Module 7.2: Conservation Agriculture: A Systems Approach
Module 7.2: Conservation Agriculture: A Systems Approach jls164Tillage can incorporate soil amendments such as fertilizers; bury weed seeds and crop residues that may harbor diseases and insects; remove residue that insulates the soil and promotes soil warming and crop seed germination and growth. Tillage can also cause soil erosion, disrupt soil organisms and soil structure; and remove residues that slow water run-off and evaporation, conserving soil moisture. Conservation tillage practices can reduce or eliminate the need for tillage, and the integration of perennials and cover crops can also protect soil from erosion and contribute to improving soil quality. In Module 7.2, we explore tillage and cropping practices that farmers can employ and integrate to conserve and improve their soil for long-term farm productivity.
Tillage Impacts on Soil Health
Tillage Impacts on Soil Health hdk3In addition to exposing soil to wind and water erosion, tillage can alter the physical structure, distribution of organic matter, and biological activity of soil. At the depth where the plow impacts the soil, a layer of soil compaction can develop (a plow pan), limiting water infiltration and plant rooting depth. Under tillage, crop residues, roots and root hairs, and their associated fungal hyphae are disturbed and more decomposed in the plow layer. By contrast, when roots, fine roots, and fungal hyphae are not disturbed and decomposed as rapidly, there are more channels that water, air, earthworms, and roots can move through, and soil aggregation is enhanced. Below is a schematic comparing the root zone profile of a conventionally tilled soil to a no-till soil.

Watch the three videos below, from USDA NRCS about soil tillage and soil health.
Video 1: The Science of Soil Health: What Happens When You Till? USDA NRCS (3:05)
Video 2: The Science of Soil Health: Nightcrawlers and Soil Water Flow. USDA NRCS (3:05)
Video 3: The Science of Soil Health: Compaction USDA NRCS (4:26)
Tillage Systems
Tillage Systems hdk3Humans have developed many different ways to prepare the soil to plant crops, with the primary goal of achieving good seed to soil contact to keep seeds moist as they germinate and grow. There are some benefits of tillage. For instance, tillage enables the farmer to bury or mix-in crop residues that insulate the soil and keep it moist and cool which can delay crop seed germination in cool environments. By burying the insulating crop residues, solar radiation can warm the soil more quickly. Tillage can also terminate weeds, cover crops or perennials, and bury weed seeds and crop residues that may harbor pathogens and insect seeds; tillage also mixes in soil amendments, such as fertilizer and animal manures.
In conventional tillage systems, primary tillage equipment such as the moldboard plow or a rototiller inverts the soil. A second tillage event or plow is often used afterward to break up large soil clods into smaller particles, with the goal of improving seed to soil contact. See photos below.



Removing or mixing-in crop residue leaves the soil exposed and prone to wind and water erosion, as well as soil moisture loss. Tilling crop residue into the soil also makes residues more accessible to soil organisms and incorporates oxygen into the soil, increasing the decomposition rate of the residues and decreasing organic matter content at the soil surface and plow layers. Tillage also disrupts soil organisms, particularly mycorrhizal fungi, and soil physical properties such as water stable aggregates.
Conservation tillage or minimum tillage is another soil preparation method designed to reduce soil erosion by reducing disturbance and leaving some plant residue (at least 30%) on the surface. The soil is not inverted, but the surface is disturbed and often a high proportion of crop residues are mixed in with tillage equipment such as a disk plow or a chisel plow.
No-till or Direct-seeding is designed to eliminate tillage, by cutting a slit in the surface and placing the seed in the slit. In addition to minimizing crop residue disturbance, the crop is planted in one pass across the field, thereby reducing erosion, labor, and fuel needed to prepare a field and plant the crop.


Some hurdles to no-till adoption As discussed earlier, there are a number of reasons that farmers till the soil. For instance, conventional tillage can terminate perennials, cover crops, and weeds prior to planting the subsequent crop. Without conventional tillage, farmers typically use herbicides to terminate the previous perennial or cover crop and control weeds. In cool environments, crop residues can harbor pathogen and insect pests, and insulate soil, which can slow soil warming in spring and delay crop emergence. These factors can reduce crop yield, particularly if farmers don't rotate crops to interrupt pest life cycles. In addition, although farmers typically need less tillage equipment to plant with no-till, there is an initial cost associated with purchasing no-till equipment for farmers who use conventional or conservation tillage equipment. And with new equipment, farmers need to learn how to adjust no-till planters to ensure that seed is planted at the optimal depth. Consequently, no-till planters are typically heavier to cut through crop residues and place seeds at a sufficient depth for good seed to soil contact.
Zone or strip tillage When soils have high crop residue and/or are high in organic matter, or are not well-drained, soils can remain cool and delay seed germination. Zone tillage or strip tillage incorporates the insulating crop residue in a narrow zone or strip of soil where the seed is placed. Residue between the seed planting zones is not disturbed or removed. Removing the soil insulating layer increases the rate of soil drying and warming in close proximity to the seed, promoting earlier seed germination compared to soil with residue left intact.

