**3. Seed bed preparation and seeding**

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 practi-

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

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

cal use to control the weed.

20 Biological Approaches for Controlling Weeds

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

normally occur locally and delimited on the field:

**1.** Emerging problems with root-emerging weeds

**2.** Dense soil with low capacity of water accessible for the crop

**3.** Compacted soil with reduced efficiency in the drainage

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 for seeding: one is that the seed is distributed evenly over the area to give the best coverage possible and thereby the best competitive strength against weeds. Danish experiences show good results with this system for crops such as rye and barley. If the crop is less competitive in general, or particularly in the early stage, another system can be favorable, to grow crops in rows this enable the possibility of performing weed harrowing and hoeing. In row cropping, the competitive strength due to weeds in the in-row area has improved substantially, as also the overall resistance for the crop in operations as weed harrowing is improved. The disadvantage of row cropping is that operations for weed control are needed in the inter-row area. Due to yield the crop is not that sensitive. The Danish test has shown that for row distances, up to approx. 18 cm for cereals, there is almost no decrease in yield. Other crops such as rape are even less sensitive to the open row distance.

distributed by an active control system. The intensity from the tines to the soil surface is controlled by the load on the section and the working angle for the tines. This working angle can also be controlled by a central control system that is normally controlled by the operator. The challenge for the operator is to adjust the settings for the harrow and the operation forward speed such that the damage on the crop is limited and the effect on the weeds is optimized. One important factor here is to make the best use of all factors to optimize the growth difference, such that the crop continuously is bigger and more established than the weed. It is also important that the soil is workable without a slammed and hard surface. In an optimal setup the first treatment is performed approx. 1 week before the seeding process to initiate the germination of the first generation of weed seeds. Hereafter follows a precision seeding as earlier described; this does reset the weeds. Then, just before the crop breaks the soil surface, a weed harrowing operation is again performed. Hereafter a break is needed for the crop to be established such that it sustains a next operation. For this operation the operator needs to pay the most attention to the timing and to the adjustment of the harrow as the best result is achieved by carrying out the operation as early as possible, without damaging the crop and when it is still possible to control the weed. Hereafter two more operations can be performed. As described the weed harrow is a uniform implement that work in the full working with based on the preconditions that it is possible to establish a difference in the sensitivity for the crop and the weed to the treatment. In comparison to this is the hoe that only operates in the inter-row area without crops. By modern implements the guidance of the hoe can be automatically controlled by a vision-based system that enables the hoe to operate quite precisely in relation to the row. As the competitiveness from the row of crops is bigger and closer to the row, it is important to perform hoeing as close as possible without absolutely damaging the crops. A very precise and dedicated operation can be performed by a hoe equipped with elements such as brushes or other tools that work close to the row. The advantage of the hoe

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23

A normal cropping system does normally include weed harrowing for weed control. The overall effect and weed control can be improved by also introducing the hoe for operations where it can be possible operated. Compared to weed harrowing the hoe is less sensitive on hard surfaces and so on, which means that the effect of hoeing is more reliable. Hoeing can also be an important part of the strategy to bring the system back to normal for areas where the weed has had the chance to develop to a level that is problematic for balance in the system. This can be done by opening the rows to make space for the hoe operations in the problematic areas in the field. The hoe is very efficient in the inter-row area. For the operation close to the row some additional systems can be built [21] such as flexible tines or rotating fingers.

Many farmers and research activities have shown that it is possible to control the weed in cropping systems only by use of mechanical and agronomic means. It is essential that the cropping system is carefully planned and adaptively optimized in relation to the local conditions and challenges. The fertile soil is key both to the growth and to the yield of the crops but

is that it has very high efficiency in the inter-row area.

**4. Discussion and conclusion**

#### **3.1. Digital tools**

Due to seeding there are commercial systems that allow for graduated seed density over the field. The graduation can aim for eliminating locally weak conditions for germination or if an improved coverage is required in the early stage. The control input for this must be given by the operator prior to the operation, as there are no systems available that can sense the input for this. Modern seeding implements are designed to operate with a constant seeding depth, with mechanical means that is adjusted prior to the operation in the field. Ongoing research aims to develop systems that by monitoring the actual working depth are adjusted by a dedicated control system. In the system tested the control systems are operating individually on each seeding section. With such a system in operation I will make sense to expect a coming version designed for adaptive control of the seeding depth, for example, to ensure the access to moister and thereby the best possible conditions for germination.

