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IV. Influence of Rotations on Conservation and Productivity
SOIL MANAGEMENT FOR CONSERVATION AND PRODUCTIVITY
timothy sod, areas of Honeoye soil showed variations in corn yield from
49 to 69 bushels per acre, depending on the amount of erosion prior to
the sod treatment.
The above and other reports have shown that, in general, past erosion
reduces crop yields as compared with areas under similar cultural conditions where less erosion has occurred. From a comparatively long-time
viewpoint, effects of grass-legume rotations in maintaining or increasing
yields thus appear to be due in part to conservation effects of the rotation system.
Effects resulting from the rotation of cultivated truck crops with
grass-legume mixtures at regular intervals are reported by Neal and Brill
(1951). It is pointed out that the practice of growing cultivated crops
in rotation with grass-legume mixtures or other close-growing, noncultivated crops has long been followed in certain agricultural areas. It is
commonly recognized that such cropping practices aid in soil organic
matter maintenance and in weed and disease control, and improve soil
productivity. More recently it has become evident that such practices
improve physical conditions of the soil, thus providing better aeration
and drainage and reducing runoff and erosion losses. I n many areas,
however, the above factors have been only of incidental importance in
determining the cropping system to be followed. Economic need has
been the primary consideration. I n general farming areas and on dairy
and other specialized livestock farms there is commonly a need both for
the cultivated grain crops and for the forage crops produced in a good
rotation. I n such enterprises cultivated crops are commonly grown in
regular rotation with small grain and with grass-legume mixtures. The
rotation study reported here, however, was carried out on a New Jersey
Coastal Plain soil used for vegetable crop production. The soil type is
a Freehold loamy sand. I n this and similar vegetable-producing areas,
little or no livestock is kept on many of the farms. The replacement of
horses, as a source of farm power, by tractors and trucks has removed
all need for grass and legume crops as animal feed on these farms. I n
this situation the decision as to whether or not cultivated crops will be
grown, in rotation with sod crops rests on the effects of such a rotation
on soil and water conservation, on the physical condition of the soil, and
on soil productivity. I n the absence of immediate economic need for
the forage crops, many Coastal Plain areas have been cultivated continuously during recent years in the production of vegetable crops. Despite heavier fertilization, improved methods of disease and insect
control, and generally improved crop varieties and cultural practices,
the acre yields of a variety of vegetable crops have declined under this
system of soil management, as shown by Carncross (1948). It appears
that the influence of these several factors tending toward yield increases
has been nullified by the progressively reduced capacity of the soil for
production under the intensive and continuous cultivation practices followed.
In the rotation study conducted on this Coastal Plain soil, four rotations of the following characteristics were included :
Tomatoes, sweet corn, and peas followed by snap
Rotation I1 Tomatoes, sweet corn, and grass-legume sod.
Rotation 111 Tomatoes, followed by 10 tons per acre compost and
rye wintei cover, sweet corn followed by ryegrass and
vetch cover, and peas followed by ryegrass and vetch
Rotation I V Tomatoes followed by 10 tons per acre compost and
rye cover, sweet corn, and grass-legume sod.
The grass-legume seeding in Rotations I1 a n d I V was made without
a nurse crop in the fall following sweet corn harvest. The mixture included alfalfa; red, alsike, and crimson clover ; and timothy. One cutting of hay was removed, and all additional growth left to be plowed
The cultivated crops in all rotations were fertilized uniformly in
accordance with local recommendations. I n order to balance the total
fertilizer application in the different rotations, the sod mixture in Rotations I1 and IV received the same fertilization as the peas i n Rotations
I and 111.
Average soil and water losses from areas in each of the rotations are
shown in Table I.
Any of the rotations which included sod or regular winter cover
showed soil and water losses much lower than those from Rotation I.
Rotation IV, which included a year of sod, a compost application, and
cover each winter, brought about the greatest reduction in soil and water
The effectiveness of Rotation I11 in reducing soil and water losses
should be interpreted with some caution as compared with ordinary farm
practices for winter cover crops. I n this rotation the ryegrass-vetch
seeding following peas was made i n July. The mixture ordinarily made
a vigorous growth during the late summer and fall and occupied the land
for a period of about nine months. The ryegrass-vetch seeding following corn was made in late August and occupied the land for about seven
months. A compost application followed tomatoes, and a rye cover was
SOIL MANAGEMENT FOR CONSERVATION AND PRODUCTMTY
Average Soil and Water Losses under Four Rotations during a 6-Year Period
Average annual losses
Average growing seaaon $ losses
Average winter season losses
annual precipitation 45.81 inches.
Average growing season rainfall 28.93 inches.
t Values represent quantity of water lost as surface runoff.
