**2. Primary tillage**

The primary tillage aims at maintaining or improving the soil structure and soil fertility. In addition, the strategy and operational execution of tillage greatly affect the weed. The soil structures enable the drainage and water absorption. The porosity for drainage and the water capacity of the upper soil layer is controlled by the microbes and the content of organic matter. This is maintained by the incorporation of fresh organic matter with smooth tillage operations. At the same time, at stable conditions, the planning and performance of the primary tillage must ensure that no increase in the occurrence of the root-emerging weeds occurs. To control root-emerging weeds, the plant must be covered in the soil layer the deeper the better. Normally a depth of approx. 20 cm is recommended. This conflicts with the preferred conditions for the turnover of plant residuals and is supported by the presence of a smooth mix into the soil having access to the oxygen from the air and soil moisture getting into contact with the soil fungal and fauna that catalyze the process. Jacobs et al. [8] test has shown that the best conditions for the turnover of plant residuals are placements in the upper soil layer—0–5 cm. In practical the working depth of approx. 20 cm for the primary tillage is used. The experience is that this gives a good balanced result, just that the operator must be aware, that the working depth must be as shallow as possible. Deeper working depth increases the effect due to weed control but reduces the access to oxygen. Tillage operations may not be overdone in intensity as the operations are highly energy consuming. Also, that the tillage is not only positive. Unnecessary tillage damages the soil structure, this both due to the workability in the seed bed preparation, and the porosity. The challenge for the tillage operations is to support the dynamics of the growing system, not the operation itself.

If it occurs from the monitoring of the fields, that it is necessary to apply a dedicated treatment to reduce the occurrence of root emerging weeds this can be done in more ways. One obvious method is to increase the working depth for the primary tillage operation, and to make sure, that all the residuals are effectively covered deeply under the soil layer. Another more dedicated method is to make space in the crop rotation; this allows for a series of operations in the period after harvest. Here there are in principal two different methods: "drying" and "starving". Convenient conditions allow additionally to cultivate just prior to a period with temperatures below 0°C.

#### **2.1. The type of operation**

spring and autumn. It is important to have in mind that fast-germinating and established crops are highly competitive and contribute substantially to weed control [3]. Another specific element is the benefit of cutting perennial forage grass in the rotation three times or more per year to control quack grass and other root-emerging weeds. With respect to the direct control methods, it is important that the crop rotation allows for space to perform dedicated quack grass control after harvest. The presence of row crops allows one to perform the control by hoeing during the growing season. This potentially gives a good weed control but can also

The tillage operations are, in general, divided to be part of the primary tillage or the preparation of the seedbed. The primary tillage is aimed to obtain a good turnover of the plant residuals and to maintain a healthy soil structure. In this multi-oriented context, the demands for the tillage operations can be different if it is related to optimizing the soil fertility or the weed control. An example here is the performance of the moldboard plowing. Aiming for an effective control of perennial weeds demands that the plants are cowered deep in the soil or that they are dried out in a starvation strategy. Whereas the requirements related to the soil fertility can with good conditions be fulfilled by more superficial treatments. In fact, an unnecessary intensive tillage strategy will cause harm to the soil fertility [4, 5]. Therefore, in the operative planning, it is very important to be aware of the actual field conditions for the

The performance of the operations for seedbed preparation and seeding also affect the weed germination and the weed control. The goal of this operation is to do the final leveling of the soil surface and to establish the right structure for the soil aggregates to form the best possible conditions for the seeds to germinate and establish growth. If the time schedule allows, it can be beneficial to perform a weed harrowing prior to the seeding to reduce the density of the first generation of germinating weeds. In the seeding operation, it is off course important to establish the best possible conditions for the seed. A quick and fast germination and establishment of the crop is important to optimize the competitiveness against the weed. In addition, a uniform seeding depth is important for the subsequent weed control, in a way that this enables room for weed harrowing prior to the crop seeds that break through the soil surface [6, 7]. A uniform seeding depth causes a uniform germination and propagation of the crop plants, and thereby the best possible conditions for the following weed control by weed harrowing or hoeing.

