Wind, G.P.

English

Name not available

Workability and drainage

Wageningen Yield 

NN31545.0890 D T A 8 9 ° november 1975 
Instituut voor Cultuurtechniek en Waterhuishouding 
Wageningen 
WORKABILITY AND DRAINAGE 
i r . G. P . Wind 
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C O N T E N T S 
page 
INTRODUCTION 1 
METHOD 2 
RESULTS 2 
APPLICATION 3 
LITERATURE 5 
FIGURES 1-7 
INTRODUCTION 
Fer t i l i ty of a soil , both physical and chemical , is cer ta in ly an 
impor tant factor in determining suitabili ty for agr icu l tu re . For 
modern agr icul ture the workabili ty is a l ready important and i ts s ig -
nificance is s t i l l growing. In the beginning of this century land p r i ce s 
of the fer t i le , poorly workable clay soi ls were twice those of the in-
fer t i le , well workable sandy so i l s . Today one can buy two ha clay 
soil for the selling pr ice of one ha sandy soil in the Nether lands . 
Workability has been investigated l e s s than fert i l i ty. Workability 
is affected by a la rge number of fac tors , e. g. dra inage , s t r u c t u r e , 
soil profile, preceding c rop . But the mos t important factor govern-
ing workabili ty is wheather . Its influence is so big that one cannot 
succesfully study the effect of other factors if not the influence of 
wheather is investigated f i rs t . This has seldom been done because 
of two r ea sons : f irst ly it was impossible to calculate mois tu re con-
ditions of the topsoil from wheather data; secondly it is i m p r a c t i c a l 
r e s e a r c h , for the wheather cannot be control led. 
Now that dynamic models a re available of the unsa tura ted flow 
of m o i s t u r e , the f i rs t reason has fallen away. It is now possible to 
calculate mois ture condition, and thus workabil i ty, over a la rge 
number of y e a r s . And so it has become possible to investigate the 
effect of many factors on workabil i ty, with na tura l or s tandardized 
wheather conditions. 
This paper d i scusses the effect of draindepth and drainage in -
tensi ty on workabili ty of a loamsoi l in spr ing . Fo r the investigation 
na tu ra l wheather conditions were used, and it s eems now, that such 
r e s e a r c h is cer ta in ly not total ly imprac t i ca l . 
METHOD 
Mois ture tension in the top 5 cm was calculated during 23 y e a r s 
in the months January to the end of Apri l , 5 t imes per day. T h e r e -
fore an analog model of WIND (1972) was used and two numer ica l 
models of VAN KEULEN and VAN BEEK (1971) and of WIND and 
VAN DOORNE (197 5). 
These models can calculate the mois tu re condition at every depth 
and t ime by combination of the s torage function (moisture c h a r a c t e -
r i s t i c ) and the t r anspor t function of the unsa tura ted soil with the 
drainage function. The la t te r is expressed in depth and intensity. 
The initial condition at January first was found by a rough ca l -
culation over the preceding eight months . The daily ra infal l - and 
evaporation data of the meteorological station in De Bilt were used 
of each of the yea r s between 1951 and 1973. 
A descr ipt ion of the application of the mode ls , the problems 
ar i s ing and their solution will be published by WIND, ear ly in 197 6 
in Nether lands Journal of Agr icul tura l Science. 
The calculations could be checked by observat ions in all 23 ye a r s 
on the exper imenta l f a rm Wes tmaas , fig. 1. The soil used is a loam 
soil , thought to be homogeneous, containing 25% clay. 
The soil was cons idered as workable for planting when the top 
5 cm had a mois ture tension of -100 cm for grains and of -300 cm 
for potatoes and sugarbeets or when it was d r i e r than these va lues . 
The workable periods were calculated in 23 yea r s for five d ra in -
depths and three drainage in tens i t ies . 
RESULTS 
In figures 2 and 3 the effect of drainage intensity on total amount 
of workable days (cr i te r ion: u> < -300 cm) before May first a r e shown 
for drain depths 80 and 150 cm below surface . A drainage intensi ty 