$ Includes "-month period from April 1 through October 31.
on the land for about six months. Thus, Rotation 111, although it included a cultivated crop each year, was actually out of close-growing
vegetative cover for only about thirteen to fourteen months during each
three-year cycle. This cropping system cannot be directly likened to
one where long-season cultivated crops appear each year, with comparatively late seeding and early plowing of winter cover crops.
Evaluation of effects of the different rotations on soil properties which
influence runoff and erosion can best be made by comparing losses under
sweet corn and tomatoes. These crops appeared in each of the rotations.
Average soil and water losses during growing seasons are shown in
The soil and water losses shown in Table I1 occurred during growing
periods. Direct effect of sod and cover crops on runoff is not included
in these averages. All areas were plowed and cultivated in the same
manner during the period of measurement. It is evident that widely
different amounts of soil and water loss occurred from areas under the
different rotations. Losses from areas in Rotation IV, for example, were
considerably less than half those from areas in Rotation I during the
same periods of time. I n general, Rotations 11, 111, and I V were more
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Average Growing Season Losses of Soil and Water under Tomatoes and Sweet Corn
in Different Rotations
Water 1 0 ~ 8 ,
Least significant diff erence-Water loss
or less alike in conservation effectiveness, and all were much superior to
rotation I. The relative soil loss from the two crops under Rotation I1
is of interest. Tomatoes followed directly after the grass-legume sod
crop, and sweet corn was grown during the second year of cultivation
after sod. There was no winter cover between these crops. Soil loss
from tomatoes in Rotation I1 was lower than in Rotation 111, but the
order was reversed during the following sweet corn crop. It appears
that the compost treatment and cover crop preceding sweet corn in Rotation I11 had considerable effectiveness. This emphasizes a point mentioned above to the effect that frequency of application of organic matter
to the soil is an important factor in structure maintenance and conservation. It appears that the conservation effectiveness of Rotation I V
resulted from the fact that the substantial addition of organic matter to
be expected from the sod crop was supplemented by compost and a winter
cover during the following winter period.
I n this evaluation of the effects of the rotations on soil and water
losses, as shown in Table 11,no attempt is made to separate direct effects
due to improved soil physical conditions from indirect effects due to improved soil productivity. The latter is often an important factor in
conservation. Improvement of soil structure, induced by the rotations,
ordinarily stimulates crop growth, as will be shown later. The increased
density of vegetation, in turn, provides better protection for the soil
surface and thus reduces soil and water losses.
Yield data from this study show that the rotations and soil management systems most effective in reducing soil and water losses were also
most effective in increasing yields of cultivated crops. This general effect would be expected. It has been shown (Johnston et at,, 1942; Page
and Willard, 1946; Richards e t al., 1948) that rotations and cover crops
SOIL MANAGEMENT FOR CONSERVATION AND PRODUCTIVITY
improve physical conditions of the soil. Other reports (Peele and Beale,
1941 ; Wilson and Browning, 1945) have shown the relationship of certain physical soil conditions to both runoff and erosion and to crop yields.
It seems reasonable to expect that improved aggregation and porosity of
the soil would permit more rapid entrance of water a t the surface and
more rapid percolation to lower depths of the soil profile, thus reducing
runoff. These same conditions should provide better soil aeration and
hence more favorable conditions for plant growth.
Average annual yields of tomatoes and sweet corn from the four rotations included in the study are shown in Table 111.
Average Yields of Tomatoes and Sweet Corn under Four Crop Rotations, 1944-1949
no. 1 earslacre
Leaat significant difference-Tomatoea
Fertilizer applications were in accordance with local recommendations and were identical in each of these rotations throughout the period
of operation. Average yields during the period of two rotational cycles
varied inversely with soil losses in the different rotations. It appears,
as suggested above, that soil conditions which are favorable for conservation are also favorable for improved crop growth and yield.
Similar effects of rotation with grass-legume mixtures on both yields
and conservation are reported by Wilson and Browning (1945). This
report shows that after cropping for fifteen years to a corn, oats, meadow
rotation, corn yielded 94.4 bushels per acre in comparison with 24.4 bushels from a n adjoining plot in continuous corn for the same period, The
percentage of aggregates larger than 0.25 mm. for different crops was
in the order: continuous corn < rotation corn < rotation oats < rotation clover < continuous alfalfa < continuous bluegrass. The amounts
of soil loss and runoff were in an exact reverse order.
