Developing soil-applied adjuvants for agriculture
In agriculture , weeds compete
with target crop species for space , water and nutrients in the soil , which can affect their growth and reduce yields . The most common and effective way to eliminate weeds and optimise yields is via chemical pesticides , especially pre-emergent herbicides . There is increasing pressure to manage these carefully , as many are applied directly to the soil and so can potentially enter waterways . When a spray solution is applied to soil , it follows the path of least resistance , moving around hydrophobic regions and leaving pockets of untreated soil . This may allow weed seed germination and the establishment of other diseases and insect infestations . The inclusion of a soil adjuvant improves the delivery of pre-emergent herbicides by reducing surface run-off , increasing soil penetration , distributing the application more evenly and reducing the number of unprotected spots . Although yields can be optimised through the application of chemical herbicides , it is important to acknowledge the role that soil quality can play in limiting land output and efficiency . Poor soil quality can result from inadequate fertilisation , infrequent crop rotation or overfarming of the land .
Two key issues which fall into this bracket and which can be impacted by adjuvant application are soil compaction and soil nutrition . The former occurs frequently in intensively farmed land , resulting in the compression of pores that would otherwise transport water and air . This impedes root growth in crops and can cause oxygen deficiency . Soil compaction can contribute to a severe decrease in yield . Reducing the number of applications required can also reduce soil compaction . Water shortages and droughts cause essential nutrients , such as nitrogen , phosphorus , boron and potassium , to concentrate into pockets where it is difficult for plant roots to reach them . Flooding and precipitation leaches nutrients out of the soil and often erodes the top layer of the soil itself . Facilitating surface water penetration can maintain and protect soil and nutrient erosion caused by excessive rainfall . It is difficult for spray solutions to penetrate poor quality soils effectively . Therefore , the addition of a soil adjuvant can provide improvement , helping to overcome the problems described previously . Adjuvants can be used to increase the efficacy of soil-applied herbicides , insecticides and liquid fertilisers by facilitating root uptake mechanisms .
It is important to optimise and balance multiple surfactant modes of action to ensure the adjuvant performs properly when applied in the field . An example of this is Hydravance * 200 , which was designed to deliver four key modes of action ( MoAs ). This article describes these MoAs , how they are technically addressed and their impact .
Increased penetration
It is difficult for water to penetrate soil due to a high natural surface tension . Water penetration is essential to achieving crop growth , because plants require water for healthy development and the only water accessible to plant roots is contained in soil below the surface . In addition , agrochemical treatments typically have water-based delivery systems and need to penetrate into the soil . The soil adjuvant reduces the surface tension of spray solutions , which allows it to be readily absorbed into hydrophobic soil , increasing penetration . By modifying the surface tension of the spray solution , the adjuvant reduces surface run-off and pooling . This enhances delivery of the treatment into the soil where it needs to be in order to be effective . Figure 1 depicts a spray droplet with and without the inclusion of the
20 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981