSA, and SSSA, Madison, Wisconsin, USA.

Unger, P.W. and Wiese, A.F. 1979. Managing irrigated winter wheat for water storage and subsequent dryland grain sorghum production. Soil Science Society of America Journal 43:582-588.

Copyright 1996 The African Crop Science Society

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