Reading
Read more about tillage and how it impacts soil, in Chapter 16 (Reducing Tillage) of Building Soils for Better Crops.
Continuous Cover Through Crop Management
Continuous Cover Through Crop Management hdk3Soil conservation practices are most effective when they reduce soil disturbance or tillage and also maintain live plants in the soil.
As discussed in Module 5, perennials provide year-round live plant cover that protects soil from erosion; and their live and large root systems support rhizosphere activity and return organic matter to the soil all year. To provide continuous live roots for soil conservation and soil health, perennial crops can be rotated with annual crops, and double crops and cover crops can be integrated into annual cropping systems. Recall that in Module 7.1, a dairy crop rotation of corn-alfalfa was shown in Fig. 7.1.3b, and double cropping in Fig.7.1.4. The photos below also illustrate examples of how year-round cropping provides multiple agroecosystem benefits.
In addition, consider how managing crops and soils for soil conservation and health can enhance agricultural resilience and adaption to climate change. For instance, by increasing soil organic matter content, agricultural soil can: i. contribute to carbon sequestration (removing carbon dioxide from the atmosphere and storing it in soil), ii. improve soil structure and porosity and enhance water infiltration and water content in soil, and iii. store and cycle nutrients. Perennial crop production and double-cropping can utilize potentially longer growing seasons; provide more year-round protection of soil from erosion, and planting and harvesting crops at multiple times of the year can reduce the risk of extreme weather events or irregular weather interfering with cropping activities.



For more discussion of a crop-soil system management approach, watch the three short videos below from NRCS about the benefits of cover crops on soil health.
Video 1: The Science of Soil Health: Using Cover Crops to Soak up Nutrients for the Next Crop USDA NRCS (3:08)
Video 2: The Science of Soil Health: Without Carrot or Stick USDA NRCS (2:39)
Video 3: The Science of Soil Health: Cover Crops and Moisture USDA NRCS (3:26)
Check Your Understanding
Describe two or three practices that are components of the conservation system or agroecological approach of soil conservation and health.
Reduced soil disturbance through reduced tillage, particularly no-till or zone/strip tillage; Continuous plant cover through the integration of perennials, double crops, and cover crops. Returning organic matter to the soil through the application of animal manure, compost, and the integration of green manure and cover crops that are returned to the soil.
Conservation Agriculture in Brazil Case Study
Conservation Agriculture in Brazil Case Study jls164Activate Your Learning
Go to the FAO UN website and read their brief description of Conservation Agriculture. Then watch the short video “Conservation Agriculture in Southern Brazil” (4:41).
Conservation Agriculture in Southern Brazil
PRESENTER: In Santa Catarina and Piranha, southern Brazil, severe soil degradation over the past two decades left many farmers with no choice-- find a solution or abandon the land. Roland Ristow began experimenting with no-tillage farming more than 20 years ago. He is considered a pioneer of conservation agriculture.
ROLAND RISTOW: [NON-ENGLISH SPEECH]
INTERPRETER: Before starting conservation agriculture, there was a lot of work to do-- plowing harrowing, tilling. And then erosion would carry off all the water. If we hadn't changed over, all these would be desert now, and there would be no crops, just stones.
PRESENTER: Cover crops are the key. Grown between annual crops, they protect the soil from the damaging effects of heavy rainfall, sun, and wind, provide nutrients, and facilitate water infiltration by reducing soil compaction. By integrating livestock production, Francisco Sedosvki saves money on feed and effectively lets the cows prepare the land for direct seeding of his next crop.
His integrated approach to resource management, which includes pig raising and fish farming, actually improves the quality of the local water supply. This farm is a model of environmentally-friendly recycling.
FRANCISCO SEDOSVKI: [NON-ENGLISH SPEECH]
INTERPRETER: We don't have to worry now because we have clean water on our farm. There's no animal waste in our stream. The situation has really improved. We can raise pigs without damaging the environment.
PRESENTER: Direct seeding makes conservation agriculture considerably less labor-intensive than conventional farming and more cost-effective. The elimination of tillage reduces machinery and fuel costs, while cover crops reduce the need for expensive chemical inputs. And even in dry years, yields increase as soil quality and water infiltration improves.
DERLI BOITA: [NON-ENGLISH SPEECH]
INTERPRETER: With conservation agriculture, you save money and you can produce more. I don't know the exact figures, but I think that our production has increased by about 30% or 40%.
PRESENTER: Time saved with conservation agriculture is used by farmers to diversify production and supplement their income. Products like sugar and jam can be sold all year round to ensure financial security for small-scale farmers. In southern Brazil, conservation agriculture has made sustainability a reality, and the Food and Agriculture Organization is already promoting the same approach in Africa and Central Asia.
JOSE BENITES: [NON-ENGLISH SPEECH]
INTERPRETER: I think that conservation agriculture really could solve a food security problem, and it could also be a valuable weapon in the fight against poverty.
PRESENTER: For many families in southern Brazil, that fight has already been won by making the most of natural resources and letting nature take its course.
After Watching the Video, Answer the Following Three Questions:
Question 1 - Short answer
Describe the soil and crop management practices that the video about Conservation Agriculture describes that promote soil quality and crop productivity.
i. No-till farming, ii. Cover crops that protect the soil from erosion, provide nutrients, and reduce soil compaction, iii. Integrating livestock and crop production.
Question 2 - Short answer
In Brazil, what were some of the ecological benefits of conservation agriculture?
i. Soil is protected and conserved, ii. Soil quality has improved, iii. Cover crop roots reduce soil compaction and improve water infiltration into the soil, iii. Integrating livestock and crop production helps recycle nutrients, and with fish-farming, there is less animal waste in the stream.
Question 3 - Short answer
In Brazil, what were some of the socio-economic benefits of conservation agriculture?
i. No-till or direct-seeding saves labor and time to plant crops, reduces machinery needs and saves money, ii. With reduced tillage and cover crops, farmers need fewer inputs, have saved money, and production has increased, iii. Time saved has allowed farmers to diversify production and produce added-value products.