Environmental considerations when growing crops

Environmental considerations when growing crops

26 July 2020

When deciding to grow a spring crop, there are many considerations, from selecting crop type and achieving the best yield, to minimising any potential impacts on the surrounding environment.

While sowing a crop can help fill a feed deficit at a critical time of the year, if managed poorly, it can also increase the risk of losing nutrients from your farm.

Phosphate can be lost to waterways when soil and sediment is washed from a cultivated paddock via surface runoff. Meanwhile, nitrogen (N), in the form of nitrate, can be lost from the reaches of the crop by leaching below the plant’s root zone.

Ensuring good farming practices are implemented will significantly reduce this risk.

For phosphate, paddock selection should be a key consideration. Making sure you identify and manage critical (sediment) source areas, and plan for how these areas will be managed during grazing, can significantly reduce the amount of soil and sediment lost from cultivated/grazed areas. On top of this, leaving buffer zones between cropped areas and waterways to act as a filter strip will help prevent sediment and nutrients from reaching the waterway in the event of heavy rainfall.

Managing N loss (leaching down through the soil profile) can be more difficult. The amount of N loss risk is dependent on several factors, including the total area cropped, the type and rate of fertiliser applied, cultivation method, previous history of the paddock, the time of the year the crop is harvested and how it is harvested (e.g. grazed in the paddock or cut and carried).

Your Fonterra Nitrogen Risk Scorecard is a useful tool to help you understand how these factors influence the N loss risk of your farm. Developed from the information you provide in your annual Farm Dairy Records, the Nitrogen Risk Scorecard assesses six on-farm risk factors. These risk factors are stock management, N fertiliser, supplementary feed, effluent management, cropping and cultivation, and lastly irrigation. These factors each receive an individual risk rating, from very low to very high, based on the estimated impact that these have on the potential loss of N from your farm system.

Within the cropping section of the Scorecard, the main driver of N loss risk is the cultivation method and the total area cultivated. Full cultivation, compared to minimum tillage or direct drilling crops, presents a higher risk, as it can stimulate faster soil organic matter decomposition and mineral N release. When this mineral N release doesn’t coincide with crop uptake, it increases the risk of leaching.

Ensuring the correct timing and amount of fertiliser to match the crop requirements will also minimise the risk of losses. Soil testing is recommended to ensure the selected paddock is at agronomic optimum for your crop. Mineral N tests can help to determine if any subsequent post-emergent N fertiliser dressings may be required and at what rates. Often paddocks coming out of long-term dairy pastures can supply enough mineral N for establishing crops.

Another important factor in managing the risk of nutrient loss from crops is the time of the year the crop is harvested. Harvesting crops in autumn/winter possess a greater risk than harvesting in spring/summer.

Grazing crops during wet winter conditions can increase the risk of pugging. This can lead to the loss of soil structure, meaning water can’t infiltrate the soil as easily, and there’s an increase in surface runoff. Strip grazing a crop can also deposit large amounts of nutrient from dung and urine on a small area. Planning your crop rotation, so that you minimise the amount of time soil remains bare or fallow, by introducing a catch crop can utilise these excess nutrients and grow extra valuable dry matter (DM) in a cost-effective way.

You will receive your Nitrogen Risk Scorecard for the 19/20 season in the first week of October. If you have any questions, feel free to contact your Sustainable Dairy Advisor.