16 textbox

Fig. 16.1

TILLAGE SYSTEMSTillage systems are often classified by the amount of surface residue left on the soil surface. Conservation tillage systems leave more than 30 percent of the soil surface covered with crop residue. This surface residue cover is considered to be a level at which erosion is significantly reduced (see figure 16.2). Of course, this surface residue cover partially depends on the amount and physical characteristics of residue left after harvest, which may vary greatly among crops and harvest method (for example, corn harvested for grain or silage). Although residue cover greatly influences erosion potential, the sole focus on it is somewhat misleading. Erosion potential also is affected by factors such as surface roughness and soil loosening. Another distinction is whether tillage systems are full-field systems or restricted tillage systems. The benefits and limitations of various tillage systems are compared in table 16.1

JILL– the number was incorrect in the following par. I have chaged it to 16.2—see next page for figure

Figure 16.2 Soil erosion dramatically decreaseswith increasing surface cover. (Fall plow (FP), fallchisel (FC), no-till (NT), corn = circles, soybeans= no circles). Modified from Manuring, 1979.

Fig. 16.3

Fig. 16.4

Fig. 16.5

Fig. 16.6

Organic No Till?Researchers at the Rodale Institute in Pennsylvania have developed innovative cover crop management equipment that facilitates growing row crops in a no-till system. An annual or winter annual cover crop is rolled down with a specially designed front-mounted heavy roller-crimper, resulting in a weed-suppressing mat through which it is possible to plant or drill seeds (figure16.7) or set transplants. For this system to work best there must be sufficient time allowed for the cover crop to grow large before rolling/crimping so that the mulch can do a good job of suppressing weeds. Cover crops must have gone through the early stages of reproduction in order for the roller/ crimper to kill them, but not be fully matured to avoid viable seeds that could become weeds to the following crop. Since timing of any farm operation is critical, careful attention to the details of these biologically based systems is for them to be successful.

Figure 16.7 (see next slide) is in a text box that reads as follows:

Figure 16.7 Roller/crimper creates a weed-suppressing cover crop mat through which it is possible to plant seeds or transplants. Here cotton is being planted behind rye that has been traveled over by the roller/crimper. (photo by Jeff Mitchell)

Table 16.2Soil Health Indicator Plow-Tillage No-Tillage

Physical

Aggregate stability (%) 22 50

*Bulk density (g/cm3) 1.39 1.32

*Penetration resistance (psi) 140 156

Permeability (mm/hr) 2.1 2.4

Plant available water capacity (%) 29.1 35.7

Infiltration capacity (mm/hr) 1.58 1.63

Chemical

Early season nitrate-N (lbs/ac) 13 20

Phosphorus (lbs/ac) 20 21

Potassium (lbs/ac) 88 95

Magnesium (lbs/ac) 310 414

Calcium (lbs/ac) 7172 7152

*pH 8.0 7.8

Biological

Organic matter (%) 4.0 5.4

Cellulose decomposition rate (%/week) 3.0 8.9

Potentially mineralizable nitrogen (g/g/week) 1.5 1.7

Easily extractable glomalin (mg/g soil) 1.2 1.7

Total glomalin (mg/g soil) 4.3 6.6

Fig. 16.8

Fig. 16.10