Abstract
Excessive N application occurs in greenhouse vegetable production. Monitoring methods of immediately available soil N are required. [NO3−] in soil solution, sampled with ceramic cup samplers, and [NO3−] in the 1:2 soil to water (v/v) extract were evaluated. Five increasing [N], from very N deficient (N1) to very N excessive (N5) were applied throughout three fertigated pepper crops by combined fertigation/drip irrigation. The crops were grown in soil in a greenhouse. Soil solution [NO3−] was measured every 1–2 weeks, and extract [NO3−] every 4 weeks. Generally, for treatments N1 and N2, both soil solution and extract [NO3−] were continually close to zero, and increased with applied [N] for treatments N3–5. The relationships of both methods to the nitrogen nutrition index (NNI), an indicator of crop N status, were assessed. Segmented linear analysis gave R2 values of 0.68–0.70 for combined data from entire crops, for both methods. NNI was strongly related to increasing [NO3−] up to 3.1 and 0.9 mmol L−1 in soil solution and extracts, respectively. Thereafter, NNI was constant at 1.04–1.05, with increasing [NO3−]. Suggested sufficiency ranges were derived. Soil solution [NO3−] is effective to monitor immediately available soil N for sweet pepper crops in SE Spain. The extract method is promising.
Highlights
170,000 ha of greenhouses and plastic tunnels [1] are used for intensive production of vegetables in the Mediterranean Basin
These greenhouse production systems are commonly associated with N applications that appreciably exceed what is required to ensure high yields [2,3]
After 30 days after transplanting (DAT), when the crops had received the N treatments for approximately 20 days, soil solution [NO3 − ] in the N1 and N2 treatments remained low with values of 0.0–2.2 mmol L−1 until the end of the crops
Summary
170,000 ha of greenhouses and plastic tunnels [1] are used for intensive production of vegetables in the Mediterranean Basin. These greenhouse production systems are commonly associated with N applications that appreciably exceed what is required to ensure high yields [2,3]. Irrigation is often excessive to crop water requirements [3,4,5]. In approximately 90% of these greenhouses, crops are grown in soil [11]. Most of the greenhouse production areas in Almeria have been declared nitrate vulnerable zones (NVZ) [12] in accordance with the EU Nitrates Directive [13]
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