All this together makes good sense to involve the principles of precision agriculture, also to support the effectiveness of the contribution to the weed control. This can be site-specific primary tillage, site-specific seedbed preparation, fixed tracking and controlled traffic, imple-

The primary tillage aims at maintaining or improving the soil structure and soil fertility. In addition, the strategy and operational execution of tillage greatly affect the weed. The soil structures enable the drainage and water absorption. The porosity for drainage and the water

cause substantial problems if the operation fails.

18 Biological Approaches for Controlling Weeds

specific year, and thereby also the infield variations.

ment control in general, and row control of the hoeing process.

**2. Primary tillage**

In Scandinavian countries, as in many other countries, the primary implements used for the primary tillage has been the moldboard plow and the stubble cultivator. Often, the stubble cultivator is used for a shallow operation immediately after harvest to stop the growth and cut the roots of weed plants and to catalyze the contact from the microbiological life to the residues. Hereafter, the strategy is different and highly dependent on the crop rotation and local conditions. If there is a need for a dedicated treatment to reduce the occurrence of perennial weeds, it is generally after harvest that a series of repeated stubble cultivations can be performed [4]. Danish tests show that repeated stubble cultivations in the autumn can reduce the density of perennial weeds up to 90%. Similar results can be seen in a test in Norway and Germany [9, 10]. Under wet conditions in Norway, it has been observed that the best results are obtained by applying the treatment in spring prior to moldboard plowing and seeding. By this method, the time for seeding becomes too late and too costly in yield reduction. In the autumn, as the temperatures are getting lower, the plowing operation is performed. Here, the growth is stopped, and the turnover of the residuals are continued, now integrated into the soil and sowed in some depth.

In areas having problems with erosion and where the farmers want to perform a strategy that is highly focused on soil fertility, deeper cultivation with chisel plows are used instead of the moldboard plowing. Under nonchemical conditions, success rate for this strategy to work is hard to come by. One major challenge is keeping a check on the development of the weed species in a way that it damages the yield and growth conditions for the crops. Although more tests have shown that the most important factor in weed control is the soil fertility and the composition of the crop rotation [11–13], It is shown that when the crops are healthy and the yield is high, it can be acceptable that there is some presence of weed the tests also shows that it is possible to control the weed not to develop uncontrolled. Although the earlier mentioned tests have shown that tillage, especially stubble cultivation or hoeing can be helpful in practical use to control the weed.

if plant residuals primarily are mixed in the lower layer of the plowing profile or if they are

The Effect of Tillage on the Weed Control: An Adaptive Approach

http://dx.doi.org/10.5772/intechopen.76704

21

The dedicated strategy in relation to optimizing the soil structure by using existing technology relies more on the operation only for the areas, where the operation is needed. In these situations, it is important to be aware, that the tillage operation is only a part of the solution. The aim here is in a gentle way to loosen the soil as a part of a plan involving more actions that together are aiming to revitalize the soil fertility, that beneficially also involves the introduction of dedicated crops, where the roots actively contribute to soil loosening and applying

The state-of-art research in drone technology is concerned not only with mapping the density of weeds but also determining the species [15, 16]. This information will be beneficial as the growing weed species can be used as indicators for soil fertility, and hereby there are also problems with drainage and water capacity. This is important due to crop growth and yield, but it also plays a very important role in weed management as the fertile soil generates vital

Due to this context, it makes sense to pay most attention to the optimization of soil fertility by