Systems for automatic change from broad seeding to row cropping are also commercially available. Though not fully flexible, they are designed such that every second seeding unit can be closed. Whit such systems, row cropping can be established only in the areas where it makes sense due to reduced soil fertility or structure. For more reasons, there is a big interest in establishing cover crops. This can be quiet challenging under Nordic conditions as the cover crops in general require early seeding for success. Here, row cropping also enables some good conditions under seeding in the inter-row band prior to harvest. In good conditions cover crops can contribute in stabilizing the growing system due to harvest of nitrogen and controlling weed growth. Though the capacity from cover crops to control weeds is not good enough as it can be used to solve problems, stubble cultivation must be brought into play.

#### **3.2. Weed harrowing and hoeing**

To avoid weed problems it is important that all means to control the weed is integrated and optimized together with other elements in the cropping system. The interactions and the connections to the tillage operations and other factors are described in the sections earlier.

The weed harrow is normally designed with a flexible frame mounted with more sections, equipped with a set of long elastic tines that all are in touch with the soil surface. It is commercially available to have systems, where the load on the individual sections is equally distributed by an active control system. The intensity from the tines to the soil surface is controlled by the load on the section and the working angle for the tines. This working angle can also be controlled by a central control system that is normally controlled by the operator. The challenge for the operator is to adjust the settings for the harrow and the operation forward speed such that the damage on the crop is limited and the effect on the weeds is optimized. One important factor here is to make the best use of all factors to optimize the growth difference, such that the crop continuously is bigger and more established than the weed. It is also important that the soil is workable without a slammed and hard surface. In an optimal setup the first treatment is performed approx. 1 week before the seeding process to initiate the germination of the first generation of weed seeds. Hereafter follows a precision seeding as earlier described; this does reset the weeds. Then, just before the crop breaks the soil surface, a weed harrowing operation is again performed. Hereafter a break is needed for the crop to be established such that it sustains a next operation. For this operation the operator needs to pay the most attention to the timing and to the adjustment of the harrow as the best result is achieved by carrying out the operation as early as possible, without damaging the crop and when it is still possible to control the weed. Hereafter two more operations can be performed.

As described the weed harrow is a uniform implement that work in the full working with based on the preconditions that it is possible to establish a difference in the sensitivity for the crop and the weed to the treatment. In comparison to this is the hoe that only operates in the inter-row area without crops. By modern implements the guidance of the hoe can be automatically controlled by a vision-based system that enables the hoe to operate quite precisely in relation to the row. As the competitiveness from the row of crops is bigger and closer to the row, it is important to perform hoeing as close as possible without absolutely damaging the crops. A very precise and dedicated operation can be performed by a hoe equipped with elements such as brushes or other tools that work close to the row. The advantage of the hoe is that it has very high efficiency in the inter-row area.

A normal cropping system does normally include weed harrowing for weed control. The overall effect and weed control can be improved by also introducing the hoe for operations where it can be possible operated. Compared to weed harrowing the hoe is less sensitive on hard surfaces and so on, which means that the effect of hoeing is more reliable. Hoeing can also be an important part of the strategy to bring the system back to normal for areas where the weed has had the chance to develop to a level that is problematic for balance in the system. This can be done by opening the rows to make space for the hoe operations in the problematic areas in the field. The hoe is very efficient in the inter-row area. For the operation close to the row some additional systems can be built [21] such as flexible tines or rotating fingers.

## **4. Discussion and conclusion**

for seeding: one is that the seed is distributed evenly over the area to give the best coverage possible and thereby the best competitive strength against weeds. Danish experiences show good results with this system for crops such as rye and barley. If the crop is less competitive in general, or particularly in the early stage, another system can be favorable, to grow crops in rows this enable the possibility of performing weed harrowing and hoeing. In row cropping, the competitive strength due to weeds in the in-row area has improved substantially, as also the overall resistance for the crop in operations as weed harrowing is improved. The disadvantage of row cropping is that operations for weed control are needed in the inter-row area. Due to yield the crop is not that sensitive. The Danish test has shown that for row distances, up to approx. 18 cm for cereals, there is almost no decrease in yield. Other crops such as rape

Due to seeding there are commercial systems that allow for graduated seed density over the field. The graduation can aim for eliminating locally weak conditions for germination or if an improved coverage is required in the early stage. The control input for this must be given by the operator prior to the operation, as there are no systems available that can sense the input for this. Modern seeding implements are designed to operate with a constant seeding depth, with mechanical means that is adjusted prior to the operation in the field. Ongoing research aims to develop systems that by monitoring the actual working depth are adjusted by a dedicated control system. In the system tested the control systems are operating individually on each seeding section. With such a system in operation I will make sense to expect a coming version designed for adaptive control of the seeding depth, for example, to ensure the access

