INTENSIVE VEGETABLE PRODUCTION IS COMMONLY ASSOCIATED WITH APPRECIABLE NO3- CONTAMINATION OF WATER BODIES, AS OCCURS WITH THE GREENHOUSE-BASED SYSTEM OF SOUTH-EASTERN SPAIN. ESSENTIAL TO REDUCING NO3- LEACHING LOSS FROM VEGETABLE PRODUCTION IS IMPROVING N USE EFFICIENCY. THE COMBINED FERTIGATION AND DRIP IRRIGATION SYSTEMS USED IN ALMERIA AND ELSEWHERE HAVE THE TECHNICAL CAPACITY FOR SPOON-FEEDING N TO CROPS AS REQUIRED, BECAUSE OF VERY FREQUENT SMALL APPLICATIONS OF N. CURRENTLY, GROWERS MANAGE N BY EXPERIENCE USING STANDARD RECIPES. GROWERS REQUIRE MANAGEMENT TOOLS TO EXPLOIT THIS ADVANCED TECHNICAL CAPACITY. A TECHNIQUE OR COMBINATION OF TECHNIQUES FOR MONITORING CROP N STATUS AND/OR THE IMMEDIATELY AVAILABLE N SUPPLY IS REQUIRED. SUCH TOOLS WILL ENABLE RAPID CORRECTION OF THE N SUPPLY, THEREBY ENSURING CONTINUAL OPTIMAL CROP N STATUS. PLANT/CROP MONITORING APPROACHES ASSESS CROP N STATUS, AND SOIL MONITORING PROCEDURES EVALUATE THE AVAILABLE SOIL N SUPPLY. THIS PROJECT WILL PROVIDE A COMPREHENSIVE EVALUATION OF THE MOST RELEVANT N MONITORING APPROACHES, IN TWO SWEET PEPPER CROPS GROWN IN SOIL IN A GREENHOUSE. IT WILL IDENTIFY WHAT ARE THE MOST SENSITIVE AND PRACTICAL N MONITORING METHODS AND PROVIDE SUFFICIENCY VALUES. EVALUATION WILL BE CONDUCTED BY RELATING MEASUREMENTS TO CROP NITROGEN NUTRITION INDEX (NNI) VALUES AND YIELD, AND OTHER AGRONOMIC PARAMETERS. THREE PROXIMAL OPTICAL SENSOR TECHNOLOGIES, CANOPY REFLECTANCE, CHLOROPHYLL (CHL) FLUORESCENCE, AND LEAF CHL MEASUREMENT WILL BE USED, WITH MEASUREMENTS EVERY TWO WEEKS. CANOPY REFLECTANCE, WHICH IS A WELL-ESTABLISHED MONITORING METHOD WITH CEREAL CROPS WILL BE MEASURED, USING A RANGE OF COMMONLY-USED INDICES, WITH THE CROP CIRCLE ACS470 SENSOR, AND AS NDVI WITH THE MUCH CHEAPER, FARMER-FRIENDLY GREENSEEKER HAND-HELD SENSOR. THE MULTIPLEX FLUORESCENCE SENSOR WILL MEASURE FLAVONOLS, CHL AND THE RATIO OF THE TWO KNOWN AS NITROGEN BALANCE INDEX (NBI). LEAF CHL WILL BE MEASURED WITH THE SPAD 502 AND THE MUCH CHEAPER, FARMER-FRIENDLY ATLEAF+ SENSOR. THE MORE TRADITIONAL AGRONOMIC APPROACHES OF PETIOLE SAP NO3- TESTING AND LEAF TOTAL N ANALYSIS WILL ALSO BE EVALUATED. TWO METHODS OF MONITORING SOIL SOLUTION NITRATE IN THE ROOT ZONE WILL BE STUDIED; BEING CERAMIC CUP SOIL SOLUTION SUCTION SAMPLERS AND THE 1:2 SOIL:WATER EXTRACT METHOD WHICH IS USED WITH SOIL-GROWN VEGETABLE CROPS IN DUTCH GREENHOUSES. IN EACH OF TWO CROPS, THERE WILL BE FIVE N TREATMENTS, TWO DEFICIENT, ONE SUFFICIENT AND TWO EXCESSIVE. NNI VALUES FOR EACH TREATMENT WILL BE OBTAINED AFTER DERIVATION OF THE CRITICAL N CURVE FROM A SERIES OF BIOMASS SAMPLINGS. FOR INTERMEDIATE DATES BETWEEN BIOMASS SAMPLINGS, NNI WILL BE DETERMINED BY INTERPOLATION. ALL PLANT/CROP MONITORING MEASUREMENTS WILL BE RELATED TO NNI VALUES FOR EACH TWO WEEKLY MEASUREMENT. MEASUREMENTS WILL ALSO BE RELATED TO OTHER AGRONOMIC PARAMETERS SUCH AS YIELD. COMMON RELATIONSHIPS WILL THEN BE DETERMINED FOR PHENOLOGICAL PERIODS AND FOR WHEN RELATIONSHIPS ARE STATISTICALLY SIMILAR. SOIL MONITORING METHODS WILL BE ASSESSED SIMILARLY, AND BY EVALUATING ESTABLISHED VALUES. SUFFICIENCY VALUES WILL BE DERIVED USING PROCEDURES PUBLISHED BY OUR GROUP. ALL THE MONITORING METHODS WILL BE COMPARATIVELY EVALUATED IN TERMS OF SENSITIVITY, CONSISTENCY, SUITABILITY FOR FARM USE AND EASE OF USE. AN ADDITIONAL TRIAL WILL EXAMINE THE CONSISTENCY OF MEASUREMENTS AND RELATIONSHIPS WITH CROP N STATUS OF THREE DIFFERENT SWEET PEPPER VARIETIES GROWN AT TWO RATES OF N.