-1 -1 
of 0, 01 day means that drainage discharge ra te is 1 cm. day if 
the groundwater table midway between two drain t i les is 100 cm 
above the d ra ins . A l inear relat ion between discharge ra te and hy-
draulic head was supposed to exis t . 
There seems to be but a smal l influence of drainage intensi ty on 
workabil i ty in spring. Fig . 3 shows considerable influence below an 
_1 intensity of 0, 003 day . But that has no prac t ica l meaning. Thus 
poorly drained soils a re not fit for a rable agr icul ture because of in-
undations in winter . The design intensi t ies used in the Nether land ' s 
drainage c r i t e r ion a re 0, 023 and 0, 007 day for r e s p . 80 and 150 cm 
drain depth. According to WESSELING (1969) thus drained soils have 
a groundwater depth of 25 cm occurr ing once per year . 
So in the appropr ia te range of intensi t ies the choice of the d ra in -
age intensity does hardly affect workabili ty in spr ing. 
The effect of drain depth is shown in fig. 4 and 5. These give 
the amount of days in which the top 5 cm was d r i e r than a mois ture 
tension of 300 cm. In many ye a r s the effect appears to be cons iderable . 
A single year (1970) showed no workable days before May. Other yea r s 
had few workable days combined with smal l effect of drain depth (1959, 
1962, 1966). Many yea r s were so dry ( e .g . 1968) that even very s h a l -
low drainage gave a lot of workable days . In such ye a r s inc rease of 
workabil i ty has not much sense . In about half of the ye a r s there is 
considerable influence of drain depth in a re levant range of workability. 
APPLICATION 
A probabili ty distr ibution of workable days in dependence of d ra in-
depth is shown in fig. 6. This is of course only valid for this loam soil 
and the wheather of the used 23 y e a r s in the Nether lands and for the 
workabi l i ty- l imi t of vp = - 300 cm. 
The higher the workabil i ty, the sma l l e r the requi red amounts of 
labour and equipment can be. F a r m e r s will choose these factors so 
that in only few y e a r s (e. g. 2 out of 10) the normal spring works can-
not be accomplished in due t ime . Fo r low probabil i t ies the workabili ty 
at 150 cm drain depth is about twice that of 80 cm depth. Increasing 
drain depth from 150 to 200 cm looks not very helpful. 
More probabil i ty dis tr ibut ions have been made from the model -
output for every 5-day period in March and Apr i l . This will be used 
in an optimization model by the Institute of F a r m Mechanics and 
Labour (IMAG). F r o m thus obtained knowledge it will be possible to 
calculate drainage benefits for minimizing farm cos t s . 
More workable days means also e a r l i e r workability in spring 
and that means ea r l i e r sowing and planting. P r i m a r i l y the e a r l i e r 
workabil i ty of deeply drained soils is caused by their lower mois tu re 
content than that of shallow drained soi l s . This causes a difference 
of some days in a dry period. This difference is amplified strongly 
by the i r r egu la r rainfall pat tern. 
Fig. 7 gives the workable periods ( y < - 300 cm) during March 
and Apri l for 4 drain depths in 23 y e a r s . The year I960 has been 
omit ted because the chosen initial condition at January f i rs t could 
influence the resu l t s considerably in that yea r . 
In every year the soil was the e a r l i e r workable the deeper it 
was drained. In some yea r s the difference was only smal l (1951), in 
other yea r s very big (1955). 
The re la t ion between sowing time and yield depress ion was in-
vest igated by WIND (I960). With the aid of this paper and the work-
able periods given by fig. 7 VAN WIJK and FEDDES (1975) calculated 
the yield depress ions , caused by lack of workabil i ty. They assumed 
that for sowing summer grains 5 days a r e requi red per farm and 
that sugarbeet and potatoes can be sowed ( r e sp . planted) together in 
5 days . Fu r the r they assumed that the f a rmer will use the f irs t 5 
available workable days. 
