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IV. Influence of Rotations on Conservation and Productivity

IV. Influence of Rotations on Conservation and Productivity

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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 :

Rotation I

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




Average Soil and Water Losses under Four Rotations during a 6-Year Period

Rotation no.










Soil loss

Water loss


Average annual losses

Burface inches









Average growing seaaon $ losses










Average winter season losses













* Average

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

Table 11.

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


0. R. NEAL


Average Growing Season Losses of Soil and Water under Tomatoes and Sweet Corn

in Different Rotations


Rotation no.





Sweet Corn

Soil loss,


Water 1 0 ~ 8 ,


Soil 1088,


Water loss,


















Least significant diff erence-Water loss

Soil loss

0.48 in.

934 lb.

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



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

Rotation no.







Sweet corn,

no. 1 earslacre









Leaat significant difference-Tomatoea

Sweet corn



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-




Effect of Land-Resting Practices on Sweet Corn Production



Continuously cultivated

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

Aggregation (%)

Treatment in 1946

Continuously cultivated

Clover and timothy

Ryegrass and vetch

Winter cover and soybeans

Winter cover and broadcast corn



Fall 1946

Fall 1949

(after 3 years

of corn)











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




Effects of Land-Resting Treatments on Crop Yield and Change in Certain Physical

Properties of the Soil

R,esting treatment

and year

1950 crop

grown f o r


Soybeans and

sorghum, 1949 - Tomatoes

Soybeans and Sudan

grass, 1949


Soybeans, 1949


Soybeans, 1949


Lima beans

Vetch, 1949


1948, 1949 -Field corn


1948, 1949

Sweet corn

Rye and vetch -Tomatoes

Crotalaria, 1948 -Field corn

Cultivated in

lima beans, 1949 Sorghum, 1948 -Sweet

Cultivated i n


tomatoes, 1949 ~

Effect of



on yield,

per cent



per cent



per cent

































Change in physical

properties with



per cent


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

and erosion.

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.




A possible role of chemical soil conditioners in the maintenance of

soil structural properties is pointed out.


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Anderson, M. A., and Browning, G. M. 1949. Soil Sci. Xoc. Amer. Proc. 14, 370-374.

Bailey, R. Y., and Nixon, W. M. 1948. U. 8. Dept. Agr. Yearbook. pp. 195-199.

Baver, L. D. 1935. Rept. Am. Soil Survey Assoc. XVI, 55-56.

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Bradfield, Richard 1936. Rept. Am. Soil Survey Assoc. XVII, 31-32.

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Agr. Tech. Bull. 969.

Carncrose, John W. 1948. New Jersey Agr. Expt. Sta. Circ. 619.

Ekern, Paul C. 1950. Soil Sd. SOC.Amer. Proc. 16, 7-10.

Ellison, W. D. 1944. Agr. Eng. 26(4), 131.

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Elson, Jesse. 1943. Soil Sot. ,900. Amer. Proc. 8, 87-90.

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Kolodny, L., and Neal, 0. R. 1941. Soil Sci. SOC.Amer. Proc. 6, 91-95.

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Soc. Amer. Proc. 11, 43-46.

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1946. Soil Sci. SOC.Anwr. Proc. 11, 47-49.

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