Jørn Nygaard Sørensen

Soil Nitrogen Depletion by Vegetable Crops with Variable Root Growth

The ability of carrot, leek and white cabbage to deplete the soil inorganic nitrogen (N) pool was studied. All three crops are late-harvested crops with a long growing season, but they have been found to have very different root growth. At their optimal N supply, carrot left 27 kg nitrate-N ha-1 in the top 100 cm of the soil, leek left 87 kg N ha-1 and white cabbage left only 11 kg N ha-1, in accordance with previously published differences in rooting depth among the three crops. Compared at a supply of 160 kg N ha-1, 52, 65 and 4 kg nitrate-N ha-1 was left in the soil by carrot, leek and white cabbage respectively. Apart from an extensive root system, white cabbage also had a much higher N-uptake capacity than the two other crops. The significance of differences in root growth, N-uptake capacity and other factors in determining the ability of the three crops to deplete the soil inorganic N pool is discussed.

An Organic and Environmentally Friendly Growing System for Greenhouse Tomatoes

ABSTRACT Greenhouse tomatoes were grown in open beds, confined beds, or in a new system of combined beds. The growing medium and fertilizer consisted of composted deep litter, peat, and hay of a mixture of clover and ryegrass. In the open beds, plants were grown in this compost slightly incorporated into the top soil. In the confined beds, plants were grown in compost placed on wheat straw. The combined beds were identical to the confined beds except for holes in the vertical sidewalls of the container, which enable the roots to grow out into the soil. Plants grown in confined and combined beds produced the earliest yield. Approximately 18% of the fruits produced in the confined beds developed blossom end rot. Plants grown in combined beds produced the highest yield, whereas those grown in confined beds produced the lowest. This yield reduction and the problems with blossom end rot were caused by a high ion activity ratio in the root zone of the confined beds. Besides high yield, this experiment showed that the new system of combined beds reduced the risk of nutrient losses due to leaching especially when supplemental fertilizer was applied.

Undersowing Legume Crops for Green Manuring of Lettuce

ABSTRACT The objective of this experiment was to investigate the potential of several species of undersown legume crops to deplete soil nitrate and to accumulate nitrogen (N). A further objective was to measure the effects of the legume crops as a green manure for a succeeding early lettuce crop. In two years, different undersown legume crops were compared with a control treatment where no crop was undersown. In November, at the end of their growing season, the legume crops reduced the content of mineral nitrogen in the top 1 m of the soil to one third of what was available when no crop was undersown. The N uptake in shoots and roots was in the range of 100–160 kg ha−1. The legume crops were incorporated at the beginning of April the succeeding year. In May, the content of soil mineral nitrogen was 3–4 fold the content in November. The main increase was seen in the top 0.25 m profile of the soils in which the legume crops had been grown. In July, the N mineralized from the incorporated legume crops and from other soil organic matter was estimated to be 36 and 38 kg ha−1, respectively. The yield of lettuce was increased by 20–45% when grown after legume green manure crops compared with the control treatment. The yield level was comparable to that obtained in conventional horticulture.

Nutrient availability, photosynthesis, and growth of parsley fertigated with chicken manure extract and lupin sap

Abstract: A greenhouse experiment with parsley was conducted to investigate the effects of organic liquid fertilizers on biomass yield, photosynthesis, root zone pH, electrical conductivity, and nutrient concentrations of plant tissue and growing medium. Limed peat with 20 kg m-3 composted chicken manure was used as the growing medium. Four organic fertilizer treatments based on chicken manure extract and lupin sap were compared with conventional inorganic liquid fertilizer and no liquid fertilizer (only solid fertilizer). Chicken manure extract resulted in a higher biomass yield than lupin sap (6.7 g dry matter compared with 5.8 g) but lower than inorganic fertigation (8.4 g). Photosynthesis was not influenced by type of fertigation. Growing medium pH was between 7.4 and 8.5 in all organic treatments and one to two units higher than in the inorganic treatment. Electrical conductivity was highest in the lupin sap treatment. The root zone concentrations of NH4, K, Cl, and Na were found to be higher in the organic treatments. Inorganic fertigation, on the other hand, resulted in higher concentrations of NO3, Ca, and Mg. Concentrations of P and most of the micronutrients were at deficit levels in the lupin sap treatment. The addition of extra micronutrients to lupin sap increased the tissue concentrations but not the biomass yield. Among the organic treatments, chicken manure extract showed the most favourable root zone conditions and biomass yield.

Stepwise incorporation of white clover (Trifolium repens L.) as fertiliser increases nitrogen fixation and improves nitrogen retention when intercropped with leek (Allium porrum L.)

Background and aimsWe investigated whether the incorporation of intercropped white clover as a split-dose fertiliser improves N retention of the plant-soil system in leek production.MethodsWhite clover and leek were grown in pots where clover was stepwise incorporated into soil as fertiliser. Half of the clover was incorporated before leek transplantation (LT), the other half was incorporated 26 (S1) or 41 (S2) days after LT, compared with full incorporation of all clover (F) before LT. 15N injection and leaching studies were performed to investigate interspecific competition and the effects of precipitation on soil N availability.ResultsStepwise incorporations increased or had no effect on leek growth, despite competition for N between white clover and leek. Compared to F, leek grown with stepwise incorporations had similar and lower N accumulation before the second incorporation, but N was higher at the end of the experiment. N2 fixation by white clover increased the total N input into soil and matched N availability with leek N demand and growth rate. Loss of inorganic N by leaching was lowest in S2 and highest in F.ConclusionsStepwise incorporations of white clover improved N retention in the plant-soil system and could be used to increase leek yield.