Description Usage Format Details Source References Examples

Yield of corn, alfalfa, clover with two fertilizers

1 | ```
data("heady.fertilizer")
``` |

A data frame with 81 observations on the following 3 variables.

`crop`

crop

`rep`

replicate (not block)

`P`

phosphorous, pounds/acre

`K`

potassium, pounds/acre

`N`

nitrogen, pounds/acre

`yield`

yield

Heady et al. fit two-variable semi-polynomial response surfaces for each crop.

Clover and alfalfa yields are in tons/acre. The clover and alfalfa experiments were grown in 1952.

Corn yields are given as bu/acre. The corn experiments were grown in 1952 and 1953. The same test plots were used in 1953 and in 1952, but no fertilizer was applied in 1953–any response in yield is due to residual fertilizer from 1952.

All experiments used an incomplete factorial design. Not all treatment combinations were present.

Earl O. Heady, John T. Pesek, William G. Brown. (1955). Crop Response Surfaces and Economic Optima in Fertilizer Use. Agricultural Experiment Station, Iowa State College. Research bulletin 424. Pages 330-332. https://lib.dr.iastate.edu/cgi/viewcontent.cgi?filename=12&article=1032&context=ag_researchbulletins&type=additional

Pesek, John and Heady, Earl O. 1956.
A two nutrient-response function with determination of economic optima
for the rate and grade of fertilizer for alfalfa.
*Soil Science Society of America Journal*, 20, 240-246.
https://doi.org/10.2136/sssaj1956.03615995002000020025x

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | ```
library(agridat)
data(heady.fertilizer)
dat <- heady.fertilizer
libs(lattice)
xyplot(yield ~ P|crop, data=dat, scales=list(relation="free"),
groups=factor(paste(dat$N,dat$K)), auto.key=list(columns=5),
main="heady.fertilizer", xlab="Phosphorous")
# Corn. Matches Heady, p. 292
d1 <- subset(dat, crop=="corn")
m1 <- lm(yield ~ N + P + sqrt(N) + sqrt(P) + sqrt(N*P), data=d1)
summary(m1)
# Alfalfa. Matches Heady, p. 292. Also Pesek equation 3, p. 241
d2 <- subset(dat, crop=="alfalfa")
m2 <- lm(yield ~ K + P + sqrt(K) + sqrt(P) + sqrt(K*P), data=d2)
summary(m2)
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 1.8735521 0.1222501 15.326 < 2e-16 ***
## K -0.0013943 0.0007371 -1.891 0.061237 .
## P -0.0050195 0.0007371 -6.810 5.74e-10 ***
## sqrt(K) 0.0617458 0.0160142 3.856 0.000196 ***
## sqrt(P) 0.1735383 0.0160142 10.837 < 2e-16 ***
## sqrt(K * P) -0.0014402 0.0007109 -2.026 0.045237 *
# Clover. Matches Heady, p. 292.
d3 <- subset(dat, crop=="clover")
m3 <- lm(yield ~ P + sqrt(K) + sqrt(P) + sqrt(K*P), data=d3)
summary(m3)
# Corn with residual fertilizer. Matches Heady eq 56, p. 322.
d4 <- subset(dat, crop=="corn2")
m4 <- lm(yield ~ N + P + sqrt(N) + sqrt(P) + sqrt(N*P), data=d4)
summary(m4)
## Not run:
libs(rgl)
with(d1, plot3d(N,P,yield))
with(d2, plot3d(K,P,yield))
with(d3, plot3d(K,P,yield))
with(d4, plot3d(N,P,yield)) # Mostly linear in both N and P
rgl.close()
## End(Not run)
``` |

Embedding an R snippet on your website

Add the following code to your website.

For more information on customizing the embed code, read Embedding Snippets.