Planty Organic 5 year: evaluation of soil fertility, nitrogen dynamics and production.

Summary

In the Planty Organic experimental field, located at the SPNA location ‘Kollumerwaard’, an organic arable farming system is developed based on three principles:
• Nitrogen input fully based on leguminous crops
• Use of farm-produced cut-and-carry fertilizers
• Reduced tillage; no ploughing.
The results of this research will be available for improvements in both organic and conventional arable farming. The experimental site consists of six plots, 0,8 hectare each. There is a six-year rotation, which means that each crop is present each year in a different plot.. The project started in 2011. Since 2012 year-reports have been published. For this evaluation of the system results the start-up year has been left out and the data of 2012 – 2016 are used for analysis.
It has been shown that it is possible to fulfil the three principles. Nitrogen deliverance to the crops has been realized by means of cut-and-carry fertilizers, green manures and crop residues. Yield level was at an acceptable level and the weed pressure was controllable. Five years without adding minerals did not result in a decrease in mineral content of soil and crops.
The organic matter content of the soil has been measured each year. The measurements’ error is too big to enable reliable statements on changes. Five years of data show a trend towards a small increase of 0.03 % per year. This is remarkable for a system without external organic matter input.
Data from the six plots have been used in the Ndicea nitrogen and organic matter model. The differences between measured and simulated levels of soil mineral N are relatively small. The model seems to give a reliable description of the systems’ nitrogen dynamics.
The simulated organic matter dynamics of the six plots indicate a stable situation. As is the case with the measurements, there is uncertainty in the modelling. Nitrogen leaching as simulated in Ndicea is very limited. This can be explained by the, in average, very low levels of soil mineral nitrogen, and by the relatively high rate of crop cover during the years by cut-and-carry fertilizers grass/clover and alfalfa/clover and by green manures.
The modelling enables a detailed view into the internal nutrient dynamics. This shows that, related to the output in products, a large amount of nitrogen and phosphorus (and other nutrients) is circulating by means of root- and crop residues, green manures and cut-and-carry fertilizers. This high rate of circulation might be an essential factor in system stability and productivity.
Nitrogen mineralisation coming from different sources of organic matter is more and more involved when nitrogen fertilization recommendations are made. In case of phosphorus this has never been explored up to now. The Planty Organic experiment offers an opportunity to study the importance of the internal phosphorus circulation related to phosphorus availability for crop growth.
Due to absence of input (except for nitrogen: leguminous crops) there is a negative mineral balance for all nutrients, which in the end is not sustainable. Mining of phosphorus (and other nutrients) is not sustainable either. As compensation for the loss of nutrients by selling produce, a limited input of compost could be considered, with phosphorus equilibrium as target. On the other hand, for an interesting contrast with other systems and the study of internal phosphorus dynamics, a zero input strategy might be continued for some years.
Besides the produce, the Planty Organic system delivers services without being paid for: very low nitrogen leaching, no ammonium emission, very low methane and nitrous oxide emissions, preservation or increase of soil fertility, no emissions of crop protection residues to water or air, a high above-ground biodiversity, probably a high soil biodiversity, probably limited carbon dioxide storage, no manure transport, no animal welfare violence.