Ideally, the seed bed preparation must take place some days prior to seeding. This performs the task smoothly in the soil. During the days of rest prior to seeding the soil aggregates stabilize, such that the soil structure after seeding has less risk to slam and potential for erosion. Due to weed control the seed bed preparation prior to the seeding operation has another advantage as it can be used as a false seed bed, initiating weed seeds to germinate, and then removed in the seeding operation. In the planning of crop rotation, it makes good sense to make space for the false seed bed operation prior to the seeding of selected spring crops. More tests have been performed to reduce the pool of weed seeds in the soil. Results show that this is almost impossible [17, 18]. The seeding operation is normally performed by the use of implements, that also involves some tillage in the top layer. For a good establishment of the crop, precise seeding depth is important. This is also an advantage for weed control, as it is possible then to perform a weed harrowing operation just prior to the time where the new seeds breakthrough the soil surface. Hereafter it is important that crops perform a fast and robust establishment in this that the crops benefit from fertile soil, due to access to fertilizers, moisture, and the soil structure. Problems with slammed soil surface restrict the access for oxygen into the soil and thereby inhibit the growth. For more cases, the first establishment of the crop is essential. Due to weed control, it is in this period that the competitive strength of the crop due to weeds is established. In the next section, it is described how the competitive strength for crops improves the possibility of getting good results with weed harrowing. More tests [19, 20] show the importance of the timing in the tillage and weed management operations. Due to competitive characteristics there can be two alternative systems

placed into the bottom of the profile to optimize the control of root-emerging weeds.

organic matter from manure, compost, or similar.

means of the tillage system and other means.

**3. Seed bed preparation and seeding**

and robust grooving crops, that compete effectively with the weed.

#### **2.2. Data and precision agriculture in primary tillage**

The system of precision agriculture has been developed during the last three decades. The focus has primarily been on fertilizing and pesticide applications. There has been limited focus on the tillage no matter that there are big potentials both due to savings in cost and energy and in the optimization of the operations. The problem is that the controlling parameters such as "soil fertility" are almost impossible to measure by commercially available sensors or sensor systems. In addition, it is quite difficult to transform to a mathematical model.

Though there are potentially gains both in a planning and graduated intensity over the field that can be performed by use of existing technology. For example, the plowing depth can be controlled by both semi-automated means and automatically [14]. From an overall point of view, the precision-based application can be performed at least due to tree challenges that normally occur locally and delimited on the field:


The abovementioned effects can be mapped by manual inspection. In recent years, the use of drones for these types of inspections is developed for commercial use [15, 16]. Since the last approx. 2 decades, the global positioning system (GPS) positioning, the tractor computers, and auto guidance have been commercially developed and are now installed on more than 50% of new tractors. Having the digital application map, it is therefore possible to perform precision-controlled tillage operations. This can be done using selected implements that allow for the wanted adjustments, where the precision-based operations in farm level are introduced in the strategy of utilizing possible benefits and build the necessary profile of knowledge and technology needed to be prepared to utilize the upcoming versions of the new implement prepared for precision applications. One example here is the plow. Here, it is already possible to adjust the plowing depth within a given range using existing technology. New developments [14] show systems that are dedicated for depth control in the individual plowing sections. It is also possible to build on double plow sections in front of the main moldboard that controls if plant residuals primarily are mixed in the lower layer of the plowing profile or if they are placed into the bottom of the profile to optimize the control of root-emerging weeds.

The dedicated strategy in relation to optimizing the soil structure by using existing technology relies more on the operation only for the areas, where the operation is needed. In these situations, it is important to be aware, that the tillage operation is only a part of the solution. The aim here is in a gentle way to loosen the soil as a part of a plan involving more actions that together are aiming to revitalize the soil fertility, that beneficially also involves the introduction of dedicated crops, where the roots actively contribute to soil loosening and applying organic matter from manure, compost, or similar.

The state-of-art research in drone technology is concerned not only with mapping the density of weeds but also determining the species [15, 16]. This information will be beneficial as the growing weed species can be used as indicators for soil fertility, and hereby there are also problems with drainage and water capacity. This is important due to crop growth and yield, but it also plays a very important role in weed management as the fertile soil generates vital and robust grooving crops, that compete effectively with the weed.

Due to this context, it makes sense to pay most attention to the optimization of soil fertility by means of the tillage system and other means.