Systems for automatic change from broad seeding to row cropping are also commercially available. Though not fully flexible, they are designed such that every second seeding unit can be closed. Whit such systems, row cropping can be established only in the areas where it makes sense due to reduced soil fertility or structure. For more reasons, there is a big interest in establishing cover crops. This can be quiet challenging under Nordic conditions as the cover crops in general require early seeding for success. Here, row cropping also enables some good conditions under seeding in the inter-row band prior to harvest. In good conditions cover crops can contribute in stabilizing the growing system due to harvest of nitrogen and controlling weed growth. Though the capacity from cover crops to control weeds is not good enough as it can be used to solve problems, stubble cultivation must be brought into play.

To avoid weed problems it is important that all means to control the weed is integrated and optimized together with other elements in the cropping system. The interactions and the connections to the tillage operations and other factors are described in the sections earlier.

The weed harrow is normally designed with a flexible frame mounted with more sections, equipped with a set of long elastic tines that all are in touch with the soil surface. It is commercially available to have systems, where the load on the individual sections is equally

are even less sensitive to the open row distance.

22 Biological Approaches for Controlling Weeds

to moister and thereby the best possible conditions for germination.

**3.1. Digital tools**

**3.2. Weed harrowing and hoeing**

Many farmers and research activities have shown that it is possible to control the weed in cropping systems only by use of mechanical and agronomic means. It is essential that the cropping system is carefully planned and adaptively optimized in relation to the local conditions and challenges. The fertile soil is key both to the growth and to the yield of the crops but also in relation to create the best conditions for successful tillage operations and weed control. One of the core elements is if the cropping system makes space for cutting grass. A perennial grass for feed that is cut three times or more in the growing season contributes substantially to weed control and to the optimizing the soil fertility and hereby the soil structure.

[8] Jacobs A, Helfrich M, Dyckmans J, Rauber R, Ludwig B. Effects of residue location on soil organic matter turnover: Results from an incubation experiment with 15N-maize.

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25

[9] Perkrun C, Claupein W. The implication of stubble tillage for weed population dynam-

[10] Brandsæter LO, Mangerud K, Helgheim M, Berge TW. Control of perennial weeds in spring cereals through stubble cultivation and mouldboard ploughing during autumn

[11] Shahzad M, Farooq M, Jabran K, Hussain M. Impact of different crop rotations and tillage systems on weed infestation and productivity of bread wheat. Crop Protection. 2016;**89**:

[12] Gruber S, Claupein W. Effect of tillage intensity on weed infestation in organic farming.

[13] Benaragama D, Shirtliffe SJ, Gossen BD, Brandt SA, Lemke R, Johnson EN, Zentner RP, Olfert O, Leeson J, Moulin A, Stevenson C. Long-term weed dynamics and crop yields under diverse crop rotations in organic and conventional cropping systems in the

[14] Nielsen SK, Munkholm LJ, Aarestrup MH, Kristensen MH, Green O. Plough section control for optimised uniformity in primarry tillage. Advances in animal bioscience. Precision

[15] Huang J, Poe R. Weed Spotting By Drone. Vol. 65. Washington: Agricultural Research;

[16] Lambert J P T, Hicks H L, Childs C Z, Frexkleton R P. Evaluating the potential of unmanned aerial systems for mapping weeds at field scales: A case study with *Alopecurus* 

[17] Murphy S D, Clements D R, Belaoussoff S, Kevan P G, Swanton C J. Promotion of weed species diversity and reduction of weed seedbanks with conservation tillage and crop

[18] Legere A, Samson N. Tillage and weed management effects on weeds in barley-red clo-

[19] Lyon DJ, Young FL. Integration of weed management and tillage practices in spring

[20] Cordeau S, Smith R G, Gallandt E R, Brown B, Salon P, DiTommaso A, Ryan M R. Timing

[21] Pannacci E, Lattanzi B, Tei F. Non-chemical weed management strategies in minor crops:

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ics in organic farming. Weed Research. 2006;**46**:414-423

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or spring. Crop Protection. 2017;**98**:16-23

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2017. pp. 1-3

161-169

Going a little into the details and interdependency of the different elements and operations in the cropping systems, it appears that there are many balances to be aware of and many optimizations to be made. Here, many new technologies can assist in positive results. In this matter it is important also to follow technical development. Some of the concepts that automatic solutions. This must create value in the operation and the cropping system, but it also prepares the farmer to take in the new technical solutions when they are ready and when they potentially can create value in the individual cropping system.