The yield depress ions thus calculated and averaged over 23 
yea r s a re given in table 1. 
Table 1. Yield depress ion caused by too late sowing, as a function 
of drain depth. The data a re averaged over the period 
1951-1973. After VAN WIJK and FEDDES 
Drain 
depth 
cm 
40 
80 
100 
150 
Summer 
grain 
% 
36 
18 
12 
8 
Potatoes and 
sugarbeet 
% 
12 
7 
6 
4 
The effect of drain depth is l a rge r for s u m m e r gra ins than for 
potatoes and sugarbeet . This can be explained by the ea r ly period in 
spring in which the former c rop is sown. During that t ime , F e b r u a r y 
and March , evaporation is low and the amount of mois ture in soil has 
big influence on the t ime which is r equ i red to obtain workabil i ty. 
Potatoes a r e planted, and sugarbee ts a r e sown not before March 20, 
because of frost hazard . In that period evaporation is higher and 
soil moi s tu re has l e s s influence. 
Table 1 gives the opportunity to calculate a benefit of dra inage . 
Assuming that in 4 yea r s 1 potato, 1 sugarbeet and 1 s u m m e r gra in-
_1 
c rop occur , and that the value of the yield is 2000 Hfl. ha for 
_1 
s u m m e r gra ins and 4000 Hfl. ha for the other c rops , the drainage 
-1 -1 
benefit is 250 Hfl. ha . year in the range between 40 and 80 cm 
depth. F o r the range 80-100 and 100-150 cm, the benefit is 50 and 
-1 -1 
60 Hfl. ha. . y e a r respec t ive ly . 
These data a re not sufficient, they have to be completed with 
the effect of drainage on farm cos t s , on workabili ty in autumn, on 
wate r damage to c rops and soil in winter . Moreover drain depth is 
a factor in drought damage which may occur in dry y e a r s . 
LITERATURE 
KEULEN, H. VAN and C. G. E . M . VAN BEEK, 1971. Water move-
ment in l ayered soils - A simulation model . Neth. J . A g r . S c i . 
19: 138-153 
WESSELING, J . , 1969. Bergingsfactor en d ra inagec r i t e r ium. 
ICW Mededeling 118 
WIND, G. P . , I960. Opbrengstderving door te laat zaaien. Landb. 
Ti jdschr . 72: 111-118 
, 1972. A hydraulic model for the simulation of non-
hes te re t i c ve r t i ca l unsa tura ted flow of mois tu re in so i l s . 
J. Hydr. XV: 227-246 
and W. VAN DOORNE, 1975. A numer ica l model for 
the simulation of unsa tura ted ver t i ca l flow of mois tu re in so i l s . 
J . Hydr. 24: 1-20 
WIND, G. P . , 1976. Application of analog and numer ica l models for 
an investigation of the influence of drainage on workabil i ty in 
spr ing. To be published in Neth. J . Agr. Sei. 
WIJK, A. L . M . VAN and R. A. FEDDES, 1975. Invloed van de water-
huishouding op de opbrengst van landbouwgewassen. 
ICW-nota 867 
number of workable days x 
14 o analog calculation 
x observation by Hokke 
1-15 April 
6 - 3 0 April 
19 5T 
Fig. 1. Observed and calculated numbers of workable days in 
23 years 
number of workable days 
25 r 
2 0 -
15 
10 
X 
0005 
66 
0,010 0,015 
drainage intensity A in days'* 
Fig. 2. Effect of drainage intensity on the total amount of workable 
days ( Y< - 300 cm) in March and April for drain depth 80 cm 
below surface 
number of workable days 
30 
drainage intensity A in days"1 
Fig. 3. As fig. 2 for drain depth 150 cm below surface 
workable days 
2 5 t -
. . - 4 6 6 
I 
Sö eb ioÔ" 1*8 Ï5Ö 200 
drainage depth (cm) 
70 
Fig . 4. Effect of drain depth on the total amount of workable days 
(<f < - 3 00 cm) in March and Apri l for the las t 8 y e a r s of 
calculation 
workable days March and Apr i l 
20 
. 5 8 
80 100 150 200 
drainage depth (em) 
Fig. 5. As fig. 4, for the years with poor workability of shallow 
drained soil 
workable days 
30p 
drain depth (cm ) 
200 
150 
Fig. 6. Probability distribution of total workability (y < - 300 cm) 
in March and April 
year 
workable if drain depth >40cm 
>100 
>150 
>2O0 
51 
52 
53 
54 
55 
56 
57 
5» 
59 
61 
62 
63 
64 
6 5 
66 
67 
68 
69 
70 
71 
72 
73 
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APRIL 30 
Fig . 7. Workable per iods for 4 drain depths («^ < - 300 cm) 


Workability and drainage

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