Page and Willard (1946) show that areas in a four-year rotation of
corn, oats, and two years of grass-legume sod had a degree of aggregation
of 54.2 per cent and yielded 67.9 bushels of corn per acre. Areas in continuous corn showed an aggregation value of 23.4 per cent and a corn
0. R. N
yield of 22.5 bushels per acre. The relationship of crop rotations and
soil management both to conservation of soil and water and to productivity is shown by Pierre (1945), who points out that most soil management practices aimed specifically at high crop yields also aid in the
control of soil erosion and in the conservation and efficient utilization of
rainfall. Wiancko et aJ. (1941) report that twenty years continuous
cropping to corn reduced yields by 33 per cent despite ample fertilizer
application. During the same period yields of corn following a grasslegume mixture increased from 56 bushels to 65 bushels per acre.
Browning ct aZ. (1948) report that corn after eleven years of alfalfa
yielded 106 bushels per acre, compared with 86 bushels on plots where a
three-yeax rotation had been followed for twelve years, and 76 bushels
an acre following eleven years of bluegrass. The yields of second- and
third-year corn following eleven years of alfalfa were 83.5 and 72.9 bushels per acre, respectively. Second- and third-year yields following the
bluegrass were 68.9 and 77.0 bushels per acre, respectively. Thus the
corn yields following alfalfa., although higher initially, showed a more
rapid decline than did those following bluegrass. Erosion losses from
first-year corn following either alfalfa or bluegrass amounted to only
0.1 ton per acre. During the following two years soil loss was 15.1 tons
from corn after alfalfa and 5.6 tons from corn following bluegrass.
Many reports indicate that grass is relatively more effective than
legumes in bringing about aggregation and a stable structural condition
in the soil. The preceding data seem to support this view.
Further data on the influence of soil management practices on physical condition and productivity of Coastal Plain areas have been reported
by the writer (1952). The soil areas involved in this study are devoted
largely to the production of vegetable crops. On any given farm the
acreage of a particular crop may vaxy widely from year to year, depending on anticipated market conditions and other factors. It is thus impractical to specify a fixed rotation listing the vegetable crops to be
grown. The term “land resting” was used in this situation to identify
a cropping system which included two or three years of cultivation followed by a year when the land was cropped to a grass-legume mixture
or other noncultivated, soil-improving crop or mixture. The land-resting practice thus limits the intensity of cultivation but does not specify
the sequence or even the particular crops to be grown during periods of
Sweet corn yields from a loamy sand soil in New Jersey following
different land-resting treatments are shown in Table IV.
As pointed out earlier (Neal and Brill, 1951), each of these landresting practices would be expected to reduce soil and water losses dur-
SOIL MANAGEMENT FOR CONSERVATION AND PRODUCTrVITY
TABLE, I V
Effect of Land-Resting Practices on Sweet Corn Production
Clover and timothy 1946
Ryegrass and vetch 1946
Winter cover and soybeans 1946
Winter cover and broadcast corn 1946
Yield-no. 1 ears/acre
1948 1949 Total for period
6,430 24,920 ( 4
8,580 27,870 ( 3
8,380 27,840 (3
7,850 31,140 (3
8,140 24,120 ( 3
ing subsequent years of cultivation. The data in Table IV show, in
addition, that sweet corn yields were increased markedly as a result of
the treatments. In three of the four cases, total production from three
crops following treatment- exceeded that from four crops on continuously
cultivated land with adequate fertilization.
The effect of these treatments on aggregation of silt and clay particles into aggregates larger than silt size is shown in Table V.
Percentage Aggregation of Silt and Clay Particles under Land-Resting Practices
Treatment in 1946
Clover and timothy
Ryegrass and vetch
Winter cover and soybeans
Winter cover and broadcast corn
(after 3 years
Results from the samples taken in late fall of 1946 show increased
aggregation of silt and clay particles under each of the land-resting
treatments. Analysis of the 1949 samples shows that this effect had
been largely or entirely lost in the course of three years of cultivation
with annual winter cover crops. These and other data and observations
have indicated that the improvements in structure and productivity of
the soil resulting from land resting are temporary. The effects are
largely lost during two to three years of clean cultivation. This temporary condition, however, can be permanently maintained by a systematic program of resting the land at intervals of every third or fourth
0. R. NEAL
I n addition to the above data from field plot tests, the land-resting
practice was tested on a number of privately owned farms in the vegetable-producing area of the New Jersey Coastal Plain. In general, the
procedure followed was to seed down an area of one-half acre or more
in a field that had been under clean cultivation for several years. The
remainder of the field was cultivated. Ordinarily no vegetative growth
was removed from the rested area during the year. In the following
year the rested area was brought into cultivation for comparison with
the remainder of the field. The crop or mixture used in the resting
treatment varied with the locality, with the type of cultivated crops produced on the farm, and with the grower's preference.
In a number of tests during 1950 certain physical properties of the
soil known to be related to conservation were measured a t the time of
yield measurement. Volume weight, percentage aggregation of silt and
clay particles, and amount of air-filled pore Upace in the plowed layer
were determined for the rested and nonrested areas. Data on dift'erences
in these properties and in yield under different treatments are shown
in Table VI.
Effects of the resting treatments on yields of cultivated crops and on
changes in physical properties of the soils were quite variable in extent.
This might be expected under the variable conditions between individual
tests. The direction of change due to treatment, however, was quite consistent. I n all the above cases, except one, the treatment reduced volume
weight of the soil and increased air-filled porosity, degree of aggregation,
and yield of subsequent cultivated crops. I n the one exception the reversal of each of these trends seems to indicate failure in selection of a
comparable field area for the test.
Improvement in the soil physical properties listed above has been
shown to be related to reductions in runoff and erosion. A practical and
effective method for maintaining favorable physical conditions in these
sandy soils is through some form of land resting, as defined above. The
grower following such a system will thus provide an important element
in a n effective conservation system and at the same time will increase
acre yields, and hence efficiency of production, of cultivated crops.
Recently a number of synthetic resin-like materials have been prepared, and offered on the market, for use in increasing and stabilizing
aggregation of soil particles. Such materials, if proved effective, would
provide the long-sought chemical means for maintenance of soil structural conditions a t a favorable level. It would then be possible for the
SOIL MANAGEMENT FOR CONSERVATION AND PRODUCTIVITY
Effects of Land-Resting Treatments on Crop Yield and Change in Certain Physical
Properties of the Soil
grown f o r
sorghum, 1949 - Tomatoes
Soybeans and Sudan
1948, 1949 -Field corn
Rye and vetch -Tomatoes
Crotalaria, 1948 -Field corn
lima beans, 1949 Sorghum, 1948 -Sweet
Cultivated i n
tomatoes, 1949 ~
Change in physical
land operator to purchase and apply a material for structure maintenance, thus avoiding the necessity for crop rotations which take a portion
of the land out of cultivated crops at regular intervals.
Martin e t al. (1952) report results from a study of one of the soilconditioning materials. Application of the material a t rates of 0.020.20 per cent of the plowed layer resulted in increased aggregation, parosity, and permeability of the treated layer. The aggregates were
water-stable, and the conditioning material was highly resistant to decomposition. The improved structural condition resulting from the
treatment continued through the second year of cultivation. Crop yield
responses to the treatment were variable, with substantial increases occurring in some cases.
A discussion of the probable nature of the aggregating action brought
about by these materials is presented by Swanson (1952). This report
also cites both favorable and unfavorable cases of crop response to the
0. R. NEBL
It is much too early to make an accurate evaluation of these materials
as agents for maintenance of soil structure. At the moment, there seems
no real possibility that compounds of this nature will replace organic
matter, since organic matter in the soil has other functions in addition
to improving structural conditions. It is quite possible that the soil
conditioners may serve to supplement the effects of organic matter in
providing a higher level and stability of aggregate formation. If further
study proves this to be the case, use of these materials may make possible
some change i n rotation practices toward an increase in percentage of
cultivated crops. Regardless of the effectiveness of these materials, the
cost a t the present time limits use to special conditions of high-value
crops. Widespread use in general agricultural areas will require a substantial reduction below the present cost level.
It is pointed out that plants require nutrients, water, and air for
growth. Knowledge of the amount and availability of nutrients does
not in itself provide indication of productivity. Air and water relationships are necessarily dependent on the amount and nature of pore space
in the soil. Porosity, in most soils, depends on the arrangement and
aggregation of soil pakticles. Aggregation, in turn, is influenced by
several factors, of which soil organic matter is one of the more important. Of the several factors influencing soil structure, organic matter
is one of the few subject to systematic management.
Reports are cited showing deterioration of soil structure as organic
matter supply is depleted. Cultivation operations, in addition to the
acceleration of organic matter decomposition, contribute directly to soil
compaction as a result of implement traffic. Under exposure of cultivation, soil aggregation at the surface tends to break down under raindrop
impact. As soil aggregates are dispersed under these influences, soil
particles become most closely packed, bulk density increases, and porosity volume is decreased. These changes in the physical nature of the
soil bring about reduced rates of water absorption, less favorable airwater relationships for plant growth, and increased amounts of runoff
Systematic rotation of cultivated crops with grass-legume mixtures
or other noncultivated, close-growing crops provides a practical and effective means for maintenance of favorable structural conditions in
cultivated soils. Data are cited showing effects of such soil management
practices on certain physical soil properties, on yields of cultivated crops,
and on the extent of runoff and erosion.
FOR CONSERVATION AND PRODUCTIVITY
A possible role of chemical soil conditioners in the maintenance of
soil structural properties is pointed out.
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